31 December 2020

20m magloop update

Considering the success with a magnetic loop for 20 metres, now I wanted to be able to use a bit more power than 2.5W (at 5W it heated the RG-58 coaxial capacitor, at 10W the tip produced sparks).

I got a thicker coaxial cable that serves both as main loop and coaxial capacitor stub. That's about RG-213 size, with 3 mm solid copper inner conductor: the main loop is stronger, but the stub gets more on the way. Also soldering the whole thing together was not easy, let alone cutting the capacitor to the right length!

The current upgrade is shown in the picture at the right. The loop is slightly longer than Spring 2020 edition, while I have not modified the small coupling loop: this results in SWR of 3:1 at resonance point. Still, reports on the reversebeacon.net are a bit better than with the previous version.

First task for 2021 will be to fix the coupling loop to get a match as close a possible to 1:1. And do have some CQ QSOs!

29 December 2020

FNIRSI DC-6006L Power Supply and a bug

During "Black Friday|Week" 2020 I bought the DC power adapter FNIRSI DC-6006L. I would not call it a "power supply" since it requires an AC-DC adapter (like an old laptop PSU). Provided there is enough "juice" provided by the external PSU, the DC-6006L is capable of 0.1-60V output up to 6A: that's 360W in a aluminum case lighter than a smartphone and smaller than a sandwich! You can find a good description of the product (in decent English language) on their website or on the usual Far East sources that sell it.

Check out the size comparison with the Nissei SPS-250A:

FNIRSI DC-6006L vs Nissei SPS-250A.

First things first. The Fnirsi unit is not very RF silent, so it will increase the background noise if used to power an HF receiver. But it works OK as a lab power adapter.

I have found one dangerous bug. When DC is applied to the input of the DC-6006L, there appears voltage on the output even though it is configured to start in OFF position at "cold boot". It might last 100-200 milliseconds, enough to burn whatever is connected on the output! Looking at the output on the oscilloscope, the voltage reaches 6-7V regardless of the output voltage set. I did this test both with 19Vdc input on the barrel jack and with 14Vdc input on banana sockets. I have an analogue oscilloscope so I cannot do proper measurement of amplitude and duration. Just consider that an Arduino based circuit springs to life. This happens before the boot screen appears on the DC-6006L display.

On annoying thing is that the beep cannot be disabled via software. While it is useful when over-voltage/current protection triggers, you might not want to hear it for each key press or knob rotation. And it is quite loud too.

I tried serial communication without the FNIRSI software, but all I get is a string that changes in sync with operator's actions through the front panel controls.

I have drawn 45W on a resistive load without ill effects.

I paid about 30€ and it is worth it, especially if you already have a fixed DC source.

27 December 2020

Eight TIL308 displays in a clock

I would not say that the long lockdown and alike has allowed me to reach the bottom of the to-do bucket, but it slowed down the consumption of projects in the waiting list.

When I spend the whole work-day at the computer, writing firmware in the remaining hours is not so pleasant. In the Xmas break I finished the code for the clock that uses eight Texas Instruments TIL308 vintage LED+logic displays.

Final firmware onboard! I can solder the remaining capacitors to complete symmetry.

Hardware design files and software source code have released to github.

This clock is self-standing if the RTC module is inserted perpendicular to the display board. Adjustments are accomplished through a linear potentiometer and a push-button. With a software trick ;) the same analog input is used both for reading the light-dependent resistor to adjust display luminosity and the push-button. I had to adjust resistor values and add a couple of them outboard.

I like these clocks to do something unexpected, so every 60" it might display a word built using available letters (or lookalike) and numbers:

// Available letters are:   ABCEFIOSG-
// Mapped to these symbols: A8CEF1059B  (mind the mix of letters and numbers!)
// Plus space ("D") and all the numbers are at your disposal!

TIL308 is not a full hexadecimal display because it maps "B" to "dash" and "D" to whitespace. This reduces the possibilities of long words and exercises your fantasy a bit further to find meaningful text to display randomly. Don't forget you can use multiple languages for your words!

A nice addition would be to be able to add words at runtime (and store them in EEPROM), rather than at compile time. That means more firmware to write ...

13 November 2020

New banner picture with 1972 Toshiba logo

After a long time I have changed the banner picture of this blog.

I was looking inside a 1972 CB handheld from Midland and noticed these metal case active elements with a very cute Toshiba signature. Too cute to stay inside the transceiver and not be seen by newer generations. So, here it is, the new banner.

The new banner as of 2020-Nov-13.

And here is a slight zoom-out on the circuit with one of these Toshiba components:

 Really, really nice.


28 October 2020

ICOM BP-84 battery pack

At a slow but steady pace I am working on a 10 GHz WBFM  receive chain not based on RTLSDR. The path requires having a receiver capable of WBFM at 600-700 MHz, which is covered by most "scanners".

Recently I bought an ICOM IC-R1 without battery packs, so I sourced one large enough to contain an energy source both for the receiver and the LNB.

I bet on a BP-84 hoping it would be tall enough to contain 18650 LiXx cell and it does indeed.

LtoR: BP-84 shell, AA for reference, 6x custom NiCd cells, 2x 18650.

Since the project around the IC-R1 scanner has been put aside in favour of another scanner, I will write only about "how to remove the original content of BP-84?"

First of all, the bottom cover must be removed. My BP-84 came with the cover already off: saw it off carefully since you will not split in two parts the shell. Once the bottom of the cells is exposed you need to cut off three metallic tabs (visible in the picture) which also hold in place the 6 NiCd cells. Once the three tabs are loose, the 6-cells pack can be pulled out with slight force.

A 18650 Li-xx battery is perhaps 1 mm taller than those custom size NiCd's. But given that the BP-84 bottom is now lost, you can handle the extra length when building a new bottom.

Three 18650 in [v^v] shape (zig-zag) should fit in there. That gives 12.6V to 10.5V. Consider adding a fuse and a Li-xx protection circuit. The 12V line can go out to a power injector towards the LNB so everything is self-powered. Enjoy!

13 October 2020

Kit Oscilloscope Clock 8SJ31J review - 3

Since I have written a review of this kit I have been asked to share pictures of my build. I am unsure how useful they can be, maybe just reassuring.

IMPORTANT. DO NOT RELY on these pictures to decide which component goes where. In order to build that kit you need to be able to use an ohmmeter to sort resistors, read IC markings and understand capacitor values. Also, the kit seller (that is NOT me) may change components depending on his sources, and some values too.

Click on pictures to get the larger version.

Direct all your questions and problem to the seller, not me.

All pictures are watermarked and cannot be used elsewhere.

How I stacked the two boards, size is about 20x8x7 cm.





11 October 2020

Kit Oscilloscope Clock 8SJ31J review - 2

After few days fiddling with the kit I came up with one further tip for future builders: use a "sort-of" socket for the two fuses F1 and F2. They are not resettable, so if they blow up you need to go back to the soldering station.

Obviously it happened to F2 (filament) in my built kit. Now I fit two machined pins and the new fuse will go there. Moreover I noticed that F2, whose value should be 1A, was marked 750 mA, barely the limit for 2BP1 CRT that requires 600 mA according to the datasheet (but probably more at power up on cold filament).

10 October 2020

Kit Oscilloscope Clock 8SJ31J review - 1

Since I got few small CRT tubes without driving circuitry, I took some time to think of a good way to test them and build a display of some information. I studied circuits found online, considered building just an HV power supply and reviewed DIY kits.

The kit way sounded good, but pricey. Nevertheless, since most firmware has been written and shared, I would have spent lot of time in reinventing the wheel without breathing life to the CRT. The kit choice leaves me time to plan a nice enclosure, instead.

In the end I picked a kit from China, available on aliexpress and other sources for about 60€ delivered. It had good reviews and the design is open (I have not checked if it is derived/copied from others). The original item name is "Kit Oscilloscope Clock 8SJ31J Driver Board Oscilloscope Clock Control Board Kit Creative". The documentation says it works with a dozen CRT models, but voltages are compatible with even more tubes, like those that I have.

The kit has two boards and comes in a packaging that is safer than most other shippings from China. Instructions must be requested by mail to the seller, but what you get is schematic diagrams, one BOM per board, troubleshooting+setup tips and CRT wiring for supported models.

At this point the feeling is like building a kit you have prepared yourself with few added complications: you don't know parts placement, you need to sort-out components (easy, use a DVM!), you have no mid-build smoke tests, some values will be different or parts missing.

Regarding different values (for resistors) you can understand the reason if you can read the schematic. For empty slots on the boards you can make sense of them by looking and studying the schematic diagrams as well. In 3 missing resistor slots I fit 5 Mohm ones to give a better look. I couldn't help, my eye kept falling in that area! (Those 3 resistors are pull-up for data lines which are - in my kit - already soldered in the rotary encoder board.)

Sometimes I found hard to associate the component place with its name because the board is quite dense. In some cases the part name (R54, C11... for example) could have been moved inside the symbol and provided a paper copy of the placement for future reference. Also some pads go directly to the large ground plane and with a small pad area they are hard to solder.

Very first power-up test.

If you will build this kit use your smallest iron tip and your largest patience: there are over 400 pads on the XYZ board and over 300 in the control board!

09 September 2020

Western Electric 6167 Dekatron

I am always alert on vintage display technologies and the latest common thread has started in mid-July 2020 at the first ham/electronics flea market after COVID-19 lockdown.

In Tortona open-air fair I found a Philips DG7-32 cathodic ray tube probably NOS and an 0D3 gas-filled cold-cathode tube. Having a CRT calls for a CRT clock, so I looked around for circuits and other CRTs for you-never-know-what-when. A small stock of National 2BP1 was on sale almost locally and the same guy had recovered a shoebox of NIB vacuum tubes (more on another post).

I poked around the unknown-to-me part numbers and gave them a meaning with the help of the smartphone. Amongst others, I took home a mysterious Western Electric 6167 Dekatron new in box, packed way back in 1958. The picture shows the original packaging, with a now sticky wax(?)+net foil and lots of soft paper. 

A dekatron is a counting device, or divider if you prefer. It is gas filled like a Nixie and some of them display a dot on the current count position. A datasheet is available, but no reference to original applications and circuits. Fortunately someone has already built a spinner with W.E 6167 so it was a matter of replicating the circuit.

Since everyone's junk box and equipment is different, I kept voltages from threeneurons's spinner circuit as a reference and generated them with two power supplies in series: 280V + 170V (make sure the second PSU is floating with respect to earth!). In order to get about 225V I used a sequence of zener diodes, which also provides a comfortable tap at about 60V. Finally, lacking a socket I used pins freed from a DB25 female to interface with the dekatron without stressing the pin-glass seal.

So, thanks to Mike "threeneurons" open work, this baby started spinning right away:

I like its un-usefulness  :)

29 August 2020

Neon Tester TS-990

My neon/nixie/gas-filled-tube tester homemade 5 years ago still works, but it is cumbersome to carry the device and a 12V battery when you need in on the field (A.K.A. flea markets...).

Instead of looking for a different case and fit a LiPo+booster, I decided to buy the TS-990 Neon Tester, that has a comfortable case and works off 4xAA batteries. Hard to beat at 10€/12US$!

Size is about the same :)

I did not expect it to pulse on/off the HVAC every second, but that helps to see the gas in daylight. Also it is more powerful than the CCFL inverter, as it lights up the gas even without touching the tube glass.

28 August 2020

Jam Replay Bluetooth speaker battery replacement

While I've been blog-silent this August 2020, I do have thought of electronics and done some repairs here and there. Like a relative's 10 years old laptop that does not support the latest Win10 updates and needed a clean-up of the CPU fan, or a desk lamp that melted the lamp holder. Usual business I'd say.

Back home, we wanted to use my daughter's Jam Replay Bluetooth Speaker HX-P250 that would not power up. Recharging didn't help since the red LED would not light up. Highly suspect: the battery.

Old (blue) and new (silver) battery.
This speaker is surrounded by an integral rubber cover that can be removed with little patience. Then, four screws on the bottom, two on the side, carefully take apart the three parts (they are connected with THIN wires that can be easily damaged, so be extremely gentle!).

The battery measured 0.587V even after trying a recharge. Way too low. As someone already documented for a similar Jam Replay speaker, cut the old battery away keeping its wires and fit a replacement.

I had a spare 3.7V 400mAh, which has less capacity than the original (meaning shorter play time), but allowed me to close the case in less than 30 minutes and reclaim the lab desk for other projects. You may buy similar batteries online, just pay attention to the dimension, the voltage 3.7V and the technology Lithium-based.

Recharging test.
Before fitting the rubber back in place I tried a recharge and a pairing session. Both were positive, so now the speaker awaits the next opportunity to be heard.

Personal note. Keep the thing's battery charged up. The circuit might be drawing some little current and without overdischarge protection the battery will be discharged below the point (voltage) of no-return (about 2V for Lithium-x batteries). We hadn't used the speaker for months.

25 July 2020

Independent glow from a Thyratron tube

Thyratron Glow!
This is a self follow-up of a 2017 experiment with a low-pressure gas-filled vacuum tube, a Raytheon Thyratron 2051. [Well, technically speaking this is not anymore a vacuum tube!]

While we know that the gas inside can be excited with an HVAC source through the glass, that seemed impractical when I wanted to show the lighted tube as if it was a (purple) bulb. So I set up a little test.

I fed the HVAC to the cathode. Touching the glass with my hand lights up the gas. Cool. No shock whatsoever.

Then I tried to close the HVAC circuit to the "cold" pole of the generator through a 10 Mohm resistor: now the gas lights up on its own. That's what I was looking for!

Replaced the resistor with 1 Mohm and there is a slight increase in brightness and, if the glass is touched, the glow spreads and increases.

Last improvement: heat up the filament/heater (I used 5.5 Vdc). This brings the glow to another level which is well noticeable in mid-darkness. The tube warms up too, good for the dark, cold Winter season.

I have seen glow forming at the top of the tube just once, probably while the filament was cooling down. I will experiment more to get a repeatable glow on the top too.

Apologies for the lousy picture. Too much light and you don't see the glow. Wrong white balance and the glow turns into blue (NO!). You need to get one of these if you want to see it, or wait that I set up a better photographic studio (evil grin ... this could lead to a challenge to a colleague who is into photography...)

23 July 2020

Lagomarsino Totalia LD-122

Totalia LD-122 calculator.
According to the date I typed on the keypad, I have owned this Lagomarsino Totalia LD-122 calculator for one year and half. 

I got this calculator in good conditions, just needing external cleaning. It has a Panaplex display, which makes it interesting for me because it glows Neon orange.

The power cord has only live and neutral but at least it is still commercially available (the one that looks like the "infinite" math symbol) so the calculator can be powered up with all the proper care.

Side view with power switch.

The label says "Made in Italy". Really?

LD-122 back view with AC socket.

If I had room on the desk I could use the dust cover between each use.
Dust cover in place!

I should take pictures of the inside to document the technology and study if it can be somehow interfaced with a microcontroller to build the Nth clock...

11 July 2020

My current LoRA "DX" is 64 km

After few experiments with spread factor and the GP antenna, thanks to TTN Mapper service I can visualize which gateways have received my LoRA signal on 868 MHz.

On the South facing balcony the signal travels 64 km at SF7 BW125 and the RSSI is still respectable. The strongest link at SNR = 8 dB is "just" 48 km long. Both of these long distance paths are in line of sight or very close to it. A total of 5 gateways received my transmissions.

When I moved the transmitter on the North facing balcony I hit 3 new gateways, two of which are available on TTN Mapper. The maximum distance here is about 38 km, but there is absolutely no line of sight path between us.

That makes a total of 7 (8) TTN LoRAWAN gateways that can receive and relay to the cloud my LoRA messages

10 July 2020

How to calculate LoRa GP antenna

Say you want to try a GP antenna on your LoRa module. How long should it be? A Ground-Plane antenna consist of 1 radiator and a number of elements mimicking an elevated ground plane. All of these pieces of electrically conductive material (preferably copper wire) should be long one-quarter of wavelength.
Since the wavelength depends on frequency, you need to apply the formula:

element length [m] = 300 / 4 / frequency [MHz]

This means that each element will be:

 Lora Frequency Band [MHz]
GP element lenght [cm]
 868 8.6
 915 8,0

Don't be too picky about millimetric precision of your cuts.

How many elements should you use for the ground plane? In my experiments I used two, 180 degrees apart, because that's the amount of wire I had within hand's reach. If you can use 4, each spaced 90 degrees. With reference to the horizontal plane, ground plane elements should be bent 45 degrees downwards. Again, don't be picky with the angle, but try to be consistent with all elements.

09 July 2020

LoRA GP antenna

Now that I can map my LoRA signal, I can play with RF and try to get the most out of it. The most straightforward way is to use a better antenna, and probably the only chance to increase range/coverage.

SX1276 with a directly
attached GP antenna.

To keep things simple and straightforward I replaced the helically wound antenna with a ground-plane directly at the SX1276 board. While this is not a real-life situation, it works well for side-by-side comparison. Also I should have tuned the GP to resonance, which requires a connector and/or some coax.

The signal strength as measured by far away TTN gateways is some 7 dB better. If I understand correctly LoRA terms, 7 dB means you can reduce the spread factor by two and achieve the same signal quality. Or quadruple the bandwidth.  And you LoRA experts know the role of SF and BW on airtime vs bps vs whatever_LoRA.

The expert eye should note that the helical antenna was used without an explicit ground plane, so this experiment is probably not meaningful at all. I need to go back to the bench and re-install the coil with the same ground plane.


07 July 2020

Simulating a LoRA node GPS position on TTN

A simple way to see your LoRAWAN node or gateway coverage is to use the TTN Mapper service.

In order to get my node visible on TTN Mapper I had to enable the Mapper Integration within my Application and output notes's position. TTN Mapper documentation says that either the node sends its position in the payload or you can "pair" it with a smartphone app and keep both close to each other (ie the same vehicle, the same bag, ...).

OTOH if the node sends its position it must be decoded into a JSON through some code written in the web console, Decoder section under Payload Formats. So, why not write a static Decoder function that returns the required variables?

You need to produce latitude and longitude. Optionally altitude and hdop. If a node isn't moving, that's quite easy! Recover the coordinates in your preferred way (smartphone GPS app, GPS tracker, a web mapping service, ...) and fill in your code like this:

function Decoder(bytes, port) {

  var decoded = {};

  // your node's actual coordinates
  decoded.latitude = X;  // a value like 10.456 (this is North-South or equator)
  decoded.longitude = Y; // a value like 80.123 (this is East-West of Greenwich)
  // your node's height above ground (or is it m.a.s.l.?)
  decoded.altitude = Z;
  // your position accuracy, 5 is fine
  decoded.hdop = 5;

  return decoded;

Once the Decoder function is saved, all further transmissions within your TTN Application will carry those variables (added cloud-side once the data is received through a gateway).

Can you see a cheating danger in here? I do. But fortunately there isn't a LoRA distance competition, yet.

Let's get my signal as far away as possible, as strong as possible!

03 July 2020

RaspberryPI and LoRAWAN with SX1276

I had laying around a SX1276 LoRA module for some months and following an IoT discussion at work I thought it would be the right time to play with it.

Instead of wiring an Arduino board with level converters (or use a 3v3 Arduino Nano, which I have), I opted to use an old, single-core, 512 MB RAM, Raspberry Pi B+: wiring is straightforward and I can debug+control it remotely over SSH.

Not that I have meaningful data to transmit. I am interested in the RF part of the whole thing since 868 MHz lies between 70 and 23 cm HAM bands and everyone writes wonders about the LoRA modulation scheme. Because of that I chose the software that offered the fastest way to get a signal on the air with the support of TTN. I used arduino-lmic-rpi with bcm2835-1.64 driver. The RPi distro is based on Debian 8 with kernel 4.9.35, don't ask me its name.

The TTN part is well documented: you need to create an Application and register your device on their portal. Then get Device EUI, Application EUI and App Key which have to be inserted into the .cpp file. Pay attention that DEUI and AEUI need to be reversed, so LSB first. Compile and run.

If everything is correct and your LoRA node can reach a gateway nearby, your transmissions will begin to appear on the web console. You need a TTN gateway in your area and it must be able to receive your transmission!!

Performance? My signal is being received by 4 gateways and a couple of them seem to be quite far away (but in line of sight).

Nothing new so far, I have only replicated someone else's work.

30 June 2020

Update on iWatRoad scooter

Once I replaced the melted XT60 battery connector in the R9 iWatRoad scooter, the user interface powered up. While the battery measured full 42V, the display said it was empty. So I wired it up to a lab PSU that could provide no more than 400 mA at 42V. It did take current for some 10 minutes and then stopped, still showing empty battery. When we plugged the original charger the LED stayed green, meaning "it's charged".
I think the culprit now lies inside the heatsink box that holds the control board. It is glued to the chassis and it will be removed sooner or later, to have a look inside or to look for a replacement.
Wired-up for charging.

18 June 2020

Dentaku, a Japanese calculator museum (online)

I was looking for info on a quite old Toshiba calculator and Serge Devidts's CalcMuseum had no information about it. Instead I found some data and much more at Dentaku Museum.

The website is in Japanese and you will need the help of Google Translate to go past pictures, dates and prices in the text. There is a whole new world behind the language barrier.

I do not own enough calculators to open a whatsoever museum (23 items at the moment). I had planned to show them at work on my desk, but with the 2020 pandemic that idea has been put on hold.

10 June 2020

Melted XT60 in iWatRoad electric scooter

An dead-in-action electric scooter has been brought to my attention. It is an iWatRoad R9 eXtreme. After reaching a full stop, it shut down and did not move, nor power up again. Nice problem indeed!

Initially I suspected a failure in the one-and-only user interface control: a cheap push button. Too easy, wasn't that.

So I moved to the battery compartment under the footboard. Down there, waiting for me was the battery connector. An XT60 couple mated forever through overcurrent meltdown. Look at the picture! The red pole was moving towards the black one, leading to a big short and probably a fire.

Melted XT60 connector
Melted XT60!

The XT60 couple is not interrupted, but possibly the red wire was disconnected since I pulled it away with no force.

There is one interesting finding. The outer label says the battery is 42V 10.4Ah while the battery itself states 36V 7.8Ah. This means that one charge will last less km. Moreover, if both the scooter producer and the battery producer lied about the capacity, the real capacity might be even lower than 7.8Ah. Note that this iWatRoad R9 was bought in May 2019. Currently, June 2020, their website states the battery is 7.0Ah with 25 km.

External and battery labels don't match.
External label and battery label don't match.

Wait, now that I look closely at the outer label I see that the whole product is something else! It says "E Kick Scooter Model:9X" produced in 2018, distributor Floatup S.L. .What the ...?

04 June 2020

When you think you've got enough parts to complete a project

... and realize you ran out of IC sockets!

That is what happened when I started building the first display board (...clock...) with eight TIL308 displays. I had many sockets around but not enough with 16 pins. I know I can use pin headers but I would like to keep a consistent look. I had to desolder sockets from old boards I built 20+ years ago.

Nevermind, the display board is now alive. I ordered 5 of them from JLCPCB. I have used all I/O pins of Arduino Nano. While I wanted to be able to control the brightness of each digit, I had to resort to group them in couples. I will complete one board and see how it looks if some displays are left out: the two outermost, #3 and #6.

Because the lack of inputs I grouped together (in series) the incoming light detection (day/cloudy/night) with the user interface pushbutton and solve the puzzle in software. Another ADC-only input is for the linear potentiometer which will be used as in the 4x TIL311 clock board.

Hardware plans and firmware will be published on githib.

03 June 2020

NanoVNA as Frequency Counter

Disclaimer. This post describes a proof-of-concept experiment. It can damage your instrument(s). DO NOT replicate unless you fully understand all possible risks, both stated in this document and those not described. If in doubt, do not do it. I cannot be held responsible for any damage caused by attempting the theoretical procedure described below. That said, enjoy reading.

This post answers: "Can a NanoVNA (or a generic VNA) be used as a frequency counter?" Yes, with many quirks and don'ts! So, how?

Using both ports of the (Nano)VNA, we can see the transfer function of a device over a given range of frequencies. A signal is generated at Port 1, which we inject into the device under test, and we read the DUT output on Port 2. If DUT is a band-pass filter we should get the "hill" shape once we configure the VNA to display a trace in format "LINEAR".

In this configuration the VNA measures power at Port2 and shows the difference of Port2-Port1 versus frequency. So, if Port1 is terminated on the 50 ohm dummy load and we let Port2 pick whatever signal is coming from the air, the VNA almost becomes a spectrum analyzer. A pretty deaf one, but it sweeps over the set frequency range.

So, let's say you know more or less where your signal generator is (between 50 kHz and 300 MHz). You configure the VNA to display just one "LINEAR" trace and set the frequency range around the expected frequency. The displayed line should lay on the bottom of the screen because nothing is passing from Port1 to Port2. Now feed the unknown signal to Port2 (more later on how to do it): a peak will build on the line, and that's the frequency you are looking for. I suggest to zoom-in to get a more accurate measurement.

How to feed the signal to Port2? It depends on how powerful it is. My 5W HT could be picked without anything connected to Port2 at 1 metre distance. A weaker signal could be heard with a small wire acting like an antenna. A very weak signal could be fed through a pick-up loop. You would need to experiment and be careful not to fry your VNA input!

Or, better, get a frequency counter.

16 May 2020

Honey, I shrunk the loop

Like most amateur radio antennas, magnetic loop do not receive positive looks from relatives, neighbors and by-passers. My 20m magloop on the balcony could be seen by us and very few other people, but would still hurt the eye when looking out in that direction.

So, I shrunk the loop, from 2.3 m circumference to 1 m. Of course it now operates on a different frequency: 50 MHz. It has been chosen on purpose, since May and June are the Sporadic-E ("ES") season. Thanks to the lockdown and work-from-home situation I stand more chances to be in the shack when ES hits, unpredictable as usual.

I changed the tuning capacitor from an air variable to a RG-58 coax stub, meant to withstand higher voltage, thus input power. It did work on the 20 m loop, but it doesn't on 6 m.

This is what happens. On the VNA the antenna is perfectly matched. On the transceiver the SWR meter is happy.  Then, if you keep the key down, SWR increases to well over 10:1. On the 20m loop the stub tip would produce a bright white spark when I raised the RF power above 30-40W, which was solved by making a bit more space between the braid and the inner conductor. On 6m there was no spark: the RG58 stub would heat up and change the impedance.

IMPORTANT. How to check if it heats? Either use a thermal camera or touch the stub once that both these conditions are met: you have produced the SWR increase AND you have have switched off the transceiver completely (so that it doesn't transmit while you sense the temperature with your fingers).

This is a sign that the voltage at the open loop side is high, so the match is good. Also, being the circumference close to lambda/4, the efficiency is higher and the same holds true for the voltage.

The maximum power the loop can withstand depends on the environment temperature, but the heat produced with 5-10W is negligible and has no effect. At least at 20 °C!

14 May 2020

NanoVNA as Signal Generator

If you are in a hurry and need a quick & square wave signal between 50 kHz and 300 MHz the NanoVNA can come to the rescue. Just set the centre frequency of the stimulus at the value you need and a span of 0 Hz. The signal is then available at port 1.

Be very careful not to overload the output or feed a voltage/signal to it, else the NanoVNA would be damaged! If the procedure and implications are unclear to you, do not try it.

Why does it not work all the way to 900 or 1500 MHz? Because the NanoVNA(-H) uses some clever tricks using harmonics at frequencies above 300 MHz, but you always get the basic signal 0-300 MHz at port 1.

28 April 2020

Longer delay modification for TDL-2023 PIR sensor

I have a TDL-2023 pass-through motion activated sensor that turns on a device. While I have already set the delay to the maximum value with the internal trimmer, the advertised 360 seconds were not enough.

Click to zoom.
On the small board there is a BIS50001 IC, whose datasheet can be found online. The delay is set with an RC combination and can be seen on some schematic diagrams that use the same BIS50001 chip. Starting from the trimmer pins I poked around and found a series of 1 Mohm (trimmer) and 56 kohm (fixed resistor marked R0). Since I need a longer delay I decided to replace the fixed resistor with a larger value, 1 Mohm being probably enough.

Click to zoom.
The smallest resistor I could find is 1/4W but it fits into the case if installed as seen on my picture. The delay is now over 8 minutes. Since I have not been able to locate the capacitor of the delay circuit I cannot confirm the datasheet formula, but the ON time "feels" like twice as much as before.

25 April 2020

An update to my KiCAD library for obsolete LED

I got a new batch of old LED displays and before doing something with them I needed a KiCAD symbol and footprint.

So I added TIL308 and TIL309 to my KiCAD libraries. Also fixed TIL306 and TIL307 that were missing their respective symbols.

My KiCAD library of obsolete displays (Nixie, VFD, LED) is published on a github repository.

Meanwhile I confirm that TIL311 symbol and footprints are correct since I got PCBs, built them and I am enjoying the result.

24 April 2020

Blue dot and leg glow in Z520M Nixie

I love Nixie tubes, and I especially love round top-view ones. Perhaps that is because the first ones I bought were of this kind.

Lately I got one Z520M with the red coating quite damaged (pictures seem to make it look even worse!). Since the red coating can be restored/replicated, I proceeded to test the tube. I was not surprised to find out that it needs to be driven a bit harder than newer Nixies, both because this one is quite old and probably it has been used a lot.

Digits 0 to 2 were behaving normally. When pulling low other digit cathodes only the leg was glowing. If left ON for few minutes the glow transferred to the digit from the area close to the pin. Unfortunately if the digit is switched off for a while the malfunction comes up again the next time the same digit is lit.

Now that I own a variable HV power supply I could experiment with the current through the tube, and saw that the "leg" does not glow if the current flow is lowered closer to the datasheet value. Even 0.1 mA makes a difference. But then the digit is faint or not completely lit (like "5" and "7").

Since the red coating is cracked I could see through the plain glass and note that the leg glow releases the infamous blue dot. It is caused by mercury and overcurrent. Since it does not happen on digits 0-1-2 it could be just a deposit on unused digits/wires and might be cured throughout hours of operation of the same symbol. Perhaps. I will not go further and keep the tube as-is in the collection. (Or make a test harness where I can leave it running for days out of the way in the lab?)

Can you see the infamous blue light through the crack in the coating?

16 April 2020

TTL integrated circuits "collection"

Not a real lockdown project, I tried to organize my "collection" of TTL integrated circuits. These have been piled up in numerical order to ease a future search for a specific part. The picture shows all of them and it is posted here for my own future reference.

I thought I had more laying around, actually. The 74(1)41 Nixie driver are not amongst them because they are the only 74-series ICs that I still use.

At least now I have a group picture in case I (or someone else) need one of these, or I really run out of interesting projects and start designing something out of them.

15 April 2020

Another HV DC power supply

DISCLAIMER. This "project" handles lethal voltages and currents. Do NOT replicate. I take no responsibility for any damage that might occur from replicating or imitating what is illustrated below.

Having lots of time to spend at home to do "whateveryouwant", I started to clean the lab: move stuff around, make room on the desk, prepare a trip to the recycling facility, see stuff under a different light.

I happen to have two 12V power supplies from 1980's, when heavy transformers were dominating the scene and guaranteed RF silence. The first purchase was 12V/2A, then upgraded to 12V/5A (not that I cared about RF noise back then in my CB years!).

Both power supplies, as of April 2020.
They took space in the lab, one partially broke, one was recently upgraded with a step-down converter in place of 7812 so, as the headline suggests, I made a high-voltage DC power supply out of them.

What was (left) inside. Dust included.

D-C rectifier and back2back trafo.
How? I wired the two transformers back-to-back and rectified the AC output. Bonus, since transformers were both centre-tapped, I can select two outputs just by switching the intermediate connection: 170V or 340V. And both transformers fit into one original case!

According to transformer ratings I should be able to draw about 100-120 mA at 170V and half of that at 340V. Then the voltage drops, transformers vibrate and overheat.

The transformer receiving the mains is the bulkier one, from the former 12V/5A PSU, so there is some room for a low voltage output with decent current.

Final look, with HV output yellow/black.
Needed improvements:
  • fuse the AC input
  • fuse the HV output
  • add a damping resistor on the HV output
  • attach the HV output selection switch to the case 
  • add a status LED/lamp
  • add the low voltage output circuit
Unloaded 340V.
Unloaded 170V.

13 April 2020

Cleverly hidden reset button

Like many people involved in COVID-19 lockdown, I am using the opportunity to tidy up home and reorganize things. Something that popped up was a couple of tiny mp3 players/radio/voice recorders, size roughly 4x5 cm.

One of them was "fat", an obvious sign to the trained eye that the Lithium-based battery inside has gone bad. So .... an excellent candidate for looking inside! The second specimen does not hold the charge, so I think it is going down the same road of its brother.

I didn't expect fancy technology, and I was surprised I could read markings on ICs: (RDA)5807M I2C FM radio and AK2117C "Artek Digital Multimedia Chip" (an 8051-like MCU with multimedia I/O).

While looking around the board I noticed a strange "white" component behind the 3.5 mm audio socket. Looking closer I saw that it is a pushbutton! That's why in the picture there is a small screwdriver stuffed into the audio socket.

I tried to push it on the still-intact yellow player and it seems to act as cold reset button. Probably it works for something else too, like triggering firmware update, but I don't really care.

Still, that button has been hidden in a very smart way!

By the way, the RDA5807M chip tunes from 50 to 150 MHz WBFM!

01 April 2020

High voltage DC power supply

Most hobbyist electronic labs are equipped with a variable voltage power supply of some kind. It could be a benchtop commercial box, a modified AT PC PSU, a variable step-down circuit on the output of a 20-30V upcycled (laptop) power supply.

At some point I realised I was missing an important power source for my never ending learning experiments: a variable high-voltage DC power supply. I mean something that would output as much as 300Vdc regulated (I've build it with a switcher, with back-to-back transformers and voltage multiplier) and high current, possibly limited (neither easy nor cheap).

Not long ago in the neonixie mailing list someone mentioned buying a second-hand electrophoresis power supply. A quick check on eBay showed it would cost me 60-100€ for a device capable of 300V and few hundred mA. Unfortunately all of them are in USA or in UK, with large shipping cost. I think there is very little Italian second-hand market for these devices because professional labs need lots of certifications etc etc and probably rent/lease them.

So I patiently waited for something in Italy to be sold online and before the COVID-19 lockdown I bought a second-hand Bio Rad Power-Pac 300: a whopping maximum of 300Vdc at 400mA, digitally controlled.

The power supply at 300 V output between older devices. The Philips DM needs calibration...

The voltage regulation goes from 10 to 300V, while the current can be limited between 5 and 400 mA. Or vice-versa. The only drawback is a minimum load of 4 mA regardless the output voltage, that I can overcome inserting a fixed resistor in one of the 4 parallel outputs.

With 400 mA available I can power a lot of Nixie tubes and valve-based equipment. Or experiment the beauties of electrophoresis!

27 March 2020

Texas Instruments TI-1500

What I found!!
Texas Instruments TI-1500, that's the third calculator I bought at "Barattolo" flea market in Torino. This one was also battery-heavy, with LED display. There were several versions of TI-1500 back in its days, but I think they all share an enclosed rechargeable battery pack. Mine had two Ni-Cd AA that had gone bad. Quite bad, actually.

The leak has spread almost everywhere on the board leaving intact the display (looks good at visual inspection) and probably the keypad (cannot inspected, but the back is clean).

Without batteries.
After removing the batteries I have cleaned the board with white vinaiger and then water. Since the keypad is blocked to the top shell of the calculator, I had to wash it trying to keep water away from it. Also on one side of the top shell the leak had sneaked under the silver coating and water+vinaiger effect broke it from the inside. This is becoming challenging.

I left it dry on the radiator and tried a power up with an external 2.4V power source. Well, the display showed something but no reaction to keypresses.

I've got too many open projects to take properly care of this calculator. It could stay as is, or it could become a sort of numeric display/clock, as usual.

25 March 2020

Canon Palmtronic 8M

Palmtronic LD-8M 3
After the Litronix 2235, I found a "Canon PALMTRONIC LD-8M 3". That is what tells the battery cover in the back. This calculator was being sold without batteries and with the faux-leather soft case.

After the routine cleaning and some action on the power button, it comfortably showed "0" in the rightmost position.

This is a basic calculator with square root, percent and memory.

Buttons feel OK and don't bounce causing typing errors.

Calculator and soft case.
Battery cover with "LD-8M 3".

Now I own two working Canon Palmtronics, the first being a LD-84. Both came without battery damage. A curious coincidence.

Negative number.

24 March 2020

Let it loop

Being in COVID-19 lockdown gives me the opportunity to be on the air during the day, once work time is over. I tried a magmount 20m Diamond mobile antenna on the East-facing balcony, but I managed one contact with my sloppy CW. Well, RBN receivers had me around Europe. But no contacts were possible in PSK31, neither a report on pskreporter service!

So I moved to something different: a magnetic loop. It had to be build with readily available materials: a hula-loop diameter 70 cm (then not needed to keep it in shape), 4 mm solid coax cable (it's too thin for a permanent loop!), a dual-gang air variable capacitor (two sections in series giving 10-130 pF) and FT817 to tune the antenna sur place.

The feeding loop is just a piece of coax "1/5th of the main loop" long. From the coaxial line, the center goes to braid of the small loop on one side, and the coax braid to the braid on the other side. In other words the feedline is terminated with a 44 cm long loop made of thick wire.

It took me a couple of hours to build. Most of the time was spent looking and implementing a solid mechanical solution for the variable capacitor.

The picture shows the resulting loop. It tunes 30 to 10m. On 20m it is about 20 kHz wide for 2 SWR bars on the FT817.