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.