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.

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.

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!

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 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 ...?

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.

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.

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!

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.

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.