An experience with XIAOMI Mi robot (Roborock) vacuum cleaner (model n. SDJQR02RR).

DISCLAIMER:

The information provided here is intended only to share a specific my own experience. Due to the serious risks to people and property involved in this type of activity, this information is in no way to be considered as a suggestion and/or an invitation to do the same.
This information can be incorrect, misleading and even dangerous.
Everything described here can lead to unexpected results.
I explicitly discourage anybody from repeating similar experiments.

Symptoms:

My cleaner stops working mid cleaning cycle. It goes in a OFF state. The only way to resuscitate it is connecting it to the charging station.
Once it comes back to life I can start a new cleaning cycle, but the cleaner stops again after few tens seconds.

Investigation:

I have managed to replace the 185 resettable fuse on the cleaner's mother board as per “Internet” suggestions: no change.

In order to further diagnose the problem I removed the battery pack from the unit and, after having carefully read the Safety Data Sheet for the product BRR-2P4S-5200S, I’ve removed the bottom (or top, depending from where you look at it) cover getting access to the internal BMS circuit board (the cover is glued, but with a little patience I managed to remove it with very little damage to the plastics).

Characterizing an Advantest R3361B Spectrum Analyzer RF Input with a miniVNA in the 1-180MHz range

As per my knowledge of VNAs this should have been a very easy REFLECTION measurement.

According to the results I get, ...it is not.

I know: the setup itself is questionable due to the differences between Golia (the R3361B) and David (the miniVNA). But this is what I have in hands and this is an experiment done for the purpose of learning something, not to perform actual measurements.

Equipment:

• ADVANTEST R3361B Spectrum Analyser;

• vanilla miniVNA (no Pro, no lite, no tiny, ...nothing);

• VNA-J software versione 3.4.8;

• BNC adaptors from China (!);

All VNA calibrations are made for an OPEN over a 1-180MHz range with 6k points.

To make a prove of work I first calibrated the miniVNA for REFLECTION with a M2M BNC adapter followed by a F2F adapter. The calibration plan is expected to be located at the free side of that last adapter (far left end in the picture).

Cal plane for 50ohms load

 

Kenwood TS-430s: SSB RX with very low AF volume and S-meter stuck at S-0.

 Repair Brief – Kenwood TS-430s – bad SSB RX.

 

DISCLAIMER: the following instructions are provided only as a report of my hobby experience. In no way I am responsible of any damage you or your device can suffer by following this procedure. Lethal voltages are present in the device!! Qualified personnel only! You know what you are doing and you are proceeding at your own risk!

 

Symptoms (RX only):

• In USB and LSB low volume and no S-meter deviation.

• Strong (local) SSB station are demodulated OK and can be heard with very high volume setting. IF-Shift and RIT working OK as well as NOTCH.

• AM and CW are OK.

Findings:

• In USB and LSB, the ACG line (gate of Q13) stuck at 2.5V, no matter of signal strength.

• Q17 (what is it useful for?!) voltages: 2.6V all terminals as per schematics.

• SSB line goes high when USB or LSB are selected (as expected).

• On AM S-meter is well calibrated for S-0 and S-9.

• CAR signal present @305mV RMS in USB, CW (8.8314KHz) and LSB (8.8284KHz).
  It disappears in AM.
  

TOWER 5 Transistors Walkie talkies from the 60s - The ones that ignited my radio/electronics hobby.

Tale of my first transmission : 27.125MHz - CB Channel 14.

When I was young (late sixties, first seventies) I got a couple of black TOWER walkie talkies.
They were shiny and looked like rocket science objects.

My actual units

It wasn't long before I realized they weren't usable: communications with a friend were difficult, if not impossible, even between rooms.
On the other hand, however, one evening, I heard voices coming out of one of the radios. They were people who chatted about this and that using esoteric language...as well as coded words (CQ, QTH, QRZ, YL, 88, Roger, K, ...).
I tried to make myself heard, but no one could listen to me.
Suddenly, while I was desperately trying to make myself heard, (are you listening? Hello, ready, are you listening?...) one of those voices answered me. He greeted me, welcomed me and ... explained to me that I had a "super regenerative" radio in my hands and that it could simultaneously listen to many frequencies but only transmit on a single one. That's explained me why I was hearing many voices but I had difficulty make me listen.
After a few days I met that person: he was an OM with a shack that looked like a spaceship to me.
BINGO. Since then I have been CB for years and have become passionate about radio and electronics.
Eventually I also got an ham license.

A DIY bench RF step attenuator with Arduino and Aeroflex-Weinschel step attenuators

A while ago I made a bargain purchasing a couple of Aeroflex-Weinschel step attenuators (models 150T/11 and 150T/70) for 20EUR each.

The idea was to implement a bench step attenuator for my lab.

Here is the project.

Those attenuators offer serial and parallel digital interface. I choose to use the parallel interface protocol.

Each attenuator is controlled by 4 bits (a nibble), so, with the help of the following map, I built an Arduino sketch to drive the attenuators by a rotary encoder:

The table on the left simply lists all the wires coming out of the attenuators with color and function.