ka7oei

Another site visit was made (not by me - it's a 120+km drive each way) - with enough time to take things apart and do a more thorough investigation:

• Kiwi #2 was found to have low supply voltage: We found that the power cable had been crushed/stretched (but not shorted) and it had rather high resistance: With 5.05 volts at the power supply, there was only 4.35 volts measured at the PCB connector. We ended up removing about half of the power cable for the time-being as we no longer trusted it. I'm guessing that #2 went offline coincidentally a few days before the others, largely for this reason.
• As per suggestions, we did check the power supplies. Even under start-up load, nothing seemed amiss: The supply for Kiwis 1-3 is a pair of diode-OR'd 3 amp-rated linear supplies (International IHB5-3) and couldn't find anything strange about it (about 4.95 volts at the Kiwi PCB when it's up and running): We were wondering if one of the two supplies had crowbarred - but this wasn't the case. (We have had one of the two supplies crowbar in the past due to lighting and it was still enough to run the three Kiwis as the actual fold-back current of these 3 amp supplies appears to be a bit north of 4 amps).
• I believe that the power supply for units 4 and 5 is a 4 amp switcher (with lots of added filtering on the AC input and DC output to avoid RFI and a lot of bulk capacitance on the output for impulse loads).
• Just to be safe - and since it had been a problem child for a long time (even before it was used on the current, dual 3-amp ORed supply) we backed up the newest KiwiSDR (#5) and put the image on KiwiSDR #2, just in case something was amiss.

The reason for Kiwis 3-5 to do what they did all at the same instant (except for #1) when conditions could not be ascertained to be quantifiably different than in the past when updates were done is unknown - but the reason for #2 is quite clear, now.

• * *

On the next "official" site visit (where there are several of us with a carload of gear and parts) I'll bump up the output of at least the dual 3-amp supply to about 5.25 volts - something that has been suggested here before.

Thanks for everyone who made comments and suggestions.

73,

Clint, KA7OEI

Although intended for monitoring mains voltage, I did a somewhat similar thing using the ESP8266, described here:

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An ESP8266-based Temperature, Humidity and Line Voltage monitor

https://ka7oei.blogspot.com/2020/06/an-esp8266-based-temperature-humidity.html

Figure 1: The completed Temperature/Humidity/Line Voltage web server/telemetering device.  The remote temperature/humidity sensor is th...

The source code is linked, and making it read supply voltage rather than mains voltage would be trivial. The '8266 has only a single A/D input, but the addition of a simple analog MUX chip like the 4051 would easily expand this to 8 inputs - although one would probably want to level-convert the MUX drive to 5 volt logic (e.g. an NPN and two diodes).

* * *

If a network connection isn't in the cards (the ESP8266 has 2.4 GHz WiFi only) this also includes a Morse beacon that telemeters the information - in this case, on 10 meters: This was added so that telemetry could be seen by anyone interested, but also so that we could still receive it should the WiFi connection drop for some reason.

* * *

Finally, the same, basic low-power TX could be driven by a PIC or Arduino, of course to produce Morse telemetry.

To get back to an aspect of your question: I suppose that a BBG GPIO pin with an A/D input would be available, but I chose to leave the KiwiSDR unit unmodified - both for practical reasons (a spare could be swapped out) and also to avoid the possibility of conducting undesired signals in/out of the chassis (e.g. static, RFI, lightning, etc.)

73,

Clint, KA7OEI