I recently bought one of these:-https://library.e.abb.com/public/9e.../Royce Thompson Astro Nova City datasheet.pdf
and I found that it was quite easy to get it to crash, with the display locked up, and no function at all.
I looked at it a bit more today. It's got a transformerless power supply, with an electrolytic capacitor running at around 40 V There is a 3.3 V supply to the electronics that is kept going with a rechargeable battery. It seems to crash when the mains power is removed, and the electrolytic capacitor drops below the voltage. Once it has crashed, the electronics needs resetting by waiting for the battery to run down, or by opening up the timer and temporarily disconnecting the electronics from the rechargeable battery.
It looks like the 3.3 V supply dips and upsets the microcontroller, and it seems to be worse when the backup battery isn't well charged. Perhaps with a fully charged battery, the microcontroller would keep running correctly when the mains is removed.
There doesn't seem to be a low voltage reset, or a watchdog. Disconnecting the power and waiting for the battery to run down seems to be the only option, and with a 4 year battery life, that could be tedious.
Is the circuit as poor as I think it is?
and I found that it was quite easy to get it to crash, with the display locked up, and no function at all.
I looked at it a bit more today. It's got a transformerless power supply, with an electrolytic capacitor running at around 40 V There is a 3.3 V supply to the electronics that is kept going with a rechargeable battery. It seems to crash when the mains power is removed, and the electrolytic capacitor drops below the voltage. Once it has crashed, the electronics needs resetting by waiting for the battery to run down, or by opening up the timer and temporarily disconnecting the electronics from the rechargeable battery.
It looks like the 3.3 V supply dips and upsets the microcontroller, and it seems to be worse when the backup battery isn't well charged. Perhaps with a fully charged battery, the microcontroller would keep running correctly when the mains is removed.
There doesn't seem to be a low voltage reset, or a watchdog. Disconnecting the power and waiting for the battery to run down seems to be the only option, and with a 4 year battery life, that could be tedious.
Is the circuit as poor as I think it is?