I have previously reprogrammed a Sonoff S31 with ESPHome and had no problem. I am now trying to reprogram two more and I am failing miserably. I managed to destroy an S31 (not the two in question) by failing to move the power supply jumper on my FT232 adapter to the 3.3v position. That is not the problem here.
I actually purchased a second FT232 adapter after multiple failed attempts, thinking I may have damaged the original one when I blew up the on S31.
The problem I am seeing now appears to be a power problem and I do not know if there has been a hardware change in the S31s since I bought the first one.
When the S31 is connected to the FT232 adapter, with power and ground and the serial lines in the null modem arrangement, the USB port is not recognized, i.e. my Windows machine does not beep and the ESPHome programmer fails to find a valid USB port assignment. With everything connected except the 3.3v power lead, the USB port is recognized and the programming proceeds as normal, except that without power to the S31 there is no Tx back to the FT232.
I have tried stealing power from a different adapter in case the FT232 power supply was inadequate. No love there either. Measurement of the power leads shows the correct 3.3v present. Both S31 devices act the same way and when plugged into AC they are discoverable and work properly with eWeLink.
Update:
The 3.3v power was indeed what was causing the USB port to not be recognized. Connecting a bench power supply to the power leads fixed that problem. Self powering the S31 from the FT232 adapter did not work on any port on my laptop or tablet. Powering from an AC outlet with USB ports caused the blue LED on the S31 to light, it never did when connected to the laptop.
That is one problem solved. Still cannot communicate properly with the ESP chip the S31. I get messages like ‘Failed to connect to ESP8266: No serial data received.’ or ‘Failed to connect to ESP8266: Invalid head of packet (0x08): Possible serial noise or corruption.’
Is it possible that Sonoff has changed the ESP chip to another type? It is not possible to see the chip without removing the plastic bottom cover. It looks like this requires desoldering the female AC connector pins.
More Update:
I have successfully reprogrammed the two S31 devices. Unexplainable resolutions of problems really bother me.
The problem with apparent insufficient power from my two TTL adapters was causing the computer to not sense the USB device. Initially I thought this was a computer problem although my tablet exhibited the same problem. Using different USB power sources did not present the same problem, i.e. the USB device was recognized. This gets a bit muddled as my other CH340 adapter did not present the same problem. My guess is that the inrush current was excessive for the DSD Tech SH-U09C adapters making me reluctant to recommend that device.
I was able to complete the reprogramming but only after finding by some research that others were having this problem and that the solution was a reversal of the Rx and Tx lines. While this seems to me to be nonsensical, it did work. Normally you expect to cross connect the Rx and Tx (null modem). Perhaps this is simply a matter of labeling. Does the label define the function of the pin or does it indicate where the Rx and Tx should be connected? Strangely enough the one of the DSD Tech adapters lit the Tx LED when the computer was attempting to connect while the other one lit the Rx LED. Now these devices are completely programmable and the sense of these two lines could be reversed between the two adapters.
In any case the job is completed and I will be looking for a more capable USB/TTL adapter.