Actually, DIYMall finally updated their AS608 Amazon page with better documentation. It’s too late to give it a try tonight, but I will definitely work on it again tomorrow. For now, the pinout on this particular variation:
Pin Color In/Out Signal Description
--- ------ ------ ------ -------------------------
1 Blue Input Vtouch Touch sensor power input
2 Yellow Output Sout Touch sensor output
3 Red Input Vin +3.3VDC
4 Green Output TXD Transmit Data
5 White Input RXD Receive Data
6 Black Ground GND Signal and power ground
And this morning, she’s up and running. Got the chip connected, password initialized, and ready to rock and roll. The issue was the erroneous information originally provided by DIYmall (in my initial post above).
With RXD and TXD properly connected, it’s now flashing as expected and reading fingerprints.
Spoke too soon. Apparently, this AS608 from DIYmalls.com is defective. While it WAS working, the very next firmware flash, it refuses to communicate again.
Re-checked my soldering and connections with the ESP8266, no issues there. Switched to a LOLIN D32 ESP32 board, which would not load firmware when the reader was connected. Disconnected reader, loaded firmware, reconnected reader, rebooted ESP32, errors galore on boot loop. If I had to guess, I’d say this reader is sucking down a LOT of current and causing issues with the ESP32 board.
After reading reviews of other non-brand-name AS608 sensors on Amazon and other sites, they pretty much ALL complained of dead shorts and non-functional units. I can say, for that one single boot cycle when the reader lit up, it was working just as it should. So the AS608 is compatible with the ESPHome driver.
All the documentation I’ve found says the AS608 only draws 60mA maximum. But I think another issue is most D1 mini clones supply only 150mA through their 3v3 port, due to using a lower capacity LDO/regulator. I’d guess this design shortfall, plus a higher than stated current draw is causing the issue I’ve observed. The solution is to hack a higher-current AMS1117 LDO/regulator onto the D1 mini clone board.