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TheHWcave / Peacefair-PZEM-004T-

reverse-engineered schematics and interface software
MIT License
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pzem-004t and esp8266 with compatible level 3.3v #1

Closed 0neday closed 2 years ago

0neday commented 2 years ago

we know pzem-004t use 5v level for uart, and esp8266 ( nodeMCU ) use 3.3v level. I check your PZEM004T-orig.pdf, and this discuss , this commit

捕获.PNG change R8 to 10-100, so that when RXport get 0 level from esp8266, so that U3 pin 1 can get enough voltage and turn on U3.

Utyff commented 2 years ago

PZEM-004 works well from 3.3V without changing the resistor. I checked on CC2530.

0neday commented 2 years ago

thank you, I will test

0neday commented 2 years ago

@Utyff yes, 3.3v is work fine for pzem-004t v3.0 , maybe parallel R8 and R10 's resister is 500 ohm

rrelande commented 1 year ago

I assume we are talking about running PZEM-004T v3 with 3v3 on UART pin instead of 5V without modifying R8

according to theoretical calculations, it would barely work as the CT8217C optocoupler delivers a collector current of 5mA at saturation voltage. (5V 1k R7 resistor) This would mean that the limited forward current of 2mA may not open the optocoupler to saturation. A If of 4mA would indeed secure the optocoiupler opening.

that is theory, but is there any practical feedback?

rrelande commented 1 year ago

just checked on multimeter , using unmodified v3 and 3V3 on UART power supply to RX the current is 3.6 mA at 25 deg - this is more than theoretical calculation. it could be enough to saturate the optocoupler

so why make hardware modifications?