ESP8266 Community Forum

- Thu Mar 17, 2016 1:11 pm #43424 I'm sorry, must have somehow swapped them previously. I checked several times. I'm reading:
3.3v - ra=4mv
5v - rb=483mv

Sorry for the goose chase there. I'm not sure how I did that.

ra stays at 4mv when the blue is disconnected.

- Thu Mar 17, 2016 1:34 pm #43426 No worries, this makes sense now. When you cut the 5v power the relay opens up because there is nothing to energize it. The optoisolator remains turned on with a fairly low current because it doesn't take much to power the internal LED as well as the indicator LED. By the way, the Songle SRD 05VDC SLC datasheet lists the nominal coil supply current as 71ma, Sainsmart says 15-20ma and you and I measured 45-50ma. I would say Songle is being fairly conservative and Sainsmart rather optimistic in what it takes to drive these. Good luck with your project!

- Thu Mar 17, 2016 6:09 pm #43440 Looking at the photo of the relay board on Amazon it looks like there's an indicator LED in series with the Opto Coupler LED. That's pushing the ability of a 3V3 GPIO to provide enough forward voltage to get them both to light.

Unless I'm missing something, all the talk of relay coil current is a red-herring. The Opto Coupler transistor output handles that for you. The task is to get the LED inside the Opto to turn on the output transistor. Is there a schematic for the relay board?

Edit: Is this it? If so there's a resistor in series with the two LED's as well so I'm thinking 3V3 isn't going to be enough. Maybe short out the indicator LED and see if the GPIO will pull enough current to fire the Opto.

- Thu Mar 17, 2016 7:55 pm #43448 I actually figured out my issue. Somehow I misread my meter and instead of 40ma it was .4ma. The huzzah does a fine job of driving the opto with 3.3v.

It's a new meter and I need to be more careful reading it