ESP8266 Community Forum

- Sun Sep 06, 2015 2:32 am #27904

Also, GPIO4/GPIO5 are default pins but any other GPIOs works well too, I'm personally using GPIO2/GPIO0 since they needs pullups any ways for the boot process

Good to know it actually works, I never tried. Very interesting for projects using only an ESP-01, so you can still use I2C on that one.

- Sun Sep 06, 2015 2:35 am #27905

If you have a look at the schematic, you'll find that this board is basically just a MCP23017 and a bunch of mosfets.
Since the MCP23017 will work fine at 3.3V, the only issue are the mosfets used (they really could have used better ones, especially at that price point). The 2N7002 n-fets used on the board have a max. threshold voltage of 3V (which is not ideal), but they should be good for switching about 50mA at 3V.
So as long as your relay coils draw less than 50mA (or you use additional FETs to drive them), you should be able to power the board with 3.3V and eliminate the need for a level shifter (and an additional 5V supply in your project).

It's not too easy to find a mosfet that has a low enough GthV in through-hole package. I use BS170, which is not ideal but works.

- Sun Sep 06, 2015 7:53 am #27924

Good to know it actually works, I never tried. Very interesting for projects using only an ESP-01, so you can still use I2C on that one.

Yes, it is working very well.

- Sun Sep 06, 2015 7:59 am #27925

If you have a look at the schematic, you'll find that this board is basically just a MCP23017 and a bunch of mosfets.

Since this board doesn't have the relays on the board itself, I don't see much advantage of it.
I would rather design myself a PCB that can have MCP23017 (at 3V as lethe said) driving directly an UNL2803 instead of that bunch of mosfets.