LCD and SSR questions

[rocketbob]

Thanks for putting this nice project up on github!

Question: as I understand the maximum gate current on an IO pin on the ESP32 is 12mA. Is that enough to drive the SSR? In my case I have two heating elements in my kiln and will have to drive them from separate pins because I don't think the ESP can source enough current to drive both from one pin.

[Saur0o0n]

As I understand specs, fully safe (safe to board, chip etc.) current from IO pin is limited to 12mA, but it can get higher as 50mA - I wrote this to make information complete.
Now to the problem.
I also have two heating elements, but I control them with single 40A SSR, like you can see it here:
- more here.
On the other hand I've never checked true power requirements for SSR (and they can vary a lot) - this one should have 12mA, but for 12V, so for 3V it's going to be much more - I'll have to measure.
But it has been working for a while, so I guess it won't kill ESP immediately - perhaps in time :)

Anyway, since I've already provided +5V (directly from power supply) to relay box for EMR relay, clean solution would be to use small transistor, to drive bigger current. I guess for example 2N3904 and some current limiting resistor would be enough.

But, If you would need two separate SSRs - it's going to be extremely easy to do - just let me know.

[Saur0o0n]

Ok, so I've tested mine SSR and it draws max 8,73mA (at least this is how much my multimeter can measure in MAX mode - I don't know it's frequency). I've looked also at some different specs for Fotek SSRs - and some says MAX 12mA, some says 7mA at 12V, and also I definitely don't have original Fotek :).
So long story short - one SSR is safe, two SSRs well.. should be safe, but better is to:

• drive two(more) heaters with single SSR (if it's in range of SSR specs - for Chinese 2x the specs ;) ).
• add an transistor (like 2N3904) and resistor (330R / 330 Ohm should limit current to 10mA) to drive two(more) SSRs
• use additional GPIO for another SSR (I'll add it)

[Saur0o0n]

I have another idea - quite easy to implement :). You could use logic level converter module like this.

This way you can have up to 8 SSRs - driven with single GPIO (with this chip/board). Just connect one side VA to 3,3V and ESP32 pin 19 to all A0-A8 gates. Then on the other side connect +5V to VB and B0-B8 pins to SSRs you have. This chip can (according to specs) provide up to 50mA of current on single pin.