SSR: inline resistor required?

Components & Accessories Power
1

Hello – I was curious about using these SSR’s with an Arduino (Zero): https://www.sparkfun.com/products/13015

…is it as simple as connecting arduino GND to the negative terminal and an arduino output GPIO pin (configured as pulldown) to the positive terminal, then setting pin to high when wanting the SSR to turn on, or do I need any intervening components?

The “implementation hints” in the data sheet show a PNP transistor setup feeding the + input, and I’ve also read that with some SSRs you need an inline resistor, etc., so I wanted to confirm.

Thanks!

2

With that particular SSR, the current limiting resistor for the input LED is built in. A clear indication of that is the input voltage specification of 3-32 VDC, printed on the module.

3

Thanks!

4

Just in case anyone else finds this – these SSRs apparently need more current (5mA) than the GPIO pins can deliver (2mA, IIRC), so a separate power source and transistor/resistor is needed (AFAIK). Bummer. :slight_smile:

5

clepsydrae:
Just in case anyone else finds this – these SSRs apparently need more current (5mA) than the GPIO pins can deliver (2mA, IIRC), so a separate power source and transistor/resistor is needed (AFAIK). Bummer. :slight_smile:

According to https://store-usa.arduino.cc/products/a … edStore=us, that board can source 7 mA per pin.

6

Thanks… I’m in over my head here, so my info might be way off, but my confusion might be due to a potential issue where the Zero GPIO pins don’t reach their spec’ed output current:

https://github.com/arduino/ArduinoCore-samd/issues/158

Thread here: https://forum.arduino.cc/t/are-the-zero … t/404930/7

…maybe this explains what I’ve been seeing. Investigation ongoing. :slight_smile:

7

Interesting. If this thread is correct and it’s actually configuring the outputs with a 2 mA limit, some people posted functions that you can use in place of pinMode that sets the current limit up to 7 mA.

https://github.com/arduino/ArduinoCore- … -288800192

If you add that function to your sketch and replace pinMode(pin, OUTPUT) with pinStr(pin, 1) it will enable the pin as output with higher current.

Here’s another:

https://github.com/arduino/ArduinoCore- … -584231347

If you add that function to your sketch and replace pinMode(pin, OUTPUT) with setHighStrenghOutputPinMode(pin) it will enable the pin as output with higher current.

8

Yes, thank you! I was going to try a workaround (same idea) from the forum thread:

PORT->Group[g_APinDescription[7].ulPort].PINCFG[g_APinDescription[7].ulPin].bit.DRVSTR = 1;

9

…and that worked! Turns on the SSR fine now.