Digital I/O, proto board, lower voltage than expected


I'm having difficulties trying to trigger solid state relays with the industruino D21G proto. I only seem to be able to get an input tension on the relays of 2,70V, and not 3,3V. Tried a pull-up resistor on the digital out to 5V, I do get 5V with no load attached to the industruino, but still 2,70V when connected to a relay.

I took everything out of the circuit, and it's the same with 2 different relays. There are no other components than the relay, the industruino, and the pull up resistors I added (it behaved the same before and after adding the resistors).

Does that ring any bell ? A regular arduino uno has no issue whatsoever driving these relays with the same wiring...

Guillaume Couturier
Guillaume Couturier
| 1 1 2
Asked on 4/3/18, 1:04 PM

Dear Guillaume, Can you please tell me which pin you are using to drive the SSR? Can you please tell me the model number of the SSR? What value of pull-up resistor are you using? Best Regards, Loic

Loic De Buck
on 4/4/18, 7:04 AM

Dear Loic, Thank you for your answer, and sorry for not being more specific right away. Here are the details : - I'm using pins D11 and D12 (two SSRs, but same behaviour with only 1 of them). - The model of SSR : Crydom DR48D12 ( - Pull-up resistors value : 10kOhm

Guillaume Couturier
on 4/4/18, 9:38 AM

I realize that when I said "two SSRs, but same behaviour with only 1 of them" it was a bit ambiguous as one could think that it worked ok with one of the two SSRs. It doesn't : it doesn't work with one SSR, doesn't with the other SSR, and doesn't when both are wired. So it's not about a faulty SSR.

Guillaume Couturier
on 4/4/18, 3:32 PM

Hi, I ended up buying a new industruino proto to be 100% the one I had wasn't faulty, but no, it's still the same. I kept it as new, didn't solder anything on the proto board, disconnected everything but one SSR, and I still get 2.7V at the SSR's input instead of 3.3V (I know 3.3 isn't enough for this SSR, it's just that I didn't want to solder pull up resistors to 5V to check the board's behaviour as new).

Guillaume Couturier
on 4/7/18, 11:46 AM

The high turn-on voltage range for this SSR (4V-32, 24V nominal) might indicate to the problem. Can you please check how much current SSR input is drawing when connected directly to a 5V source (connected to 5V supply, not GPIO pin) ? It is possible that the GPIO of the PROTO is not providing enough current for it to turn on. The 3.3V GPIO of the PROTO goes through a bidirectional level shifter to support 5V output with pull-up. I know it is possible to increase the drive current with some low level register settings on the MCU, I can look for the correct command to increase the current of the specific pins that you are using (not recommended to increase all pins as it could damage the MCU).

Loic De Buck
on 4/8/18, 7:38 AM

Hi Loic, You're probably right. Time was becoming critical so I ended up switching the industruino with an arduino uno though, it's too bad because the screen and form factor of the industruino was perfect. Nevertheless, thank you for your help.

Guillaume Couturier
on 4/8/18, 5:55 PM

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Asked: 4/3/18, 1:04 PM
Seen: 1747 times
Last updated: 4/8/18, 5:55 PM