Relay problem

[CNCDevil]

Hi :-)

I'm trying to get a SSR (3-32 VDC) to work with my BOB. The outputs are opto-isolated.
I connect GRD to minus and output 17 to plus of the SSR terminals, but the 5VDC won't turn it on. I have tried to measure the voltage across the SSR and I see that the voltage is below the threshhold value, around 2.7 VDC. When I connect the relay directly to my 5VDC source it works properly. When I measure the on/off state of the output, the voltage is 5.2/0.14 VDC.

I then tried to make it work with a 2N7000 Fetlington. Gate to output 17, Source to minus of SSR and Drain to GRD. The SSR plus-terminal is connected directly to the +5VDC source. Now the SSR is turned on no matter what I do.


Any suggestions what to do or what have I made wrong here?


Thanks,

Brian

[Al_The_Man]

Your 2N7000 source pin1 should be connected gnd and the drain pin 3 to the SSR-.
Al.

[CNCDevil]

I have actually done it this way, but wrote it wrong. I have tried to replace it also. Any ideas? I can't see why it should't work. When I look at the flat face with the pins down, it should be S, G, D right?

[Al_The_Man]

If you hold it in front of you with the pins facing you and the flat side down it is 1 to 3 from right to left.
It is made for TTL interfacing and in fact it is recommended that a 1 k pull up from gate to +5v be used if being driven by an open collector driver.
Al.

[CNCDevil]

Thank you so far Al, it could very well be that pull up resistor that makes it work. I'll return later with some more experience.

Brian

[Al_The_Man]

Also check the gate voltage when switched on & off by the port.
Al.

[CNCDevil]

I tried with 1K, but it was still working too well. A 10K resistor did the job.

Thanks :-)