Max current per I/O pin..

Hello all, I see the max current per I/O pin is 40mA. I'm wishing to drive a SCR that is spec'd at 35mA gate trigger. Since the SCR will be triggered all the time to conduct, 35mA seems a bit close to the max for comfort.

Is it possible to parallel 2 or 3 I/O pins and them share the load? OR is an interfacing transistor on order? Sure would like to parallel I/O pins if that will work. Timing is not critical, I'm using the SCR to turn voltage on for power supply, then if an alarm condition is detected, remove trigger to remove voltage from output of power supply.

Thank ya'll for any help and suggestions.

Ken H>

In theory you could wire to two or more output pins in parallel, but in practice it's a real risky proposition. One would have to make sure all the connected output pins always switched at the same exact time, not using individual digitalWrite commands, but rather using direct port accessing and insuring the shared pins were on the same port.

Too much chance of pin damage while testing such a program I would think. And while 40ma is the max current, the manufacture recommends 20ma for continous usage. So you are probably better off using a transistor to switch the gate of your SCR.


Thanks for the info Lefty - I had looked thru the m168 datasheet but missed the continuous rating of only 20mA. Since I don't have any idea how to do "Direct port accessing" - I guess I'd better just use a transistor to switch.

That's why I was waiting to etch the PCB just to be sure of what I needed to do.

Thank you for the guidance.

Ken H>

Just to confirm the transistor switch to use to trigger the SCR - I have a NPN switching transistor with a Ic rating of 200mA. I think I would put the base to the Arduino output pin with a 1K resistor in series. Connect 5 vdc to the collector, then connect the emitter to the gate of SCR.

When the I/O pin was written HIGH, that would put 5vdc to the gate of the SCR turning it on. Does that sound correct?

Thanks for any and all help,

Ken H>