I’ve not played with microprocessors before was able to build a gadget which used an Arduino Uno pin 13 to trigger a relay using a relay (using the control pcb com-09096 and accompanying relay) but it turned out that the relay wouldn’t respond to digital pin 13. When the relay was connected to 5 volt supply, it tripped fine with 5 volts applied to the ctrl lead, but digital pin 13 only puts out about 2 volts and apparently isn’t enough to trip the relay. Everything else seems to work OK.
After some experimentation, I coded pin 11 to control the relay. When the Arduino turned “on” pin 11, it put out 4.88 volts, but that was not enough to trigger the relay. When I touched the control wire to a “5v” (measured at 5.0-5.1v), it would trigger. Does .1 volts make that much difference?
It depends on which 0.1 V difference. For each circuit and set of conditions, there’s a threshold below which it won’t work. If your threshold is 4.95 V, then the difference between 4.9 and 5.0 is critical. Contrarily, the difference between 5.0 and 5.1 is not.
How are you supplying the “RAW” voltage and have you tried different “RAW” voltages to your relay board? I took a look at [the relay board schematic. It appears that the coil receives a voltage that is the difference between the “RAW” voltage and the voltage drop across the transistor (available from the transistor datasheet, typically on the order of tenths of a volt). If you are feeding a “RAW” voltage that is very near or at the minimum voltage for the relay, then you are trying to operate the relay with a voltage below that at which it is specified to operate. Similarly, if your relay coil requires a current that is near the current capability of the transistor, than can be an interference.
As for the difference between Pin 13 and Pin 11: IIRC, Pin 13 has the on-board LED attached to it, so there’s a competing load.
If you need help finding the specific data for your components, post links to their datasheets and I’ll try to steer you in right direction.
If a digital pin isn’t putting out the full voltage (i.e. 5V for your Uno), it’s often because you forgot to set it as an output using the “pinmode” command.
Thanks, Trialex. Was in a similar situation with optoisolators. Couldn’t for the life of me figure out why my voltmeter was showing 0.0 for pin 13, but when I’d try 7 or 9 or any other pin, I was getting 2.2V at rest. Pulling my hair out trying to figure out if my bad EE skills had fried my Arduino/isolators-- Nope. Skipped a line. Silly. Thanks again.