I am using some 12 volt relay boards from ebay that do not seem to match schematics I can find , Including what came with it.
I have attached what I have.
The boards come with the input R1 resistors as a 10k value. With an Arduino Digital High this gives around 190 u amps through the indicator LED and the chip emitter diode. This is not enough to saturate the output transistor and results in only 6.7 volts across the coil.
What I wound up doing is replacing the R1 resistors with 1k. This gives 1.90 ma through the indicator LED and the chip emitter diode. And fully turns on the relay.
Has anyone else run into this ?