A-K Label on Intelligent Relay Bypass Board - Mistake?

[Dirty_Boogie]

What’s up with the LED A-K marking on the back of this relay board? The top of the board is marked for a 2N3904 transistor, but the back has anode and cathode marked for 2 of the holes. Just confirming this is a printing mistake on the back of the board, and I should only solder the 3904…?

 

[Robert]

The A/K markings are for the case where you want to mount an LED directly to the module, rather than use the LED on the main effect PCB.

You'd omit the 2N3904 and install an LED in the pads as marked. R2 becomes the LED current limiting resistor and the value should be adjusted accordingly.

For typical usage just ignore those markings.

 

[Dirty_Boogie]

Excellent, thanks Robert. Was hoping you’d respond.