A few posts back I mentioned the LED dimmer switch on the Rodenberg pedals and while I was writing it, I was thinking about how to implement such a feature. The most obvious and simple solution is to put two resistors in series and bypass one of them with a switch as shown here. When the switch is open, the series combination of the two resistors will be limiting the current and the LED is dim. When the switch is closed, the larger resistor is bypassed and the current through the limiting resistor and the LED is increased so it is brighter.
An alternate way to make the dimmer mechanism is to put the resistors in parallel and use the switch to take the smaller resistor in or out of the circuit. When both resistors are connected, the parallel combination of the resistors is a lower effective resistance and the LED is bright. Toggle the switch and the LED dims since only the larger value resistor is in the circuit.
There is no advantage of this parallel resistor combination over the series method and either will do the job equally well.
Let’s experiment and find yet a different way to make the dimmer. We can do it by dropping the power supply voltage and this is accomplished with a series zener diode as shown here. The zener adds some extra voltage drop and therefore makes the LED dimmer when it is in place. Flip the switch to bypass the zener and the indicator will brighten.
Don’t have a zener to use? Put three cheap LEDs in series in the place of the zener to produce much the same effect.
One more way to create the dimmer is to use the switch to create a voltage divider. This requires an extra resistor so it’s not the best method but it works.
You can probably think of more ways to implement the dimmer switch. It is a simple feature to put on your next homebrew pedal so give it a try!