As part of the final for Energy, Rashida and I are dealing with 555 timer circuits and intermittently power cycling a rover. For this class I’d like to create a modular 555 timer circuit that is A) adjustable in its cycle, and B) modular in its use.

Here are the schematic and calculations for the 555 timer circuit. Rashida uses a different configuration of the 555 timer, and is planning on allowing the resistors and capacitor to be adjustable.

I plan to sacrifice some of the adjustability in favour of a mostly SMD (and thus smaller) board. To allow for a bit of flexibility I will use a potentiometer as R2, and include two selectable capacitors.


R2: As seen here, R2 affects the time off in relation to R1 (time on). Unfortunately with the basic setup the time off can never be more that 50% of the duty cycle. Rashida’s solution is to us an ‘improved’ 555 timer circuit, my solution is to use a logic inverter in front of the relay.


  • 47 uF capacitor
  • 470 uF capacitor
  • Transistor (or logic inverter)
  • 500K resistor
  • 500K potentiometer
  • Toggle switch
  • Relay