Robby Kraft (mostly Robby) and I threw this 555 circuit together on Wednesday night (2/25/2011) out of parts we had. Robby has an extensive and well-sorted box of capacitors and loves playing with 555s, two things which made making this circuit easy.

We started from this 555 timer that Jeff threw on the mailing list. We wanted to make a circuit diagram so others could repeat it easily, and make the time adjustable.

Robby immediately found a great 555 Timer Calculator after a minute or two of searching on Google, and we plugged in values into the calculator, and tried out different combos of capacitors, resistors, and potentiometers until we had something we liked. Total project time- about 1.5 hours, not counting collecting the parts because they were things we had already.

the parts you'll need can be easily found at Radio Shack, online at Digikey, or my favorite local supplier, URS Electronics in Portland.

You need: 555 DIP timer 5VDC Relay 100μF capacitor 100kΩ potentiometer (the pot we had on hand was much larger, physically, than you want. ) 47K resistor PX28A 6V Photo Battery

here's what we got:

Changes to Make Use a much smaller, screwdriver turned Potentiometer (already linked to in "Supplies" above.