/diy/ - Do It Yourself

>>1664020
The 555 can do 40 minutes. The time is 1.1RC so 10MΩ and 220µF will get you 2400 seconds. The optimal IC for long time delays is the 4541 and another option is the 4060. Both have a built-in clock oscillator and a binary counter.

>>1217661
You need at least a 9V supply for the auto-reset function to work. Earlier in this thread someone confused 470nF (=0.47µF) and 470µF. I'd suggest you try manual reset, output initially high, recycle mode and n=13. LED should blink or flicker. Calculate expected frequency and compare result.

This is not critical but I think RS is way too small, it should be at least 2*RTC. The reason is that the peak voltage at pin (3) exceeds Vdd and Vss and activates the protection circuitry which speeds up the clock generator.