/diy/ - Do It Yourself

>>1216893
>using straight R-C to produce several hours long delays
>requiring a special comparator with internal hysteresis to avoid output chatter
>relying on comparator's output current limit to drive the BJT
>worrying about comparator's input current, but ignoring capacitor's leakage
>no limiting resistor in series with P
>math suggests no overdriving of BJT
>dragging logarithms everywhere, when you could simply choose R2/R3 to give t=P*C or some other convenient value

Since large resistors and capacitors seriously suck, it is more practical to use a higher frequency oscillator and divide the frequency down. Since this is a common problem, there are ICs like 4541. It even requires (slightly) less components. Pic related has all kinds of extra shit, like extra ranges, though.