Convert a momentary pushbutton to alternate action
This two-inverter circuit allows a momentary contact pushbutton
to provide alternate action: press on, then press off. Normally S1 will be off
and capacitor C1 will be charged to the same voltage as at the output of IC1a.
If S1 is momentarily closed, IC1a will be forced to change state (ie, low to
high or high to low at the output).
If the output at pin 2 changes to high, this will be inverted
by IC1a and fed back to pin 1 after S1 is released and so the circuit will
remain in the new state until S1 is pressed again.
If S1 is held closed (ie, pressed continuously), the circuit
will oscillate at a frequency determined by the time-constant of R2 and C1.
Brendan Ede, Nerang, Qld. ($30)
