555 timer circuit to control 12v solenoid air valve (for intermittent bursts of air).

[john swift]

I would expect the NE555 can not provide enough current to operate the
solenoid valve without the addition of a high gain power transistor
like the TIP122
the 1N4001 across the coil is the flyback suppressor diode
when the transistor is switched on the diode is reverse biased so it does not conduct
when the transistor switches off a large back emf is produced
the diode provides a path for the current to flow instead of
driving the transistors collector more positive than the positive supply



John