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

**cropwell** · 01-05-2017

Originally Posted by 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

John

The 555 can source or sink up to 200mA, so should be OK to operate most relays directly. The 555 is a useful timer chip, but I tend to use arduinos, especially for really long delays.

Cheers,

Rob

**A_Camera** · 02-05-2017

Originally Posted by cropwell

The 555 can source or sink up to 200mA, so should be OK to operate most relays directly. The 555 is a useful timer chip, but I tend to use arduinos, especially for really long delays.

Cheers,

Rob

...but 12V 6.5W is over 500mA, so if he is going to use the solenoid on the picture he needs a transistor, or a small relay in between the valve and the 555. The 555 is OK for small relays but not for solenoids.

**cropwell** · 02-05-2017

Originally Posted by A_Camera

...but 12V 6.5W is over 500mA, so if he is going to use the solenoid on the picture he needs a transistor, or a small relay in between the valve and the 555. The 555 is OK for small relays but not for solenoids.

I did not mention a solenoid

**Wal** · 12-05-2017

Right, got this made now. It's flung together into an empty air-rifle pellet tin I had lying about, but it seems to work alright...

I eventually used this circuit.

...you can get essentially the same thing for half the price here - I assumed at the higher price that this was pre-soldered - it wasn't..! The two pots that control the interval/pulse are a bit sensitive, but otherwise it's a decent enough kit and very easy to put together. I didn't need the fly-back diode after all.

Thanks to Clive for suggesting the switch to over-ride the circuit and keep the air on continuously - useful and pretty much a necessity..!

Here's a vid of it in action:

And for fellow electronics dunces, here's a diagram of how it went together: