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

[Wal]

Cheers John,

I spotted this online earlier:

http://www.robotshop.com/uk/adjustab...ering-kit.html

Might do the trick, although the output voltage is 24v as opposed to the 12v the solenoid wants.

Cheers for the additions to the diagram, I'll post my results if I make one..!

Wal.

[Clive S]

Cheers John,

I spotted this online earlier:

http://www.robotshop.com/uk/adjustab...ering-kit.html

Might do the trick, although the output voltage is 24v as opposed to the 12v the solenoid wants.

Cheers for the additions to the diagram, I'll post my results if I make one..!

Wal.

Wal See your email. It is the contacts that are rated at 24v 3A

[Wal]

Cheers Clive..!

That's me being dumb again...! If it helps anyone else reading this:

The output is the relay contacts RATED at 24V 3A and not outputting anything. ie the relay is just a switch that changes state. So the control circuit runs off 12V and you can run the air valve off 12v through the relay.

Thanks again Clive!

Wal.

[john swift]

Hi Wal

the Velleman kit should make it easier

looking at the circuit it runs of a 12V supply - ideal for your solenoid valve (don't forget to add the diode across the coil)

MK111 kit






John

[cropwell]

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]

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]

...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]

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:



Wal.

[Clive S]

Glad you have it fixed up and running Wal. Have you put a grommet around the red/black wires out of the tin ? to stop chaffing.