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

Hello all,

I've been meaning to make this for a while - it's a laughably simple project (for all but the electronics simpletons like myself).

So, I'm going to base my circuit on this one:

http://www.555-timer-circuits.com/flashing-led.html

http://www.555-timer-circuits.com/im...-schematic.gif

...except I'll be using a 12v PS and one of these instead of an LED:

Attachment 21472

R1 and R2 control the speed at which the LED flashes - or rather (I'm hoping) the solenoid will open and close - as it is, the led flashes rather quickly - I'm planning to replace these two resistors with a couple of linear pots so that I can adjust open/close times - any recommendations for pot values I should be looking at..?

Also, the cap value? As I'm using a 12v supply will I need to change the cap - what difference would a different value make to this circuit?

Finally, will this work..?! Have I correctly assumed that R1 and R2 are independently controlling open/close times?

Any advice appreciated..!

Wal.

Wal I have a 12V solenoid air valve if you want it give me a shout. I think you might need a fly back diode across it.

Cheers Clive,

I'll drop you an email. You might need to explain the fly back diode to me... :stupid:

Wal.

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

Attachment 21473

John

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.

Quote:

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Originally Posted by 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.

---

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

Cheers Clive..!

That's me being dumb again...! :whistle: 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.

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
Attachment 21474

Attachment 21475



John

Quote:

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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

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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

Quote:

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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

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...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.