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Wal
29-04-2017, 12:32 PM
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/images/circuit-flashing-led-schematic.gif

...except I'll be using a 12v PS and one of these (http://www.ebay.com/itm/1-4-2-Way-Normally-Closed-Pneumatic-Aluminum-Electric-Solenoid-Air-Valve-12V-DC/182078724061?_trksid=p2047675.c100623.m-1&_trkparms=aid%3D2220072%26algo%3DSIC.MBE%26ao%3D2% 26asc%3D40130%26meid%3D9aa323a1605e4b61a2614d30c79 9a41f%26pid%3D100623%26rk%3D1%26rkt%3D6%26mehot%3D pp%26sd%3D182545090588)instead of an LED:

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.

Clive S
29-04-2017, 01:55 PM
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.

Wal
29-04-2017, 01:59 PM
Cheers Clive,

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

Wal.

john swift
29-04-2017, 02:44 PM
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

21473

John

Wal
29-04-2017, 05:38 PM
Cheers John,

I spotted this online earlier:

http://www.robotshop.com/uk/adjustable-interval-timer-soldering-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
29-04-2017, 05:47 PM
Cheers John,

I spotted this online earlier:

http://www.robotshop.com/uk/adjustable-interval-timer-soldering-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
29-04-2017, 06:05 PM
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.

john swift
29-04-2017, 06:36 PM
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
21474

21475



John

cropwell
02-05-2017, 12:50 AM
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, 01:18 PM
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, 01:24 PM
...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, 02:58 AM
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 (https://tinyurl.com/mavfa43).

...you can get essentially the same thing for half the price here (http://www.maplin.co.uk/p/velleman-adjustable-timer-solder-kit-vt27e) - 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:


https://youtu.be/N3M1x4GMAtw

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

21621

Wal.

Clive S
12-05-2017, 09:49 AM
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.

Wal
12-05-2017, 10:10 AM
Hi Clive, I didn't have any grommets to hand, so I've hot glued (around the holes) all wires going in/out... stops 'em moving about.

Wal.