Momentary lockout Solenoid

[syntax_x]

Hello, New user here with a simple little problem.


**broken link removed**

This is the circuit I am working with, it emulates the recoil of a pistol and allows a signal from the trigger to be used. (the black square is a relay..)

The problem I am having at the moment is if the trigger is held down, the solenoid stays engaged, no-brainer right?

So I am trying to make the solenoid receive power for only the duration needed to send it into a fully engaged position.

That way the solenoid recoils before the trigger is deactivated.

I can post up some videos of my progress so far if it helps.

 

[Mr RB]

Firstly, Hi and welcome to the forum.

And thank you for posting clear information on exactly what the circuit does and providing your circuit diagram! Lots of first-time posters leave out critical information.

OK, your diode is connected wrong. it should be connected across (parallel with) the solenoid coil, woth the diode ANODE (white stripe) at the + end of the solenoid coil (not the GND end). After that your diode will do it's job, and protect things against the solenoid induced back-EMF spike.

Next, to get the "one shot" result you need, there are a few solutions involving monostable timers, which adds complexity.

You might be able to get away with a simple solution, and just put a large cap (2200uF) in series with the solenoid wire (where you show the diode in post #1).

The cap will make a current pulse while it charges, that will "fire" the solenoid. Then when the cap is charged there is little/no current and the solenoid will drop out. That will require a resistor across the cap, to discharge the cap when the user is not firing. The discharge time will need to be shorter than the time between user firings. Maybe try a 1000 ohm resistor, but have a few values handy if it needs a higher or lower value resistor.

 

[WTP Pepper]

Using caps is guessing when the solenoid is fully engaged. I would use something like a simple magnet on the solenoid triggering a reed switch to disable the drive current to the solenoid.

It then makes it a closed loop control system where you definately know the solenoid has engaged.

 

[Mr RB]

That will oscillate!

 

[WTP Pepper]

With a bit of careful design with a few flip flops, it won't.

 

[alec_t]

How much current does your solenoid draw at 24V?

 

[syntax_x]

Hmmm... It seems the Administration team did not like my response...
Lets try again (for the 3rd time...)

Thanks for the warm welcome Mr RB. Nice to have a long time member give me a hand straight up.

Concerning the diode, yes i had it in the wrong spot, the solenoid actually came with 2 diode already inplace, 1 is where you stated.

I have looked into using a 555 timer in momentary mode as a one shot, but im not sure where to start with resistor and cap values, and im pretty sure ill need a pot to tune the response rate.

WTP Pepper, thankyou for your input, its greatly appreciated, but my thoughts were the same as Mr. RB, i feel it would oscillate.
I'm sure with a few flip flops and the magnetic reed it would in theory work, but the solenoid itself has a very violent action and would probably introduce different forms of interference and false inputs.

I WILL post up some links to videos on what i have done thus far.

I would like to add that I am not a student, and that this is not for profit of any kind, except my own enjoyment and maybe others.
If i manage to get this working ill be posting a write-up on how to, and anybody who has helped here will be getting the credit.

Im just a guy with a soldering iron..

Cheers again on the input thus far , ill check the current draw @ 24v right now alec_t.

 

[syntax_x]

If Admin allows it, here is a more in-depth picture of my project.

 

[syntax_x]

When the solenoid is first engaged the current pull is 1.4 A. If i keep it held it slowly drops past 1.2A. Didn't hold it on any longer than that.

 

[alec_t]

What is the foot pedal for?

 

[syntax_x]

For this

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[alec_t]

Here's a suggested driver for the solenoid:

 

[syntax_x]

Hey alec_t, Did you just throw that together for me?

Thanks champ!

2 questions, what is m1?, and what does the pot change?

 

[Mr RB]

For this

**broken link removed**

Nice machine! I feel a bit silly now, my original comments were with the idea to keep the parts count down, as I thought you were fitting this inside a small device like a laser tag grip.

 

[syntax_x]

ok so i got all the parts for Alec-t's 555 circuit, just wanted to make sure the caps i bought will work for this.



**broken link removed**
**broken link removed**

 

[alec_t]

Those caps will be fine.

 

[syntax_x]

Cheers Roman, I'm pretty happy with the cab myself

alec-t, ive built the 555 circuit but I'm pretty sure M1 on your diagram is a transistor. Im not sure what to do there...sorry.

hopefully i wired the pot up correctly too, i soldered to the outside legs, which is wrong hey, i should of used the middle and left leg i think...

 

[syntax_x]

My bad, just wired up the pot correctly, but still unsure of M1.

Also the pot showed it only went to 420k on my multimeter.

 

[WTP Pepper]

1. 24V is way too high for an NE555 to operate.
2. What is R4 used for?

 

[syntax_x]

I could attack the 5v feed to the relay instead.