Timer on/off delay

[Zool]

Hi All. This is my first time here. and can i just say thanks for having me.
i am a tinkerer in my spare time. I do IT for a living and am a big gamer and 3d printer.
I am designing pistol grips for my VR headset. and i am wanting to re-produce recoil on the gun grips.
i have a nice little spring loaded solinoid that gived a good feeling then supplied with an sharp on off of power.
But i would like a simple circuit so that then you press the button it supplies power to the servo for lets say .2 of a second. then cuts the power. even if you are still holding the button down.
Can anyone help with the smallest simplest design i could possably use? also my electronics knowledge is limited at best. but i can solder and i am not stupic

 

[AnalogKid]

Since it probably is safe to assume that the switch will be pressed for longer than 0.2 s every time, this is pretty simple. While a true monostable circuit will work, you don't need the input management provided by positive feedback. IOW, a simple pulse-former or "boxcar" circuit will work.

To do this, we need to know the voltage available to drive the solenoid. and the solenoid resistance.

Also, what is the minimum time between successive switch presses? If it is very short, the circuit will need a little extra to reset the timing capacitor each cycle.

And something that could make things very simple - is the switch SPST or SPDT? Even better - Manufacturer and part number for the switch, plus a photo showing the terminals.

ak

 

[aliarifat794]

You can use a microcontroller or 555 for this task.

 

[AnalogKid]

Or (depending on the switch answers), one capacitor.

 

[Zool]

Ok. Guys. Great replies and thank you. When I said I'm not stupid... I'm a little bit more stupid than that haha. I'm not fully following but I'll show you what I have at hand. But if you can suggest better as long as it won't break the bank I'm all ears. The micro switch with long leaver will sit over the trigger of the controller. And I thought powering with a 9v battery and resistor to bring it down to 6v for the solenoid? As for how quickly it will be pressed. It could be pretty quickly. It's for shooting games so if you imagine firing off quite rapidly. Alternatively if this complicates things I could just make it so that it just turns the solenoid on and off and skip anything fancy?

 

[AnalogKid]

1.5 A is a lot to expect from a 9 V battery, even in short pulses. OTOH, because the pulses are so short, you probably can connect the battery directly to the solenoid without fear of the solenoid overheating.

The switch has three terminals, which is excellent. The most simple approach also is impractical - one 50,000 uF, 10 V capacitor. The cap is connected to the battery when the switch is relaxed, and connected to the solenoid when the switch is pressed. You could add in a 2 ohm resistor for rapid recharging of the cap, but the battery's ESR (Equivalent Series Resistance) probably is high enough to protect the switch contacts.

The next layer is an R-C timing circuit with a transistor. Same basic concept as with the large cap, but now a much smaller cap drives the base or gate of a small power transistor, turning it on for 0.2 s. The pulse to the solenoid would be an exponential spike - very rapid turn on for a good recoil punch on press, and a slower turn off for much less recoil on release.

With a small power MOSFET, the cap can be something like 10 uF. This approach could be both smaller and cheaper than the single large cap.

What types of electronic components do you have access to?

ak

 

[Zool]

I'm in the UK. But I can order anything I would need. If you would have the time to give me a shopping list and a schematic (remembering I'm a muggle) I can order anything I need. I do have a kit here that my kids got and never used. Attaching pic in case there is anything in there I could use

 

[AnalogKid]

Kit picture - ?

Here is a first pass at a schematic. The parts are what is in my design libraries, not strict recommendations.

Q1 - n-channel power MOSFET rated for at least 10 V and 5 A
C1 - 10 uF capacitor, rated for at least 20 V
R1 - 10 K resistor, any wattage or tolerance
D1 - 1N4001 - 1N4004

SW1 pin 1 is the normally-closed (NC) contact. Pin 3 is the normally-open (NO) contact.

When the switch is relaxed, B1 charges up C1 and the circuit sits.

When SW1 is pressed, the charge in C1 is dumped onto the FET gate, pushing it to full enhancement ("saturation") rapidly. The voltage at the gate begins to decrease exponentially as R1 discharges C1. After two time constants (2 x R x C), the gate voltage is low enough for Q1 to begin to turn off and release the solenoid.

When SW1 is released, B1 immediately recharges C1 for another cycle.

Note that there is no power drain (except for C1 and Q1 leakage currents, a few microamps) when the circuit is idle.

ak

 

[Zool]

Amazing. Ok. I will order these up tomorrow. And update on progress. Thank you so much for taking the time to do that for me. I really appreciate it. It's so frustrating when you have an idea in your head but don't know quite how to carry it out.

 

[AnalogKid]

I will order these up tomorrow.

Hopefully not the part numbers in the schematic. The 31N50 is massive overkill, and surface mount.

ak

 

[Tony Stewart]

Before you order parts , you better decide on the voltage regulator. The 9V alkaline has about 0.5 Ah or 1800 As when used gently but derated when dumped with 1A spikes. You might only get a few hours of game play.

You might want to get a bunch of 1 uF caps to start with a faster recoil and add as required as 200 ms seems a tad long. Then use a regulator to drop 3 or 4 volts.

 

[Zool]

I was messing with the solenoid last night and at 6v it hardly pulls. But at straight 9v it's got a nice pull to it. And in short bursts like shooting it does not really heat up. So I am thinking not to drop the voltage now.

 

[Tony Stewart]

I was messing with the solenoid last night and at 6v it hardly pulls. But at straight 9v it's got a nice pull to it. And in short bursts like shooting it does not really heat up. So I am thinking not to drop the voltage now.

Fair enough, but how many shots do you expect from this battery?

 

[ZipZapOuch]

If you use standard 9v alkaline, you may overheat it if you are rapid firing for hours of game play. If you use an Energizer 9v "ultimate lithium" battery (disposable/non-rechargable), those are made for 1.5A pulse or up to 1A continuous use. A bit pricier but the right battery for your application.

 

[Zool]

If you use standard 9v alkaline, you may overheat it if you are rapid firing for hours of game play. If you use an Energizer 9v "ultimate lithium" battery (disposable/non-rechargable), those are made for 1.5A pulse or up to 1A continuous use. A bit pricier but the right battery for your application.

I may try this battery. I have actually found that this set up in testing is a bit weak. I'll give this battery a go see if there is any difference. But I might be going back to the drawing board