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Gun Solenoid Timing

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Ropi Jo:
Hoping some electronic minded bods can offer a little help here.

I've just about finished my scratch built positional gun for my modular mame cab. It's very basic and well below arcade quality but it suits my needs.... and it cost ZERO!

I've used a relay oscillator circuit to control the machine gun speed (if I knew more about computers I would have tried to use mamehooker, but that option will have to wait for another day)

Had to overcome loads of problems during the build and now just one issue remains.... I could really do with lowering the duty cycle.

The DC is currently around 50-60%, firing the solenoid at about 10hz.

Can anybody suggest a circuit / mod that will accomplish this? I'm getting too old and my old brain is struggling with this.

I'm using the NO contacts on the other side of the relay to input a transistor circuit with 5V which then switches the solenoid through a darlington.... not shown.

EDIT TO ADD....forgot I have dropped the supply V down to 14V. This slowed the pull-in of the relay. At 24V the duty cycle was closer to 80%. I can't go any lower as it's a 24V relay and it won't operate any lower than 14V.

Thanks





PL1:

--- Quote from: Ropi Jo on January 18, 2021, 03:25:43 pm ---I could really do with lowering the duty cycle.

The DC is currently around 50-60%, firing the solenoid at about 10hz.

Can anybody suggest a circuit / mod that will accomplish this?

--- End quote ---
Been a long time since I've messed with them, but have you looked into using a 555 timer circuit?
- You can change component values to adjust the frequency and/or duty cycle.

Examples:
https://www.multisim.com/content/tf7Mwpy2CctfFaaVEr4SeN/555-variable-duty-cycle-constant-frequency-astable-multivibrator/

https://www.quora.com/How-can-I-vary-duty-cycle-of-an-astable-Multivibrator?share=1

https://www.electroschematics.com/pulse-generator-with-555/

https://www.electronicshub.org/astable-multivibrator-using-555-timer/

Component calculators:
https://www.rfwireless-world.com/calculators/Astable-Multivibrator-frequency-and-duty-cycle-calculator.html

https://www.daycounter.com/Calculators/NE555-Calculator.phtml


Scott

Ropi Jo:
Hey Scott,

I did find 2 old 555s in the junk box and pulled a circuit from the internet (not any of the above).

Somehow I managed to blow up both while trying R and C values to get what I was after.

Went back to the relay method and just worked with that.

I tried to use the spare N/O contacts to drive the solenoid directly but the arcing meant the contacts wouldn't last too long. The solenoid draws a big pull-in current. And the spikes were crashing the apac.

Once I got the transister output working and suppressed all contacts the apac was happy.

I actually cheated on the transister circuit as I found a board in the junk that originally drove 4 solenoids, and had on board emf suppression so I hacked into that.

It's currently 'just right', other than the solenoid getting a little hotter than I'm comfortable with, hence the DC.

I seem to remember there was a simple RC network you could add accross a square wave to modify it's pattern but blown if I can remenber what it was called.

Oh to be 16 again!

Ropi Jo:
BINGO.... I think.



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