Main > Main Forum
Need help with T2 solenoid driver circuit!
(1/9) > >>
1UP:
OK, I'm finally going to get my Terminator 2 guns up and running.  As we know, the T2 gun has a solenoid or pinball coil driving a metal piston which causes a recoil feedback when firing the gun.

I'm trying to build a circuit from scratch which will interface the Ipac LED harness to drive the 24V power supply I've connected to the solenoid.  Dave Widel already has a software hack that sends the recoil and LED signals from the game to the CAPS/NUM/Scroll Lock LEDs on the keyboard (or Ipac LED harness).

The hardware part is done by using the recoil signal (5v) to switch a high-voltage power transistor, thus turning on and off the 24v power supply to the coil.



So far, the circuit has only been tested by driving a brighter LED, (since I don't want to risk frying my Ipac with 24V until I know what I'm doing) but it seems to work!  The question is, if my transistor can take a 5V, 2A current at the base, do I need any kind of resistor to protect the transistor from the Ipac current (5V @ 10ma) or vice versa?  Are there any problems with my circuit that strike you?  Any other suggestions?

Thanks
Ron Michallick:
::)

The only reason the LED lights is the R1 to transistor
base-emitter diode. There is no gain and the caps are
blocking not filtering the recified AC. With luck the caps
may not explode, but it'll never drive the coil.

Doom and gloom aside, send me an email and I'll send
you an alternate circuit.

Ron.
ErikRuud:
Whatever circuit you use, make sure you protect against "Back EMF".

A solenoid is an electro magnetic coil.  When you put power through it, you get a magnetic field.  When you turn the power off, the magnetic field collapses.  The collapsing magneic field passes through the wire in the solenoid, it actually generates a small amount of current.  The polarity of this current is reversed.  So you get a small pulse of power running backwards through your circuit.  This could harm your IPac.

You need to isloate the coil from the IPac.  One way is to use a small diode to block the reverse flow.

Carsten Carlos:
Yep, don't forget the diode mentioned before - but not TO small ;)
If you have to use a 24V-power anyway, why not use a relay (don't know if there are any 10mA relays out there, but electronics get better, so why not?)?
So you don't even need to hook up the 24V-ground with your PC-ground!
ErikRuud:
Yes, a relay wood be good.  You can eve get solid state ones that do not click.  That way you would isolate the 24 volts from your IPac, and your motherboard.

However, a regular relay is also an electromagnetic device, so yo will still need a diode to block the back EMF.

As a side note, we actually make use of back EMF in slot car racing to create dynamic braking when we release the trigger on the controllers.
Navigation
Message Index
Next page

Go to full version