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Q*bert Knocker
In this section...
Pinball Plunger Circuit Overview
The programmers of Visual Pinball and PinMAME have made it possible to
emulate/simulate pinball games on the PC. This section includes the design
specifications of the Pinball Plunger Circuit that I designed for use in my
Retro Arcade cabinet.
I wanted to create the most realistic pinball experience possible on my cabinet
by using an actual pinball plunger to launch the ball on-screen.
I chose to use a reflective opto-switch to sense the presence of the plunger's
home position and a debounce circuit to remove any bouncing effects from the
plunger. Without a debounce, the bounce of the plunger after release would behave
like hitting the assigned plunger key in Visual Pinball repeatedly.
Mount the reflective opto-switch close to the end of the plunger. Doing so will
provide the most realistic feel from small shots with minimal pull of the plunger
all the way to hard shots with maximum pull. I'm not doing anything super special or magical. As soon as the opto beam is broken, it is like holding the <enter> key in VP. It just so happens that pulling the plunger all the way out and releasing is equal to a maximum strength hit and a very short pull and release is like a minimum strength hit in VP. This is the only possible way to utilize a plunger with VP.
My design uses +5 volts from the computer's power supply to power the circuit.
The debounce components consist of U1, C1, and R1. The input of the debounce circuit
comes from the reflective opto-switch. This signal is cleaned by the debounce
circuit and then sent to the I-PAC encoder board.
Changing the position of JP1 allows you to select between negative or positive
encoders. Check with your encoder's documentation to find out what jumper
position you need. Use position 2-3 for negative (0V) output or position 1-2 for
positive (+5V). I-PAC uses the first option. I am also using resistors R3 and R4
soldered directly into the wiring harness of the reflective opto-switch to
simplify the PCB design and reduce connector inputs.
The reflective opto-switch I used was very susceptible to ambient light. Keep
that in mind when you test the circuit before you close it up in your control
panel. R2 and LED1 are only for testing the circuit and are not required. I still
recommend it so that you don't have to fuss with holding your voltmeter and
moving the plunger at the same time for testing.
The reflective opto-switch I used in this project has been discontinued by
Sharp. I used it because I had one lying around. You will have success with just
about any reflective opto-switch you find. It looks like the very popular
Fairchild QRB1134 should be a direct replacement.
Pinball Plunger Circuit Parts List
| IC1 |
74LS14N (Mouser P/N# 512-DM74LS14N) |
| R1 |
1K Ohm ¼ Watt Resistor (Radio Shack) |
| R2 |
220 Ohm ¼ Watt Resistor (Radio Shack) |
| C1 |
10 uF Electrolytic Capacitor (anything above 10v)( Radio Shack) (Check polarity!) |
| LED1 |
Green LED (Radio Shack) |
| SL1 |
Computer Disk Drive Power Connector(Mouser P/N# 538-15-24-4345) |
| JP1 |
3 Position Jumper (Mouser P/N# 544-CA-S36SP100 and 151-8000 jumper) |
| X1 |
4 Position Phoenix Connector(Mouser P/N# 651-1729144) |
| Opto-switch |
Sharp GP2L24 Reflective Opto-switch |
| R3 |
Resistor in harness - 300 Ohm ¼ Watt Resistor |
| R4 |
Resistor in harness - 10K Ohm ¼ Watt Resistor |
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