Simple Credit-add mod

[electronrancher]

Hey all,

I have worked out a simple credit-add circuit in 100% ANALOG circuitry. It uses 15 transistors, 18 resistors, one cap, and a pushbutton. I'm wondering whether there is any interest in this sort of thing - you whack the button and one credit is added. For 50 credits, you whack the button 50 times. It may be useful for those who don't have an eprom burner, etc, but do have access to radio-shack style parts.

Feedback?

[azlew]

Thanks for doing all that work on a credit add mod.

You asked for input and I would prefer myself to have a mod where you just hit it and it gives a credit of 50.

[rupan777]

Sounds intriguing Can you post schems or are you planning to make something from it?

[Sid]

Sounds interesting...

[MrGneiss]

Sounds interesting...

I concur.

[Sid]

Now if we could only get someone to design a mod that with a push of a button will leave a comment for me in the contest thread....

[musky]

I'd like to see it, sounds interesting

[electronrancher]

ok - give me a day to finish it up (I've been too busy to build it up, but it works in sim so I think it's solid) and I will post the schematics here.
cheers!
-er

[electronrancher]

Ahh, the beauty of analog. Although I don't show it, you should put a cap between +5v and ground (the power supply), as always.

OUT1 and OUT2 go to sensor 1 and sensor 2, respectively. The outputs are active low, meaning they pull down the sensor lines - this is the most common way to do it. They should be able to pull down anything up to about 30v, so even 24v machines should be fine.

Here's how it works - when the pushbutton is pressed, it clears the cap and inhibits the circuit from giving output via Q9-Q11. When the pushbutton is released, the charging of the cap is sensed at 4 levels via Q1-Q4, and the outputs are gated together to create the familiar "two overlapping pulses" that represent a token.

All the pnp's are 2n3906 or equivalent, all the npn's are 2n3904 or equivalent.

Leave your feedback here, I will try to help debug if anyone has issues.

First page is the schematic, second page is the sim trace if you want some simple debugging info. I suggest replacing the cap with a potentiometer if you're having trouble, then you can sweep the voltage at Q1's base from 0 to 5v, making sure all the levels trigger where they're supposed to.

Threshold 1: Vcap=650mV, OUT1 goes low
Threshold 2: Vcap=1.75V, OUT2 goes low
Threshold 3: Vcap=2v, OUT1 goes high
Threshold 4: Vcap=2.25v, OUT2 goes high

If you need to power the circuit from 12v, you'll need a bigger cap. Other than that, everything should work out, mathematics wise, to keep the timings relative.

[electronrancher]

nope i'm sorry i'm an idiot - the thresholds are generated relative to Vcc, so everything washes out and you do NOT need a cap change for a change in Vcc. heh - last minute change, i forgot!

[logicprobe]

Cool...
Any live testing, or just sim at this point?

[electronrancher]

no i built one up, it works fine. the schematics here are actually rev 2, i found a problem when i built it that needed a little tuneup.