Monostable Multivibrator Output

My device is powered by the USB supply but it exposes a 5v terminal. I was planning to power the one-shot's using that.

I have taken some readings with my multimeter. By connecting the positive lead to one of the device inputs and the negative lead to the ground I see 0.75v and 0.07mA.

The input connection through the meter isn't registering as switch closure on the device. If I connect the input to ground with a wire the device sees the switch closed but I can't measure any voltage or current between the input and ground.

What is the correct way to measure this? Sorry for my ignorance.

That _is_ the correct way for static inputs, and I'm surprised the ammeter didn't show up as a closed switch. Looking at the thing on their web site:

however, makes me think the inputs are scanned. That could be the reason for the low voltage and, I suppose, if your meter has enough inductance in the current measuring circuitry that could keep the chip from reading a ground.

They can be contacted via email, so that might be the best way to find out the maximum resistance the thing can see and still think a closed switch is out there.

Then there's always rec.games.video.arcade.collecting...

How did you know it was the A-PAC? You got it right.

Taking into consideration I was measuring correctly and that the A-PAC input may be scanned, am I correct in thinking there isn't a problem with the one-shot handling an input with the measurements I got?

Conversely is it likely the 5v supplied one-shot output will be any issue with the lower voltage A-PAC inputs? Do I need to do something to protect the A-PAC input from the 5v one-shot output?

Will the one-shot itself provide any resistance that might keep the A-PAC from reading a ground? Does this possible sensitivity to resistance make the transistor option a better or worse choice?

Thank you for your expertise.

I really think this would serve you better. As I recall, you were using 4 toggle switches and wanted to have them act as if they were momentary switches, yet remain in the toggled position. You intend to add 555 monostables to get that effect. Here's a simpler solution.

C1 (4.7 uF) charges rapidly to Vcc (5V) when the toggle is off. When it is on, C1 discharges through R1 (10K), D1 and the game port controller until the voltage across it reduces to 4.3 volts. (The bottom of C1 rises from 0v to .7 volts). The game port "sees" only the change from 0V to .7 volts - the zener isolates it from C1 and D1 isolates it from Vcc.

If needed, you can change R1 to a pot for variable pulse width.

Ed

Your solution is beyond my current knowledge to understand, but I will put it together and see how it behaves.

My game port device has only terminal for each button input, which need to be connected to a common ground to activate. How is the connection to ground equivalent to the transition from 0v to .7v in your circuit?

I meant to day "My game port device has only one terminal for each button input".

Out of curiosity, why did you put the 10K resistor in the test circuit? I would have naively just done the following.

A-PAC ____ +-------+ +-------O O------|+5 | | S1 | | | | | | | | | C------|1R | | +--B | | | | E------|GND | | [1K] | | | | +-------+ +-----+

Thanks again for all the options. I have lots to play with now.

Thanks for the revised circuit Ed. I still don't understand how it makes the game port input behave as if it is grounded when switched on, but I am curious to try it. I might learn something in the process. :-)

I'm glad you asked - it made me look and I think that you might not need the Zener, D1 or R2 at all. I don't even remember what I was thinking when I put them in there. It was late at night, and I was beat, so chalk it up to that. I made a new diagram (see below) reflecting the changes, and also labeled the toggle.

My hope is that the experiment will work. It costs you only 2 cheap parts to try it. It is cheaper and smaller than the 555 circuit.

Answering your question: Your controller is a logic circuit, and logic circuits respond to .7 volts the same way they respond to 0 volts, or any voltage in between, so the fact that the capacitor voltage rises from 0 to .7 does not disturb the game port operation. But that's no longer relevant in the modified diagram.

Here's the modified diagram:

The toggle is shown in the off position, connecting a to b. In the on position, it connects a to c.

Ed

Think of it this way: with the regular momentary switch, you put a negative pulse into the game port - the pulse comes from the switch. With the toggle switch, you put a negative pulse into the game port - the pulse comes from the capacitor. The game port does not care where the pulse copmes from - it just "needs" to get a negative pulse.

Ed

John,

I just wanted to let you know tried your transistor circuit and it worked great to control the A-PAC. Now I just need to build the four button version I will install in my gutted RC radio. I am planning to use the edge-triggered quad KA558 to simplify things. Any opinions about that? Thanks again for everything.

-Kevin