Posted by Druin on 10, 2000 at 10:14 AM:
In Reply to: multiple buttons into one. Possible?? posted by Michael C. on 10, 2000 at 8:33 AM:
For triggering multiple switches with one, it all depends on the nature of the buttons you're trying to combine into one.
For your thought on wiring 3 wires together and having the one switch for it, that would work *IF* the 3 switches work on a "common ground" type system, where the ground could be either the - or + supply rail.
For instance, a keyboard encoder in direct mode. If you were wiring the 3 switches normally to a keyboard encoder with direct mode (common ground), then all the 3 switches are activated separately by connecting the first contact wire to ground, the second contact wire.
So what happens when you have your 3 separate switches like this and you press 2 of them at the same time? You're routing two keyboard inputs to ground, and so what you really have is the two switch wires connected to each other too. They run down to ground, along ground, and into each other while both are pressed. The key is that they are indeed connected to ground, but also to each other in the process. Hence you can wire them to the one switch by having your common ground on one contact of the single switch, and then run the other wire of each input to the other single switch terminal, then you'll ground all 3 switches at once with the press.
Supposing you have a keyboard encoder in matrix mode, or some other type of system that the switches belong to. Then each particular switch has 2 distinct wire paths, and by trying to wire them all to one switch directly, you have 2 or 3 rows/colums all shorted permanently together on one single switch contact, and another possible 2 or 3 columns/rows shorted permanently together on the other single switch contact you're trying to use, and it will be chaos.
But there is hope.
Look into "Analog Switch IC's" such as the 4066, 4053, and others. If you go to a chip manufacturer's site such as www.fairchildsemi.com and do a search for "4066" or "4053" and pull up the data sheet PDF files, you'll see what they can do.
I used the 4066 in my Rotary Interface, where I did have separate controls for each switch, but I could have easily wired the controls together and turned on all 4 output switches with just one single "switch" input.
What these chips do is they pass a signal through 2 wires (ie a switch) when the control wire is high. When the control wire is low, the signal at the chip inputs is inhibited (switch is unpressed)...
So you take your 3 switches you want to combine, and you run their wires to switch inputs on the chips. That way you still have 3 distinct circuit paths, no wires are connected together and whatever type of keyboard encoder or other joystick thing you're tapping the switches from, will still behave as it was designed.
Now you have 3 isolated switch circuits wired to the chip, and instead of pressing switches, you want to apply +5 volts or Ground to press/release. NOW you can wire THOSE control signals together! You have a single control wire for switch 1, another for switch 2, and another for switch 3. You run those all together to one real switch contact, and also from this real switch terminal, connect a 10k resistor to ground. The other switch contact will be wired to +5v.
THe resistor will hold the 3 switch control lines low when nothing else is happening, so the chip will act like a switch that's not pressed. When you press your one real switch, you override the resistor and the 3 control lines route directly to +5v, a high signal, and the chip will turn on all 3 switches at once.
I don't know how much help any of this was, but I'll draw a schematic and link it here to illustrate that chip method.