[Solved] 1 switch to control 2 power sources

I have 4 AA batteries powering an LED array and a 9V powering my Arduino and a radio receiver.

I would like to have just 1 on/off switch to turn on both power sources but since each have a separate circuit, I can't come up with a way to do it. Is this possible and if so, how would I wire it up?

A double pole switch?

(two switches in one)

I dont think so. I want if the switch is on then both circuits are on and if the switch is off, then both are off. Never a 1 on 1 off situation.

What if I used a transistor so that if I turned the switch on, it would turn on the 9V which would have a lead to the transistor to start powering the 4 AA batteries?

Use a On/Off DPDT switch:

A double pole, single throw is what is needed.

Of course a double pole double throw would work, but half of your switch would be unused. May be easier to locate tho.

shiznatix: I dont think so. I want if the switch is on then both circuits are on and if the switch is off, then both are off. Never a 1 on 1 off situation.

That's exactly what a double pole switch does.

Sometime a picture is worth a thousand words.

Ahha, ok, I understand now.

But, theoretically, could a transistor work for this? Have 2 separate grounds and Vcc lines with the switch powering the 9V which is connected to the base of the transistor and completes the circuit of the 4 AA's? I am just asking because these are things that I could get today but getting the proper power switch and settings everything to a common ground would take me much more time. Are there any reasons one would be better than the other?

shiznatix: Ahha, ok, I understand now.

But, theoretically, could a transistor work for this? Have 2 separate grounds and Vcc lines with the switch powering the 9V which is connected to the base of the transistor and completes the circuit of the 4 AA's?

Sure, but: a) The 9V and 5V grounds have to be tied together. b) The transistor goes after the LED array, ie. transistor's emitter is connected to ground (assuming an NPN transistor). c) Add a pull-down resistor to the transistor base.

Or maybe do it the other way around, ie. make the 5V turn on the 9V.

It doesn't matter to me which turns on the other, it is just that i did a bunch of assembly without thinking properly about the on/off switch and made both circuits separate.

So, I am looking for a way to do it without making them a common ground and whatnot but would it really matter if I just physically connected the 2 ground lines?

Also, what would be the difference if I made the 5V turn on the 9V with a transistor?

I don't understand yet. Do you want them to have a common ground or not? Are the two circuits connected together, or completely separate?

You don't have a switch laying around, or a store close to you?

I think for what you have said so far, the switch will be much better.

I don't want them to have a common ground, no.

I have a switch here but I tried to use the transistor and had odd results (could get some current to the test LED but only when I held the 9V battery - I think I might have wired it incorrectly?).

Stores are a pain here. Very painful.

The switch could be gotten but I still would prefer a non-common ground.

Using the switch, you do not need a common ground. The switch has 2 contacts. Just hook one between the 9 volt supply, and the 9 volt load. hook the other between the 5 volt supply, and the 5 volt load. Keep the grounds just hooked to each load, not common.

shiznatix: but would it really matter if I just physically connected the 2 ground lines?

No.

In fact, if the Arduino is connected to the LEDs in any way then you MUST have a common ground (it's not optional).

I can't be sure, but I think the two are not connected together, from his statement

I would like to have just 1 on/off switch to turn on both power sources but since each have a separate circuit....

If they are connected together, that would be different. Are they, or are they not ?

Ok maybe I am not understanding my own circuit. I have 2 batteries, 1 that runs the Vcc and Gnd for the shift registers, which power the LED array, and another set of +- that power a radio receiver.

Now, when I wire them up everything works perfectly. LEDs are bright, radio receiver works etc.

If though, I remove the battery that powers the registers and LEDs, I still get the LEDs working but just much, much dimmer. Could this be a solder problem or do the registers actually do the linking?

If I try to ground the 1 battery to the other, it kills the LEDs until I put it back to disconnected or grounded to its own battery pack.

When trying a transistor, it works well with the switch but when I use a multimeter, I still get a current from the collector to the emitter, regardless of the "control" circuit. This means that the battery is draining, yes?

What am I doing wrong here?

You said

I don't want them to have a common ground, no.

Did you provide a schematic of the devices and I missed, or no schematic yet? We need one now.

If the arduino and the led board are working together, then you will need a common ground.

Show us what you are doing. If nothing else, and you have a camera, draw it on paper and take a picture, and upload it. I anxiously await. Jack

I will try to draw my circuit tomorrow but I am not very professional.

The basic text version is that I have 2 power and ground lines that are separate in the soldering (all totally separated and soldered in their own "bars"). When I connect my registers, I put them on the 5v (4 AA battery) ground and power line. When I connect my radio receiver, I put them on the 5v and ground from the Arduino. I have a 9v attached to 1 of the Gnd lines on my Arduino Micro and the + part of the 9v connected to the Vin of the Ardino.

If I disconnect the 4 AA batteries, I still get the LEDs lighting but they have very dim lighting. What I am guessing is that the clock, register, in, or whatever pin is finalizing the circuit when the other battery is not attached and causing problems. Maybe I have a bad connection somewhere?

Anyway, if it is still not clear I willl have a circuit design within a day

Ok, attached is a basic idea of my circuit. Like I said, If I detach the AA batteries, it still works but is very dim. I am using push registers to power the columns and sink registers to turn each row on/off.

What can I do to have a 1 switch on/off for everything?

simple-sketch.png

Ok, in your schematic, we see that your arduino is sending signals to the shift registers, so you will need a common ground.

When you send a signal from one board to another, you need a common ground so the signal can be detected on the receiving board.