Pololu Switch Questions

I am making a project where I want to have the user turn it on by pressing a momentary PB and the controller will power itself off programmatically.

I am using an Arduino Duemilanove and the Pololu Power Switch (item #750) and it will be powered by a battery pack.

I have several questions about how to wire it up.

1: In another thread (Pushbutton Power Switch Questions) it was mentioned that in order to have it so the PB can only turn the arduino ON, the PB should be connected to the Ground on one of its contacts and the PB should be connected “to the switch pad that is closest to the edge of the board” on the Pololu switch. Is this the way I need to wire the PB to the switch?

Does this mean that if I wire the PB to the two contacts where the little PB that comes with the unit are plugged in then the PB will act in an alternating power on/power off manner?

2: I have read the description of the Arduino’s external power connector, 5V and Vin connectors but am still confused. I think that I should wire the battery pack’s positive lead to the Pololu switch’s Vin and the Battery’s negative to the Pololu switch ground. I don’t know what to connect the Pololu switch’s VOut to. Should I connect it to the Arduino’s external power connector? to the Arduino’s Vin? or to the Arduino’s 5V pin?

3: Do I need to tie the Pololu switch’s two Vin points to each other and the two Vout points ot each other and the four Ground points to each other?


  1. It would be nice if you provided a link to the thread. It sounds like your question amounts to, “am I supposed to wire the switch the way you said to wire the switch?” The answer to that is yes, obviously, but I suspect there is some distinction you are making that I do not understand. The default operation is indeed the power on/off alternation.

  2. You definitely have to go from the battery to the switch, and from the switch to the Arduino. The general point is that when the switch is on, you should be able to think of it as just a wire, and you need to connect power to wherever you would if the switch were not in the circuit. The power connector sure sounds like place to connect. Did you look at the schematic of the Arduino? It looks like the only difference between the power connector and VIN is a reverse protection diode. 5V is absolutely not the place to connect raw battery power; that would just be asking for destroying your Arduino.

  3. No, they are already connected on the board. The idea is that there are extra pins there to handle extra current; for just an Arduino, you can just use one pin for each connection (so a total of four wires to the switch: two from the battery, two to the Arduino).

- Jan

Thanks for the quick response.

1: The thread I referred to was Pushbutton Power Switch question
Circuit theory has always been a weakness to me. It never occurred to me that a switch could be alternating states but by connecting the Pushbutton differently the switch would work one way only. That is why I asked specifically about the other thread’s answer.

2: I had read the description from the Arduino site of the three power connection points for the Arduino at least thirty times and could never get to the point where I felt comfortable that I understood the differences between the three and which one I should use. That is why I asked the question.

When I got your answer I downloaded the Arduino schematic and because of my weak understanding of circuits that didn’t give me any comfort in understanding the situation any better. Your response did answer all my doubts though.

The project I am building is the Reverse Geocache described on the Arduiniana site. Since it just describes in broad brushes the concepts, I have been learning as I proceeded. I ended up ordering parts from 4 places and because each time I received an order I found I needed “one more part”, I placed as many as four orders from some sites for parts.

This has been a complete learning experience for me and I thank you for your help.

So, you’re all set now, or are you still not clear on question 1?

By the way, that switch product is a particular circuit that happens to work that way, plus the feature you want is actually less than what it is meant to do. In general, circuits do different things if you change them, and being able to get something less complicated than the original function should not be too surprising. We do not show the circuit on the web site, so you should not expect to have been able to figure out that this different wiring of the switch would produce your desired behavior.

- Jan

I’m clear on all my questions now. Thanks for your help.

I assume that the person who designed the original Reverse Geocache chose the switch for its ability to be able to have the Arduino code turn it off. I’m just using the parts he mentioned and figuring out how to make them work together to get the desired outcome.

Hi, I recently bought the SV version on the switch. Today I wired up the circuit to provide power to a microcontroller (Arduino Uno, to be exact), which runs a servo, GPS and LCD. I’ve got 9v going in, a momentary NO switch connected, and voltage going out to a barrel connector for the Uno. However, I am having trouble. When I click the switch, power comes on, but it arrives jerkingly, on off, on off, on off, sometimes stabilizes sometimes doesn’t. I’ve also noticed that pushing the switch again turns the circuit off (though I’m positive this is a momentary switch, the same performance occurs with the provided switch as well). Any ideas what might be going on?

Thanks in advance.

Hi. Does the switch work properly without the Arduino connected?

- Jan

Actually, I think I identified the problem.

A 9v dry cell went in to the switch, if I turn it on it seems I get about 7.25V at the barrel. When I plug it in to the board with no peripherals attached, the board powers, but I can see the lights on the board dimming intermittently. If I check the voltage out at the 5v pin it reads around 3.5 or less (fluctuates a little). If I check the vin pin, which is supposed to be power, then I get 4.5v.

I decided to try and check what happens when I get direct 9V battery power. Everything is fine. I decided to then try this with the SAME BATTERY as with the switch and presto, same problem. So, it seems the issue was a cheap battery I was sent along with a separate kit.

Thanks for your help!