I've got a program running on the Arduino that is supposed to turn on and off a pump. currently, I am outputting the reads of the components that need to be read and it shows when the port (port 13) is supposed to turn on and when it's supposed to turn off. When I use a multimeter between the port 13 and ground, everything works as expected.

When I start the program and the port is off, I get a reading of 0.03v @20v max (to be more precise, I get 14.0 at 200mV) - Shouldn't this be zero? or is there always going to be some electricity flowing?

When the port is turned on: digitalWrite(airPump, HIGH); (and yes, airPump is set to 13), the voltage reads between 4.0 and 4.51 with spikes down to 3.65 on my multimeter set at 20v max. is it ever stable? (pictured below) enter image description here

So, the main question is: I'm supposed to be sending the power from port 13 to a DC-DC converter. I tested the converter on a separate bread board just by itself. I used a DC power supply and set it to 4.5v, then ran the power through the vIn, grounded the ground pin and ran the vOut to the multimeter (then to ground with the multimeter) and I got it set to output only 2.5v with a constant 4.5 running into it. (pictured below) enter image description here

I also tested whether or not changing the voltage input would change the output at all and it seems it does not, from 1.5-15v, the converter stays steady at 2.5v

Now when I do the exact same set up on the arduino with the power from port 13 running into the voltage in on the DC-DC converter, it gives me a reading of 0.01v. Any idea why this is happening? enter image description here

I've checked probably over 30 times and rearranged everything just as many, but nothing seems to help. I can't get a stable 2.5V output from the converter with the arduino...

UPDATE: Below is a simple wiring diagram: enter image description here

The image shows what it is supposed to do, but for testing purposes I made it so if the rH is higher than average (I just breath on it) then the pump will turn on.

  • Are you connecting the output pin of the Arduino directly to the input of the DC-DC converter? A circuit diagram will help.
    – Craig
    May 13 '14 at 17:13
  • I am (through a breadboard) The output pin 13 goes directly to the DC-DC converter voltage in. Is there a good, free place to do diagrams with components like these?
    – ntgCleaner
    May 13 '14 at 17:27
  • @Craig Diagram updated.
    – ntgCleaner
    May 13 '14 at 18:38

The arduino output pin cannot provide enough current to drive the pump. The DC-DC converter is not designed for this use.

You need external power supply with enough current to drive the motor that you switch on and off with the arduino output pin.

Search for "Arduino 3V DC motor control" for examples of how to do this, there are many options.

  • Or use a high-side load switch. May 13 '14 at 20:24
  • Hmm, That's strange, when I read the multimeter it shows it's driving enough voltage, though not consistent. So I will need to use the arduino just to turn a switch on from a power supply to the pump? I will look into this. Thank you - I will also look into a high-side load switch.
    – ntgCleaner
    May 13 '14 at 20:35

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