I'm not sure how to determine current drain. Its a small dc motor (fish feeder) that runs on two AA batteries. Basically I'll be bypassing the circuit board and going straight to the motor(not sure if I need anything between the motor and the power supply??). From there my aquacontroller will turn it on and off once a day.

 

I have a 5 volt DC wall adapter ...

If it's already regulated at 5v (is it a USB charger, for instance?), you could certainly get by with a couple diodes to drop the voltage. They just need to be rated for 2X or more current than your device needs. If it's a standard old wall wart, the true voltage could be 6V or more and rippling. A voltage regulator might be appropriate.

As noted, the answers depend on your load device.

[update] Ah, I see it's a small motor. This won't care about a small ripple or even a fairly large voltage fluctuation, as long as you stay below its rated voltage.

 

It's a power supply from a small ethernet switch.

 

Do you have a multimeter? You could measure the power supply voltage and also the current used by the motor. (Be sure to measure current in SERIES, don't just put the leads across the motor terminals or you'll need a new fuse for your meter.)

You could even get by with just a resistor in series with the motor, if you know those two measurements.

 

I do have a multimeter, but I can say that I have never measured current. The meter is from my HVAC days so I know it's a good meter.

Basically I just want to make sure I don't burn out the motor. The simplest solution is what I'm looking for right now.

 

...but I can say that I have never measured current...

It's easy, just take a moment to learn how to use your meter for this. You may need to put the leads onto a different terminal on your meter. And again, no matter what, don't put the leads in parallel to the load. Classic newb mistake.

Your motor probably draws 100mA±5X (20-500mA).

 

Ok so here is where I need help now. I have the 5-3.2 volt converter made, it works great! So the unit I'm powering has a small switch built into it. The switch is powered all the time, when a button is pressed, the switch opens (cutting power from it) and the motor makes the drive turn one full rotation and when the switch closes, the motor stops. Now, here's the scenario I'm trying to achieve. The controller I'm using for this aquarium has a bank of outlets and the controller turns the outlets on and off as per my programming. Right now, I have it set to just provide power to the motor for 8 seconds, but over time the rotation gets out of sync. So is there a way I can use the controller, power turning on and off, and still use the switch so the unit makes one full turn utilizing the internal switch?

 

This wasn't clear (to me, anyway). Can you sketch out a diagram? I think I understand what you want - one and only one complete feeding cycle each time power is applied. I just don't quite get the existing arrangement of switches.

 

First off, thank you again for all your help with my random aquatic projects. I'm back to my original project, which now seems to be working with the temp sensor. My latest question is, does this circuit support PWM fans? If not, is it hard to make it PWM compatible?
Also, if you have picaxe programming knowledge, please help me figure out what the min and max temps set in this program are. I assume they are Celsius but I can't be sure.

Here is a link to the circuit and programming code.
http://ozreef.org/content/view/297/29/

 

That circuit will support PWM speed control of a DC "brushed" motor fan...but not a BLDC (BrushLessDC) motor fan.
It will support ON-OFF control of either type of DC fan.
Ken