In powering my arduino I have been using 4 NiMH which produce approximately 5.2V which I connect to the 5V pin. That battery pack doesn’t produce enough voltage to insert a regulator and still have 5V. Since the battery pack will always produce 5.2V or less, do you think there is an actual need for regulation? I would like to stay with this battery pack because it is the ideal size for my application.
It is generally not great practice to power an Arduino through its 5V pin, especially with an unregulated voltage. If you decide to go this route, you will need to be careful to never power your Arduino though its 5V pin at the same time as any of the other power inputs (including USB, the barrel jack connector, and the VIN pin) since doing so would likely result in two different voltages being shorted together.
I am not sure what Arduino you have, but the absolute maximum logic voltage on many Arduinos is 5.5V, which four fully-charged NiMH batteries can exceed (they will usually be close to 6V). It is safer to use a regulated voltage to power the microcontroller, and this also has some other advantages such as providing a more stable analog reference voltage. You could use an appropriate step-up/step-down regulator to get 5V from your batteries, but given the concerns I raised previously about powering an Arduino through its 5V pin, you might instead consider using a step-up regulator that will allow you to power your Arduino comfortably through VIN (at least 7V for an Uno).
Alternatively, you might consider using one of our A-Stars instead of an Arduino. The A-Stars are Arduino compatible microcontrollers which, among other improvements, use regulators that allow them to operate with a wider range of VIN voltages than normal Arduinos. For example, you could comfortably power the A-Star 32U4 Prime LV through VIN directly from your battery pack.
Thanks, Patrick. Your insight is always right on target. Now I’m thinking that as much as I like the 4 D-cell battery pack, I might adding 2 more NiMH. Six cells ought to kick the voltage up to around 8V (with NiMH batteries). That should let me power the Vin pin, which is already regulated if I understand correctly. That should also give my stepper motor a little longer run-time, which has always been a concern. For the record, I’ve been testing stuff with an Arduino Uno v3, but will soon switch to a Nano, only for the space saving. The A-Star sounds interesting, but I already have the Arduinos and would like to not waste them.