I just told you everything I know about stepper motors.
I'm working on a device that will provide a visual indicator that the postman has delivered mail to a multi-box installation at the head of a cul-de-sac. One solution would involve turning a very light weight piece of plastic so as to expose its orange part. Then in the middle of the night it would be moved back to the original position. The positions are bistable, so the motor can be turned off. Since this will be battery powered, but with no solar panel, I want the lowest possible current draw into the motor. Speed is not important.
I ran across a video where the guy buys a tiny micro stepper motor, and drives it directly from the GPIO pins, claiming that the current would be no more than 10mA., and indeed it seems to work fine. No discussion of how the turn-off spikes are handled - presumably the GPIO protection diodes take care of that. Right.
I'm not so much interested in driving from the GPIOs, but the link to the motor he bought is no good anymore, and I don't understand what specs I need to look for to find one that performs similarly. When I go searching, I find some motors specify the "short-circuit" current. which I assume is Chinese for the stall current, but these are hundreds of mA, even for tiny motors, not 10mA. Some specify the coil resistance, and most, but not all, specify the voltage which is typically 5V, but sometimes 3-5V.
So should I look for a 5V motor with the highest coil resistance, or what exactly that would tell me the typical current draw while the motor is on and moving? Here's the video:
For low current, why even consider a stepper motor of any kind. A regular DC motor can easily do your design by using positive stops on the rotating component. Just drive the motor for sufficient time to hit the stop and turn the power off.
Use the mechanism from a battery powered wall clock.
A single AA battery will run for months.
Use a microcontroller and mosfet to turn the battery power on when you want it to move.
Connect a lightweight lever or flag to the minute or hour hand. Something made of balsa wood and paper will do. It's literally going to take minutes for your indicator to become visible, but you said speed isn't important.
That's not how you save battery. Speed is important. If you have 30mA motor that does the job in 1second, it's definitely better than 10mA motor that takes 10s.
You could look for tiny toy gear motors called "N20" or "M10". Geared to 30rpm and powered at 3.3V they draw something around 20mA.
There are also 2g servo motors readily available in online stores making your setup even more simple.
Thanks for the replies. I'll have to research your suggestions.
But with regard to servos, first of all, what does "2g" refer to?
Second, I have on hand an HXT500 servo. It is marked "5GR". Using a 1-ohm resistor and my scope, I've confirmed that it briefly draws 1A when first powered up. And it doesn't matter what the control line is doing. A friend has a different small servo, and it does the same thing. So I had ruled out servos because of this characteristic, in the hope that a stepper would not do that. And I assume a regular geared motor would also not do that.
Does anyone have a link to a motor that might work for me?
You seem to be frustrated because no one can offer a link to something you can go and buy. All my little motors are from some device that had a motor and was relieved to the motor and other parts. Go to a thrift store and find a child's toy with a motor and buy it and remove the motor and adapt it to your project.
So explain why you give so much importance for this? For the battery life it is not crucial. For some other parts of you circuit it might be. For the battery life you need to calculate average draw multiplied by time it takes to do the job.
My neighbor said I would need to get approval from the condo Board to do this. So I just got back from meeting with two Board members, and it turns out I should have done that before posting here. They would need a formal proposal as to why this is needed, along with information on the commercial sources and cost for the devices - for all 18 cul-de-sacs. And of course they wouldn't permit a hobbyist to make the devices even if there is no commercial source. Something about insurance. So I'm dropping the project.
I appreciate everyone's comments. I'm sorry I appeared to be such a dullard, but I just never used motors before, and, as is clear, don't know how the math and the specs work with them. Maybe I can figure it all out on another project.
And the neighbor forgot to ask about maintenance on your device. Welcome to the commercial world. The condo board is a commercial enterprise, but not necessarily a for-profit enterprise.