Claudia:
So, I'm making a little x-y plotter, using the 28byj-48 5V steppers (with the drive module)It is all working beautifully .. But I really want to ask about power, as I'm finding this the trickiest to get right.
So I have been using some 9V batteries, into either the vin, or the dc in
The motor is 5V and runs out of the 5V pinIt would be very useful to know the worst case current demand for the two motors as there is a limit of how much +5vdc current you can draw from the arduino 5V pin and it's a different value if the board is USB powered Vs powered from the external DC power connector. Assuming it has been working for you except for short battery life I guess you may be OK, but it's best to always have and incorporate all the information required to make the best design decisions.
But, I have to replace the batteries fairly regularly... More than I'd like to since I am calibrating the drawing mechanism.
Those small 9vdc batteries were designed to power smoke alarms and other very low current devices, they really suck for arduino projects and they are the most expensive battery choice possible from a capacity Vs cost basis.
I got a 12V adaptor today, and ran that through the vin, and motor from the 5V. The DC plug and the little 5V regulator got hot, so I think it's possibly a not very accurate 12V, or else it really is just too much.
Tomorrow, I'm going to try to find an adjustable adaptor, or maybe a 9V. But I wanted to put the question out there about running quite low voltage things, like small steppers, but getting the appropriate power source.
What kind of solution did you find. Do you worry about the heat?
I don't worry about the heat, but many do. The on-board +5vdc voltage regulator has build in protection against over temp and over output current limits, it just shuts off it's output if either limit is reached. But that aside, heat is never an advantage (unless your building a heater
) so it best to try and run as cool as it can. The recommended input voltage for the Arduino DC connector is 7.5vdc to 12vdc. The closer your adapter runs at the 7.5v value the cooler the on-board +5vdc will run, as that is it's function, to 'waste' the difference of input voltage to +5vdc output voltage via heat dissipation.
The other thing I don't like is my adaptor seemed to 'surge'. Even though it was switched off at the mains, when I just plugged in the DC cable, I got a blink of lights. Any advice for stopping that kind of thing happening?
Not sure what you are seeing, but it could be the main filter capacitor inside the adaptor still retaining some charge even though unplugged from the AC mains. Not sure of a easy fix for that, unless you switch to a more modern switching regulator type power adapter, as they usually use a small filter cap(s).