10 years, 2 months ago.

Best power options for a larger number of KL25Z boards?


Sponsored by the ARM University Program we using KL25Z boards to teach biology students embedded programming. A current class project involves the use of 64 microcontrollers that will talk to each other using a home-brewn network protocol using serial communication. As we don't have as many computers to run the boards connected to USB, I'm wondering about the best way to power the project.

Three solutions immediately come to mind: (A) Use of USB cables, connected to powered USB hubs (any cheap-ish recommendations? 64 devices in total!). (B) Use of coin batteries using the optional holder on the back of the KL25Z (how long would they last?). (C) External DC power supply and wires soldered to Vin/GND.

It's likely that the individual boards will need to be reprogrammed several times during the project phase, so anything that puts them into a place permanently doesn't qualify. And, of course, cheap as possible, that's another criterium.

Any hints?


After a lot of research into the cheapest possible solution, I think an external power supply with enough current would be a workable solution. This one for example (http://uk.rs-online.com/web/p/plug-in-power-supply/7262836/) delivers 5V with to 4A. If I'm not mistaken, the KL25Z takes up to 120mA. So with a power rail fed by one of those, I should be able to supply about 30 controllers.

Can anyone see a flaw in my thinking?

posted by Boris Adryan 05 Nov 2013

3 Answers

10 years, 2 months ago.

Get a 5V cell phone charger or power supply with the mini-USB connector on it. It'd take a bunch of those, but it'd work.

Alternatively, you can get sixteen 4 port powered hubs or nine 7 port hubs. Either of these should be able to support all boards being plugged into them since they'r designed for up to 500mA per port. The only think is you need to make sure the 7 port hubs have a sufficiently large power supply - the cheapos I've seen don't. I would be surprised if the board drew anything close to the 500mA port max, though.

Note that for programming, they'd have to be plugged into the computer separately unless you can keep track of which board is which MBED drive. They will all show up in the same way with only the drive letter being different (assuming you're using Windows).

Accepted Answer
10 years, 2 months ago.

The first question you need to ask is "do you need to connect all 64 controllers at the same time?" Can you get away with a smaller grouping of controllers e.g. 10 controllers at a time? The Powered USB hub is the way to go, Just check that your hub can supply the demand.

10 years, 2 months ago.

Good point. Yes, the 64 controllers would all need to be alive at the same time. The problem I found with most powered USB hubs is that I couldn't find any info on the total current they can supply. Therefore I was hoping for some user feedback.