Resizable ARM Dev Board; Just Take Some Off The Top

[Bob Alexander’s] most recent project is a hack saw resizable ARM breakout board. He wanted to start using more ARM microcontrollers in his projects and went for a breadboard friendly design. It uses a 40-pin dip package, but if you need the horsepower but not the I/O you can literally cut it down to size. We might recommend grabbing some tin snips, which can cut through a PCB like butter, but to each his own.

The board is based around an STM32 chip. You’ll find a crystal oscillator for the system clock, and a clock crystal if you need it. On the other side of the chip he included a footprint for a voltage regulator. This setup provides a remarkable range of input voltages, accepting from 2 to 3.6 volts without the regulator, and up to 16 volts if the regulator is present. He designed a package footprint that can be easily bridged if there’s no SMD part there. Just make sure you insulate that pad if you are using one with a conductor on the bottom. He explains this in detail in his writeup.

You’ll need a programmer to work with the board. He uses an STM32 Discovery Board for this but there are quite a few other options out there too.

16 thoughts on “Resizable ARM Dev Board; Just Take Some Off The Top

  1. I for one wouldn’t cut it if it was at all possible but if you really had to I would use a Dremel with the thinest cutting blade I had.
    Using tin snips might fracture the pcb in a direction you don’t want to go and you just mucked it up.


  2. Hacksaw puts no stress on the board, tinsnips can flex a board significantly. And then there is the headers. Hacksaw, bandsaw, or razor saw is definitely better in this case.

    1. Macona
      I will have to disagree with using a hack saw. unless you put it in some kind of foam block to hold it. the downward pressure would bend the pins and may even crack the pcb.

      I would first mask off the rest of the device with cellophane tape and use the dremel that way the dust from grinding the metal traces and connection pins would not cause shorts.


      1. A hacksaw works very well. It’s much easier to control than a Dremel, and there’s zero chance of damaging something by slipping. Since you’re cutting through a PCB instead of a steel pipe, you don’t need much downward pressure, so bending pins isn’t really a problem.

    2. +1 I’ve been chopping up PCB’s for decades and I only use tin snips when I don’t care what happens to the board because they flex the board brutally and produce sideways splitting. I use a mini-hack when I do need to preserve the board, and it produces course dust.

    1. @Drone: Wear a mask and saw it outside? If you’re not doing this 24/7 it should be no problem as long as you have sufficient ventilation (and don’t leave any dust around to get stirred up later – thus, do it out in the yard.)

    2. Neat feature for a dev board. A while back I designed a project starting on the mbed, but at $60 each it’s a bit too expensive to use in production. I found the LPCXpresso 1768 board which is directly compatible by design, and half the price – but it’s huge (twice the size it needs to be, since each board includes a the STLink debugger circuitry.)

      However, it’s laid out such that you could just cut the board in half and remove the STlink, and if you were really careful, you could even re-attach it via headers. Pretty clever, although I didn’t end up cutting them, as I had enough space for the entire thing. Still it would have made some things a lot easier.

      Only concern is that the hacksaw takes a rather wide (~1mm) chunk out of the board, so you have to be careful going between headers and such.

      Also, thanks for the link about the personal edition of Crossworks, that might come in handy – I have several projects that I’ve been wanting to do, but I’ve been hampered by godawful IDEs (I’m looking at you, IAR!) and the code-size limits of the compilers (many of my projects involve TCP/IP stacks etc that are generally around 25Kb at least so an 8K compiler limit makes it useless to me.) I have at least three STM32 boards of various types that I may be able to utilize, and $150 is really reasonable if the compiler is solid. I only wish more companies had that!

    3. Derp. Meant that second comment to be in the main thread, but this forum software is a bit wonky, and returns you to the “reply” screen after submitting a reply, instead of the “new comment” screen as I was expecting it to do.

    1. Kalle, remember this is for hobbyist work, not commercial products. DIPs are useful because they can be used on solderless breadboards and in standard perfboards from (for example) Radio Shack.

      But even when using DIPs, it can be nice to minimize the size.

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