Resolved - How to make use of belly connectors on TinyFPGA BX?


On the underside of the TinyFPGA BX, there are two connections, which I refer to as “belly connectors” for lack of better term. It is completely undocumented how to make use of these connections.

I have surface-mount IDC pin header strips which mate with these pads; however, trying to solder to them is a right nightmare as the pins just keep moving. There’s no guarantee of alignment. I tried to make my own jig to hold the strips in place, but again, to no avail – now there’s insufficient room to even just tack them in place with the fine-point soldering tip I currently have.

So, how does one make use of these pins, without the expense and long-term reliability issues of pogo-pins?



There are pogo-based breakouts that have been linked around or can be found via google. Otherwise, you can solder it them, it just requires some patience and finesse. Use small gauge wires, strip less wire than you think you need, pre-tin the wire and the pad, try to fold the wire at 90 degrees so it doesn’t touch other pads.

Here’s mine (excuse the cat hair):


To add to that, there’s a decent and relatively inexpensive breakout kit on Tindie:

It’s a royal pain soldering the connectors but it can be done.


That’s definitely the easier way–he’d mentioned he didn’t want to use pogo pins, though–but it’s definitely good for anyone reading this to have the link!

Unfortunately for OP, that really just leaves the option of soldering, though.


The pogo pins are only relevant for the auxiliary pads (RST, WP, 1.2v). Most of them are IDC header type. They’re a pain but the trick is to get one pin tacked down aligned right, then work the rest. A (gentle) soldering holder makes quick work of it.

Edit: imho once you get one pin aligned, the breakout pins are far easier to do than individual wires. I’ve done that before and it’s a greater pain, especially if one in that nest has a bad joint or breaks later.


wow, I have no idea how I missed that they were using a surface mount header! that makes WAY more sense! That said–I’d definitely recommend OP goes with this solution.

edit: I guess the only downside is that it’s less breadboard friendly with that large breakout.


Since I’m making an electronics kit (think RC2014), this is not really scalable.

But, I believe I’ve found a solution to my problem.

  1. Solder on the 14-pin outer/through-hole connectors. It’s important that they be soldered for mechanical stability in later steps.
  2. Insert two pins of the surface-mount pin header into female strip socket.
  3. Insert the female strip socket cross-wise on the TinyFPGA’s through-hole pins.
  4. Insert another strip socket a few pins away to lock in the registration.
  5. Now you can solder the ends of the surface-mount connector to the board with full confidence that they’ll line up correctly with the socket on the PCB.
  6. Scoot the cross-wise sockets down, and solder the other end of the surface mount socket.
  7. Now you can remove the cross-wise sockets, and solder the remaining pins.


Too expensive, and too big, for my purposes.


Re: your edit – exactly where I was headed. I just didn’t have a step-by-step method of achieving that goal. But, I have figured it out, and posted a quick set of instructions above.


That’s quite clever - I don’t know why that didn’t occur to me when I did mine, but I wish it had!

As for the breakout side and cost, it wasn’t too prohibitive for me as I had no plans to create a custom board to slot it into and just wanted everything broken out. It looks larger than it is, maybe a bit wider than an ESP32 devkit (the outer two rows of holes on each side can be broken off).

Finally, when it comes to using a wider board with a breadboard, I like to just put two breadboards side by side (or use a pre-built multiboard protoboard) and straddle two of the individual boards that make it up. But again, whatever works for what you have handy.