Sew Circuit

Find a spot on the harness/backpack for your circuit. The GPS needs to face the sky (through some fabric is ok).
Stitch FLORA to the fabric around one of the GPS pins used in the circuit diagram (we chose RX to stitch first). Leave about a 6-inch tail of thread (we'll tie it later). Make several stitches around to create a secure mechanical and electrical connection.
Don't cut any thread yet, and position the GPS module next to FLORA.
Continue stitching with the same thread to connect to the GPS' TX pad. Loop several times around and then tie the working thread to the tail you left earlier.

Make a tight double knot!
Dab a tiny amount of clear nail polish to the knot you just made. Try to get it only on the knot! Hold the threads taut at different angles for better access with your brush, and try not to get any polish on the pads of FLORA or the GPS.

Tug on the knot while the polish dries to tame that springy stainless steel! Leave long enough tails that you can tug on them again later-- don't cut them super short yet.
Repeat this stitching process to connect FLORA's TX to the FLORA GPS' RX, and likewise with 3.3V and GND according to the circuit diagram.

Double check your knots again, adding a tiny bit more nail polish if any of them aren't staying tight. Once the nail polish is completely dry, you can cut your thread tails very short.
Check your connections using a multimeter on continuity mode. Touch the probes to the pads on the circuit boards, not the thread, and check to make sure there is continuity between all four connections, and that there aren't any shorts. For more info on using your multimeter, check out our guide.

While the GPS doesn't have to be as close to FLORA as pictured to work well, it also shouldn't be too far away or the communication signal will degrade as the thread length increases. We recommend keeping them within six inches of each other.

At this point you can test the GPS the same way you did in the FLORA GPS guide, and verify your GPS is communicating with FLORA over the conductive thread!
Next add the coincell battery holder. Sew the + side to the FLORA GPS' BAT pad, and the - side to GND. This battery helps the GPS acquire a fix more quickly upon starting up, since it helps the GPS remember which satellites it connected to last time it was on.

Knot, seal, and snip the thread tails as in previous steps.
The 3xAAA battery pack will live in one of the pockets, and we've taped it up to provide extra strain relief on the wires and prevent the switch from getting toggled off inside. The wire passes through a small hole we snipped, then under the sewable battery holder and over to FLORA's JST connector.

You can even use a safety pin to affix the gaff tape to the inside of the pocket, so it doesn't shake around when the dog runs.
Lastly, add a piece of vinyl if your circuit is exposed. This will prevent the circuit from catching on branches, and provide a dampness guard against wet grass and slobbery dog friends.

We built the circuit right up top so you could see it better, but it would work just as well sewn entirely into one of the side pockets. The conductive stitching doesn't go all the way through the padded harness; it just pierces the top layer, so no threads are touching the dog's fur.

This circuit is not waterproof and should be removed from your dog before swimming or if it rains.
This guide was first published on Jun 04, 2014. It was last updated on Jun 04, 2014.
This page (Sew Circuit) was last updated on Jul 08, 2020.