Often times when I am riding my motorcycle, I like to record the footage from a action camera mounted to the helmet. I use a GoPro style (FireFly 6S) camera to record the footage and the battery on the camera lasts 1 hour to 1 hour and 30 mins. My rides are much longer than that so I decided to buy multiple batteries. The batteries in my camera are the exact same as GoPro so decided to buy the higher quality GoPro batteries.The problem however is that in order to charge the batteries, I must individually place each battery in the camera and charge it via USB. As a engineer, I am too lazy to do that.
So I gained some inspiration from the DJI Mavic drone. When I bought the drone, it came with a hub to charge all the batteries. I really enjoy that feature as I can plug them all in and know that whenever I go out to fly, all the batteries will be charged for me. In this article I will show you how I build a similar hub for Go-Pro batteries.
Step 1: Design of the Circuit Board and Case
GoPro along with other action cameras run on a single cell Lithium Ion battery. These batteries usually have a management circuit inside with a temperature sensor and small contact connectors. There are a few aspects to a hub charger. First, there is a source of energy, proper charging, and status of charge. To keep things simple I designed the board to run off of 5 volts which is enough to charge the batteries to their 4.2v maximum potential. I went with a USB B connector because of its rigidity and high current rating. To charge the batteries to the proper voltage I went with the MCP73831 chip. It is capable of charging one lithium ion cell and is very small. The data sheet of the chip gave a sample circuit which I used for this build. My board will be able to charge 3 batteries so we need 3 of these chips and the corresponding components. Lastly, to connect the battery to the hub, I had to do some digging and found the male end of the connector which is inside the camera. The batteries have a 3 pin connector (GND, Temp, Power) but we only used the GND and Power pins to charge the battery.
I used KiCad to design a 30mm by 30mm 2 layed PCB which looks something like this. At the end of the article there is a link where you can download the GERBER files to send out for fabrication. The zip file you download can be uploaded straight to JLCPCB which will build you 10 prototype boards for $2 and ship the board to you within 48 hours. https://jlcpcb.com/
I also went ahead and designed a little case for the board which would make the whole setup look a little professional. Cad files also at the end ;) You will need to 3D print the top and bottom piece. In my case the top and bottom pieces both snapped on to the circuit. If that doesn't happen, add some glue to set the case in place.
Step 2: Fabrication and Parts
Parts List :
MCP73831T-SOT23-5 IC (3)
2.2k Ohm resistor 0603 (3)
4.7uf capacotor 0603 (4)
20 mA led diode 0603 (3)
150 Ohm resistor 0603 (3)
Through hole female USB B connector - right angle (1)
TE Connectivity 2199011-1 (3) *this is for GoPro Hero 3. Though newer GoPros use the same connector their orientation is different. So be careful.
2x3 2.54mm female header (1) *optional
solder paste, reflow oven, soldering station, 3D Printer and patience
As mentioned earlier the circuit board was sent out to JLCPCB. I have used other low volume fabrication companies before but JLCPCB has by far been the best. JLCPCB requires a .zip folder with all the GERBER files. You can download the zip file at the end. Once the boards arrive, inspect them for any flaws. I also created a case around the circuit board. The cad files for the case can be downloaded below.
Step 3: Building the Board and Case
The circuit schematic :
Steps to building the circuit board :
1. Once the board arrive, clean them using some rubbing alcohol.
2. With the boards cleaned, use a tiny flat head screw driver to add solder paste to all the SMD contacts.
3. Place all the components on the circuit. Every component except the led diode needs to be checked for polarity. Use the schematic to ensure polarity.
4. Place the components in a re-flow oven and melt the solder paste to attach the components.
5. Solder on the USB B post and the optional 6-pin 3x2 connector.
With the circuit built, 3d print the top and bottom piece of the case. And that's it. I've designed the tolerances so that the circuit fits snugly to the board. If its loose then use some glue to attach the case.
LED Status :
Flashing = nothing connected On = charging Off = fully charged
Happy building and I hope you enjoy the hub.