After a number of requests from people, I decided to build a small batch of battery boards for sale. I re-designed my board to pack as many useful features as I could without adding too much complexity to it. My original board used a mechanical slide switch to turn it on and off. I liked the simplicity of the slide switch but it was the most expensive component on the bill of materials. I decided to replace the slide switch with a push button feature to toggle power on and off. The push switch design was borrowed from a circuit that is sold at Adafruit. I played around with the design for a few months before finaly pulling the trigger and having 100 boards made by Seeed Studio. With any luck I should have a small batch of boards to sell some time in January. I’ll add a link here when I get some kind of store set up.
If I ever make bigger batches of the board I will probably have to panelize the design. At this point I didn’t want to have to buy an upgrade to my Cadsoft Eagle license or figure out how to panelize straight from ther gerber files.
For stencils, I went to OSH Stencils. Prices from OSH are very reasonable and they deliver quickly via US mail. I made a simple jig to hold the boards in place while squeegeeing solder paste over the stencils. My jig used some milled out pieces of scrap printed circuit boards with double sided tape on the back to hold them to an acrylic panel.
To populate the boards I put together a simplified (semi-automatic) pick and place robot – this part of my project took about 8 months and was a project in itself. I will post information on the robot build when i get the chance. To hold the boards to the PNP robot I used a set up similar to my stencil jig. With my current set-up, I have enought table space to process four boards at a time.
After placing all the little parts on the board with the robot it’s off to the toaster reflow oven. This is another project I have to get around posting some of my build photos on. The oven temperature control is based on the Rocket Scream Design but uses a Nokia LCD for the display. Under the display is an Arduino pro-mini controlling everything. This picture was taken while I was testing the oven control loop.
My first project with the new boards was a portable internet radio using the PiTFT board. The speaker I used for the project was a Samsung cell phone replacement speaker I sourced from E-bay. Lots of sound from such a tiny driver.
You can see in the video I have a small wired plug that is being used to power the speaker amplifier board. I’ve added a small switched power port (solder pads) on the side of the battery board. The power port breakouts give access to switchd 5V and battery (~3.7V) power. There is also a pin breakout for the power switch so a remote power button can easily be implemented.
The battery board now has three different methods for connecting a Li-Ion/LiPo cell to the board. The fist method is a direct wiring connection provided by a pair of solder pads. The second method is a JST plug connector. The JST connector provides a way for pre-wired cells to be used – if they have correct polarity. I’ve set the JST plug polarity so that it matches the Li-Po cells that Adafruit sells. The third method is a spring contact specifically designed to use a Samsung Galaxy S III (or equivalent) battery. This is the type of battery connection I am using in the video.
The charging method on the new board hasn’t changed from earlier designs. I am still using the MCP73831 chip to control the charge from the mini USB port. Next to the red power LED is an amber LED that is lit while the battery is charging and goes out when charging is complete.
Here are a couple of close ups of the new board:
Notice the warning about the type of cells that can be used.