As we are wrapping up the 3rd “revision” of the basic voltage divider I thought I’d write a post to bring everyone up to speed.
For those of you that aren’t familiar we use a voltage divider to get the battery pack voltage to a measurable level so that it can be read by the controller without frying it. For the arduino nano that we are using right now the max analog input level is 5v. Since we are running 12 or even 14 cell lipo batteries at up to 60v that is obviously way too much for the arduino to handle. The voltage divider takes a 60v charge and steps it down to 5v. The key is that it is proportional, so 30v would output 2.5v etc. There are lots of calculators that you can use to figure out which pair of resistors is right for your desired output. You can play with one here
The first batch of OpenPPGs was small and we were able to use stripboard and hand solder the voltage divider circuit. These were very basic and only included the voltage divider. Obviously we didn’t want to hand solder these circuits for mass production though.
We designed the first PCB and we were pretty happy with the results (for the voltage divider part at least) so we shipped them with the batch 2 orders. Here’s what the PCB looks like.
Notice that there is more than more than just the voltage divider resistors (R3, R4). We also wanted to be able to power the Arduino controller using a voltage step-down to provide 12v. It turns out that I miscalculated and we were trying to draw way more than the linear regulator could handle so it got hot and was not stable enough to feel confident in shipping with it enabled.
Thankfully we had a supply of sizeable BECs that could handle powering the controller and much more so we included these as a nice upgrade with batch 2
As I said in the beginning we are now wrapping up the 3rd revision of the voltage divider and the second PCB.
As you can see it is quite a bit more complex (and there’s even more on the back).
While the voltage divider has remained the same we have completely switched the way we are stepping down the power for the controller. To handle more amperage we are now using a buck converter. This allows us to be lots more efficient and provide extra amperage for expandability. We’ve also centralized connections for all of the ESC signal wires to connect to. This will help clean up some wiring and make parts easier to swap out. Production of these PCBs will start in the coming weeks so be on the lookout for updates.
If you’d like to learn more or have input feel free to chime in below or send me a DM.
EDIT: Updated with final batch 3 frame PCB design