Circuits

High Power Scalable BMS

This was a really challenging and fun project. As the only electrical engineer on the project, I designed it from start to finish. This is a 4 channel Battery Management System (BMS) which is infinitely scalable due to the careful consideration of voltage domains. Each PCB has 13 voltage rails, the majority of which are isolated from each other. Everything is fed back to a microcontroller which controls the whole operation of the battery cluster and passes up state of charge to a master controller. The circuit is capable of bleeding power to balance the batteries or feed in up to 10A of balancing current to each individual cell. All current in or out of the cell is coulomb counted and voltage is measured with extreme accuracy to track the exact state of charge at any given time.

Low Voltage Current Shunt

On the surface this was not a complicated circuit. In practice, it was rather difficult to pull off. This is a balancing circuit connected in parallel to a single battery cell in a system. It is powered entirely off the cell and is capable of bleeding off 20A of current from the cell to avoid overcharging. The voltage level it maintains is fully adjustable and it is capable of sinking 20A, even when the cell voltage drops as low as 800mV, with no external power and only 15 analog components.

Helpful Circuits

These are three helpful little circuits I find myself putting in lots of my designs. The first is a low loss polarity protection mechanism, the second is a combination low loss polarity and arc protection circuit to be gentle on connectors in hot swap applications and the third is a low loss DC only rectifier circuit to make a DC input polarity independent. Click here to download the schematics.

USB Powered Headphone Amp

I have a fondness for some of my old, wired headphones and some of them don't get driven properly directly from my cell phone. Since I wasn't ready to retire them I decided to make a small, clean amp I could integrate into my bag. The amp itself lives on the strap (on my left shoulder) and gets fed audio and power from a bluetooth receiver and USB battery pack in the bag. This setup makes my headphones sound great, cleans up the wiring, frees my phone from wires and also gives me easy access to adjust the volume even with gloves on (important when riding the subway in winter). I've been really happy with the whole setup. Headphone Amp - Schematics Headphone Amp - Gerbers

Trailer Adapter

I made this circuit for my Subaru back before off the shelf trailer adaptors were readily available. This circuit creates a 4 pin trailer plug out of a vehicle that has dedicated turn bulbs. Basically, it consolidates the tail lamp, brake lamp and directional lamp into a tail and brake lamp which is compatible with most trailers. All power for the trailer lights is pulled directly from the vehicle battery and the existing vehicle lights are used for signals. I've had this installed in my car on a protoboard for over 10 years and it still works great!