High side switching

A project log for Binary clock rebuild

A nicer version of my AT90S1200 binary clock

DanielDaniel 06/16/2017 at 23:270 Comments

I'm using an old board I designed to sink 8 channels through mosfets. The board has its own switching regulator for the micro and up to 8 2-pin JST-PH headers that provide Vin (up to 20+ volts, 5V in this project) on one pin and switched GND on the other. but this project needs high side switching. The only ones I had were some surface mount MMBT2907A's. After some careful soldering and heatshrink I have a cable that switches 5V from the blue to the red wire when you ground the control signal. A 0603 3k3 resistor limits the base current. I don't have a lot of through hole.

The back of a scrap PCB served as a non-flammable surface to solder on.

The two wires on the same side of the transistor feel surprisingly firm, but the red wire is not as confident. Hopefully it will be strong enough. It works!