Homebrew Servo Controller Issues
April 17, 2010
I've been developing my own serial servo controller for the hexapod I'm working on, using a Microchip PIC16F74. It accepts serial input and controls up to 20 servos. The servos are connected in ports A, B and D. Power for the PIC is from a 9v battery via a 7805 regulator. The servos have a separate power supply from a 6v battery pack.
The problem I'm having is that the PIC seems to brown-out when the servos are running. Powering from the 9v battery I get random behaviour, powering directly using the Microchip PICKIT2 programmer isn't possible as the programmer turns itself off complaining about a power issue.
I can't see why the PIC is having power issues when all it's supplying is the pulse? Running anything over Port A seems to work fine, in a few cases I have the PICKIT programmer fail with just a single servo connected to the board on Port B.
Below is the simplified schematic of the board; I removed the TTL-Serial chip etc... Can anyone offer any thoughts as to why I'm getting this behaviour. Thanks.