I have recently stumbled upon a service called BatchPCB which offers cheap single run PCB prototyping. I’ve decided to give them a try since it seems safe for someone whose never designed a board from scratch. After some digging it seems like going to their supplier, Gold Pheonix, would work out cheaper if you’re looking at a design that’s larger than 35 inch^2. This requires a minimum order though, so for now I’m going to give BatchPCB a shot. I’m going to convert one of my old wire-wrap designs, a light controller, to test out this service and practice PCB design.
The purpose of this circuit is to control AC line voltage, specifically the brightness of an incandescent light connected to the controller’s output. It is based on the android architecture and has a similar structure, with the addition of input and output sections. The circuit design isn’t too complicated, the input consists of a pair of MSGEQ7 chips and the output is controlled through some optically isolated triacs. The next stage will be converting this schematic to a PCB layout and sending it out for manufacture. A summary of the circuit subsections is provided below.
This is essentially the power selector from the Arduino Uno board. I’ve explained it’s operation in a previous post. Its basic purpose is to switch between the external and USB power supplies as required I’m not a huge fan of this circuit, it’s over complicated and takes up a large amount of board real estate. It’s inclusion here was mainly an educational exercise and it will be redesigned or removed by the next revision.
This is a standard FTDI USB circuit. It provides serial communication over USB and allows for programming the target Arduino code.
Again, this is pretty standard. It is an AVR Processor setup in the Arduino bootloader. The processor ports have been brought out to headers to allow for easy access. Along side the standard TX,RX, and power LED’s there is an extra set of LED’s serving as an onboard VU meter of sorts.
My initial design had a set of filterrs in an attempt to perform beat detection on an audio input. Once I found the MSGEQ7 Graphic EQ chip I gave up on that path and switched to the new IC’s. They are much more compact and are pretty good at there job. In this design I’ve used two in order to allow for independent left and right channels. I’ve included some jumpers in order to link the inputs and control signals to allow for signal channel operation.
Zero Cross and SSR Output
This is an optically isolated section of the board which allows for control of the line voltage. There is a zero cross detector to inform the processor of the timing of the AC signal. Each of the channels can be independently controlled to any brightness level.