Although a PCB isn’t required to successfully build one of these receivers, it will make the task easier and also eliminate potential problems due to layout and wiring. Included with the PCB archive is a bit-map image that can be used in making a single sided PCB. The single sided board requires the addition of seven jumper wires, but this can be reduced to two short ones if a double sided board is made, but at the expense of increased fabrication effort. If the two sided approach is desired, I’ve provided the double sided layout files generated by the DOS freeware version of Protel’s Easytrax PCB layout program.

PCB’s are fabricated out of copper clad PCB board stock by first applying a mask layer to the copper surface that matches the layout pattern, then chemically etching away the unwanted copper using a Ferric Chloride solution. Finally, the tedious task of drilling all the holes for the components completes the process.

Two general methods are available for home-brew PCB fabrication. The first uses special "Toner Transfer" paper, onto which the PCB image is printed with either a laser printer or copy machine. The printed image is then thermally bonded to the copper clad board stock using a clothes iron, after which soaking in water dissolves a layer between the image and the paper, leaving the toner attached to the copper surface, which serves as the etching mask. The other method uses PCB board stock that has been treated with a photo sensitive resist mask layer. The PCB image is printed on a sheet of transparency film which is then used to expose the photo sensitized PCB stock. The board is soaked in a chemical developer which removes the unwanted resist, leaving a mask pattern matching the layout. The boards from either process are then placed in the ferric chloride solution to etch away the unwanted copper. The materials for either method are going to cost about the same, which will be about $20 - $25 to produce one to four boards. Now I’ll offer my opinion. I’ve tried both, and found the photo method to be pretty fool-proof. The toner transfer method requires a laser printer that can print a very dark and heavy image, and getting the complete image to bond to the copper is a bit tricky, and will likely take several print/iron/soak attempts before a board ready for etching can be produced. Probably the best source for the chemicals and pre-sensitized boards is going to be a local electronics supply store (other than Radio Shack). Toner transfer paper is readily available from the mail order firms identified in the parts list.

The bit mapped image file provided has a resolution of 600 dpi, and using a graphics program, can be printed to either the toner transfer paper or transparency film. The board is about 2.25" x 3.125". An easy way to verify correct scaling is to measure the distance between guide holes on the outside leads of U5 (28-pin PIC). Lead spacing is 0.100" on all IC’s.

Drilling the holes is best done using a high speed Dremel type tool, preferably with the drill press attachment. The PCB layout contains guide holes that will get etched out of the copper, making drill centering much easier. The following table lists good drill sizes to use.