Audio Waveform Generator

thingiverse

This Audio Waveform Generator appeared in Maplin Projects Book - 48 (PDF of article included). I designed and built my own board using eagle software (eagle files included) and created a custom case for it with OpenScad. The board shown in the image is my initial attempt. The V2 board, which can be found in the associated files, fixes several issues including reversing the Frequency pot's wiring, moving capacitors C13-C16 to avoid hitting the nut that secures the attenuated BNC socket, relocating the power connector to prevent it from hitting the battery holder, and adding notches for the cables from the BNC sockets. The four trimpots are soldered on the back of the board for easy adjustment. The power and output connectors are also located on the back of the board. I used 1/8W resistors throughout to maintain a 7mm hole spacing. You can use 1/4W resistors, but they will be a tight fit. Assembly ======= To mount the PCB, drill holes with a 2.5mm drill and create threads using a 3mm tap. I used 6mm M3 screws to secure the board. Some of the other holes for the buttons and pots may require drilling or filing to ensure proper fitment. The power supply requires two 9V batteries providing a positive and negative supply. The power switch must be double pole single or double throw; place it between the +9V and -9V supply leads. The 0V or common lead does not need to be switched. I recommend soldering the LEDs in place after screwing the board onto the front panel, allowing you to push them firmly into their respective holes. The pots proved challenging to source. You will need pots with long shafts; standard 15mm shafts won't work. I obtained pots with 20mm shafts, but even these required knobs without a gap between their base and start of the hole. I purchased my pots from speed_mart on ebay (https://www.ebay.com/sch/speed_mart/m.html).