The finished HSFG project, as published. Read the complete article 20Mhz Function Generator View the Schematic Diagram. View the PCB for the published version in 300dpi GIF format View the PCB for the simpler PCB mount version in 300dpi GIF format. My first HSFG prototype My first HSFG prototype. A double sided board with everything PCB mounted. YES, those electro's are hanging over the edge of the PCB. I didn't have anything else available, and Jaycar was closed !. This one didn't have the TTL output, that was a last minute inclusion in the second prototype that was published, hence the oversight described below. Notes & Errata There is a problem with the TTL output when the generator is used on the LOW and MEDIUM frequency ranges AND the MAIN frequency adjust control is set to the lower 15% of it's range. Any significant loading on the TTL output will cause it to osscillate on the positive and negative edges. This is apparently an inherent problem with the MAX038 chip !. The only solution is to buffer the SYNC output of the MAX038 with a 74HC14 schmitt inverter. This can be mounted on a small piece of vero-board along with R10 and a bypass capacitor. Use the other 5 inverters in the package in parallel to provide a high current buffered output. Be sure to connect the supply pins of the 74HC14 directly to pins 15 and 16 of the MAX038.