Quote Originally Posted by BillsGU View Post
What ripple frequency was your Pi filter designed to decouple?
The 50hz of the power supply I use. I also found placing a small ceramic cap across pins 1 and 8 caused a weird feedback frequency. The best I have so far found is to have a sizable 12 volt gel battery with a an IC7809 to regulate its output. This gives me the option to run a Bd139 as an inverting switch on the 555 output to get a nice AC Square wave. I am now playing with different configurations to get a smooth enough signal at frequencies between 30hz and around440-480hz. I found that around 270hz is 100kph.