The site is no longer active, but I managed to find a copy on Web Archive and later Bill's new website
There are a number of flashing circuits based on 555 timers and both Dual & Quad Op Amp designs.
I've extracted the two images that I use the most and have been particularly good with Tim Escobedo's PWM and the above mentioned wah circuit.
|The resistor between pins 7 & 2 controls the rate.|
|I have used TL072 & 4558 chips in place of the 1458|
According to Bill's website, it can also be used as a straight up LFO without the LED and is good for up to around 10khz. I haven't been able to get it to drive an LED faster than about 1/3hz yet, but that's due to a lack of time & actual knowledge of electronics on my part (you don't need to know much theory in order to tinker with FX pedals & synth circuits).