Big Johnson signal generator
The purpose of this exercise was to play around with the 4018 Divide by n counter (AKA Johnson counter) as a signal generator.
By summing up the outputs of the chip, a fairly crude triangle can be achieved. With some resistor tweaking, it can even approximate a sine wave fairly well.
A good example of this is found here.
In this experiment, all of the resistors are set to be the same
I sampled the output pretty much straight to Ableton. It makes a rather decent scope.
Its pretty noisy with lots of digital artifacts. It could be made cleaner with better tolerances in the resistors or maybe just using a D/A converter.
Additional wave forms can be created by using a transistor to switch the voltage to zero. The diode and transistor act in kinda the same fashion as the mickey mouse logic. Its like an AND.
A good example is also explained here. ANding with the clock gives a pretty interesting wave.
The output in Ableton looks pretty close.
The transitor can be driven by other pins ( Q1 or Q5)in the counter as well to generate a ramp. Oddly, to my ear, a ramp and a reverse ramp sounded pretty much the same. I suppose frequency wise, they are pretty close.
Finally, it would by a bummer if I didnt post the samples. Here is a sample that plays all three of the signals.
Thats about as far as I got experimenting with the circuit. I was hoping it would sound interesting with a 4016 switching all the inputs to the transistor to alternate the signals, but it didn’t really interest me in a circuit complexity/ sound randomness ratio. It would probably sound much more interesting with a filter after it to subtract all the crunchy artifacts. Perhaps use two 4018s, one as an LFO of some kind.
email any suggestions to robstave@yahoo.com