After learning that older CRT oscilloscopes could be used to display intricate wave shapes and frequencies of audio signals from MP3s, I started looking more into analog/digital synthesis.
While I don't own an oscilloscope at the moment, I do have a solder gun and various tools. I found various tutorials and how-to's online and was overwhelmed with how many things you could create; such as voltage controlled oscillators (VCOs), voltage controlled amplifiers (VCAs), low frequency oscillator (LFO), and so many more.
I found a really interesting design by Cosmic Garden, which incorporated the following:
Atari Punk Console
The main integrated circuit in the Atari Punk Console (APC) is the LM556, which contains two independent 555 timers. The 555 timer has two operating modes: a monostable and astable mode.
The monostable mode is used to produce a single pulse with a set length in response to a trigger input. The circuit will stay in a low state (value of 0) until the chip receives a trigger input, hence the name "monostable".
The astable mode does not have a stable state (kind of obvious, right?). The output of the chip is continuously switching between a high and low state (value of 1 and 0) without receiving any trigger input from the user.
The APC utilizes two 555 timers or a single 556 timer, for this project, I decided to use a single 556 timer as it's what I had laying around at home. The 556 IC contains two independent 555 timers which will both be used in this project. The first timer in the 556 chip will operate in the astable mode and the second will operate in the monostable mode. The reason for this is that the first timer will drive the second timer, which is in a monostable state that requires a trigger input.
MS-20 Sallen-key VC LPF
Tim Escobedo made a LP VCF similar to that of the Korg MS-20's LP VCF. The purpose of this filter is to remove any upper harmonic elements from the output of the Atari Punk Console. You could plug in any signal to the LP VCF, but for this project, it will be the APC. This filter utilizes a LM13600 operational trans-conductance amplifier at the core of the circuit.
Back in the 70's there was a column in a magazine called 'Captain's Analog'. The column that I am basing the design off of is The Baby 10 Sequencer. It is a 10 step analog sequencer that has various uses. It has a potentiometer for controlling the level of a control voltage and a pulse out for each step. So how does this interface with the other two circuits aforementioned? Let's get into the circuit operation and find out.