signalsoundwave
I want to make a simple synthesizer as a start to audio electronics. I want to start with a simple square, triangle, and sine, which the user can vary the pitch.
Is there a simple circuit to do these? I know a square can be achieved with a 555 timer, but I don't know where to start on sine and triangle.
Off the top of my head, here's how I might consider approaching the solution.
The higher the square wave frequency, the lower the resulting triangle wave if you use "normal" integration circuitry. If you want to address this issue you could "filter" the square wave and use a peak measurment circuit to produce a "control" voltage that rises linearly as the squarewave frequency increases. This can be used to control integration rates.
Another method is to "examine" the amplitude of the resulting triangle wave and use this to control the amount by which the triangle wave is post-amplified - i.e. big triangle wave = low gain, small triangle wave = big gain. Maybe this technique and the variable integration method can work together successfully.
To make a triangle wave I'd use an integrator circuit formed around a current source and this current source could be designed to inject more current as the squarewave frequency increases hence keeping the output amplitude roughly constant. You'd need two current sources to make this work; one for the rise and one for the fall of the triangle.
Ultimately, you could make the rise and fall have different rates and therefore you'd be approaching the concept of a sawtooth waveform.
Alternatively you use a phase locked loop (PLL) to produce a frequency that is significantly higher than the square wave base frequency and use this higher frequency to control a sinewave/triangle/sawtooth look-up table - I think this is how Analog Devices make there DDS products.
Simple triangle-wave generator using two op-amps. One op-amp is configured as a Schmitt trigger, other op-amp is an integrator. You mention 5V, so I'll include the bias network needed for single-supply operation. Note that you have to use op-amps with rail-to-rail inputs AND outputs.
simulate this circuit – Schematic created using CircuitLab
Component values are NOT necessarily correct: R5 & C2 control the frequency. The ratio of R3 & R4 control the amplitude of the triangle wave - this also affects frequency.
Best Answer
Because the 555 charges the capacitor to 2/3 and discharges to 1/3 of the supply voltage, the extreme parts of the logarithmic curve don't appear. The resulting waveform is an approximation of a triangle wave.
It should sound reasonably close to a triangle wave. This signal can be found at the capacitor on pin 6.
An image search on "sine converter" will turn up a few circuits that convert a triangle wave to an approximate sine wave. There are a lot of parts in them, though.