This is a very Function Generater project. can be used Triangle and Squarewave Generator. The main parts are CD40106 popular CMOS IC and a normal transistor is BC547 or NPN type such as : BC549 , 2N3094, 2SC1815, OR an Old number 2SC458 .
VR1 For Control frequency Output. S3 to Seclector High = 1kHz-10kHz, Low = 10Hz-100Hz. Voltage supply 3-15V.
As you see the circuit in figure 1. The IC1/1 -CD40106 is inverter HEX Schmitt Trigger as CMOS-IC Which works with other electronic devices, to signal oscillator generators on square and triangle waveform.
The square wave output is determined with R1,VR1,C1 and C2 that the level of frequencies depends on time that the capacitor charge currents. So if we increase the capacitance and resistance up the frequencies will reduce down.
The switch S1 for choose between frequency high or low. When S1 is on LOW position capacitor C1 is connected with C2 makes the output frequency as form 10Hz to 100Hz. And then S1 on High range, At this time the C2 be connected to the inputs of IC1/1 only so there are the output frequency from 1KHz to 10KHz. And VR1 use for adjusts frequencies in these range LOW or High.
The second section is the triangle wave has been derived from the charging and discharging of the capacitors (C1,C2). And to avoid the load capacitor, therefore buffer supplied by transistor Q1,that is connected on a common collector form. This output is voltage drop across R2 which the range lowest of waveform will higher than level of zero voltage by changing the level of the power supply.
Adjusting VR1, the frequency of the square wave and triangular wave will change with it. And has with equal frequency.
This circuit have the disadvantage of low current. You should add an amplifier to a good system. Although the structure protected internal a short circuit. But it may not be enough. For real applications.