Click on the picture to see a larger picture, with the schematic diagram above and the circuit diagram below. It is now painted.

The oscillation frequency f =1(1.4 * r * c), c is the capacitance C 1, r is the sliding resistance R2, and C 1 is fixed. If the resistance of R2 is adjusted to about 2.85K, a square wave of 250Khz will be output at four pins. R 1 is a matching resistor, which is generally unnecessary. This is 10K.

There are few devices: a chip 4069 (which can be replaced by 7404), a capacitor 1nf, a resistor 10K and a 5K potentiometer.

Finally, remember that the power supply of the chip is 5V.