Signal generators are too expensive if you are not a professional. They are frequently useful to calibrate a program or synchronise a circuit's operation. Think also to stroboscopic effects and calibrations.

One can generate an oscillating signal with a small Arduino program, but the frequency is limited to 1 MHz (less if one program with digitalWrite). The Kyocera Exo-3 oscillator, an old chap, includes a prediviser by 2, 4, .., 256. We added a counter by 128 (74HC4024) to get lower frequencies.

The result is that the following frequencies are available:

pin1 Gnd

pin2 3-5V

pin3 8M 4M 2M 1M 500k 250k 125k 62.5k

pin4 62k 23k 15k 7.6k 3.8k 1.9k 970Hz 488Hz

(second line has rounded values)

Specifications of the EXO3 say 4.5-5V, 7mA. We noticed correct operations at Lipo voltage, down to 3.2V