These days the unijunction transistor (UJT) is not common, but IF you have one you can mount this low frequency oscillator. Very low frequencies in the range of 0,0001 and 0,1 Hz can be generated by this circuit depending on C. This capacitor can have values between 100 pF and 1 000 µF and the frequency adjustment is made by P1.
Unijunction Oscillator
