The water sensor circuit is based on a 555 timer circuit and come common electronic components. The water sensor is made by two metal electrodes arranged very close that a drop of water (liquid) will bridge them .
If the liquid ( water ) is very pure you may change the resistor value to 2.2m ohms and if the circuit is give false alarm sensing you may change the value of resistor to 220k .
This voltage doubler circuit use a 555 timer integrated circuit wired as an astable mutivibrator .This voltage doubler circuit can deliver only up to 50mA output current and above that current limit the output voltage will be reduced. The actual output voltage will be around 22V for a 12V DC input and also the output voltage will be a bit unstable. Anyway, for low current applications this circuit is well enough.
This tachometer circuit is designed using a 555 timer circuit and common electronic components. An electrical signal taken from the low tension side of the distributor is converted into a voltage proportional to engine rpm and this voltage is displayed on a meter calibrated accordingly .