Monday, July 26, 2010

A Digital Water Level Meter

Here's an analog water level meter that uses commonly available parts. The output is a voltage that is proportional to the water level.

The monostable is a 555, eg. LM555 or NE555, or could be a ICM7555, the CMOS version of the 555 for lower power consumption. The width of the pulses out of the 555 is proportional to the water level. R7 and C5 form a low pass filter to smooth the DC value of the pulse train. Their values can be increased to lower the cutoff frequency if dynamic response is not required. The lower the cutoff frequency the more noise immunity the device will have.

The zero offset is removed in the differential stage IC1B. The LM324 is a quad op. amp. that can be used in single supply configuration. The maximum output of an LM324 is about 1.5V less than the supply voltage Vcc. The supply can be from a 3-terminal regulator eg LM7808,LM7812, LM7815 - or LM78L08, LM78L12 or LM78L15. The voltage input to one of these regulators needs to be about 2V higher than the regulated voltage. For low power applications a micropower regulator like the MAX666 could be used.

The Link To Whole Project, click here