F to V conversion for a water level pressure transducer

Discussion in 'The Projects Forum' started by stevemcd, May 8, 2013.

  1. stevemcd

    Thread Starter New Member

    Mar 8, 2013
    I have a recovered pressure transducer from a washing machine. AIr pressure in a tube immersed in the water bowl increases as the water level rises, and drives a diaphragm that moves the core in an unknown inductor. The simplified circuit is attached.

    It is a tank circuit that drives a 4069 based oscillator. Originally it measured up to a metre of water and the changing signal frequency was used to evaluate water level. I intend to use the same transducer to measure water level in a tank about 3 metres high, so I will alter the spring pressure on the diaphram to change the range of measurement. I think the best way to interpret the transducer output is to convert the signal to a voltage with something like a Texas Instruments 2917 frequency to voltage converter. I'll later use an ADC and log levels via a PC, either through a data logger or directly on a server.

    The signal looks to centre around 6kHz at idle (empty) and seems to range to 20 kHz full. I need help designing the F to V conversion, beacuse I don't have enough knowledge to interpret the datasheet for the 2917 and develop a practical convertor. I'd like to acquire not less than 20 level readings over the full range of the transducer. Can someone point me in the direction to get started on the F to V design?
    Last edited: May 8, 2013
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Sorry for stating the obvious, but why not forget the freq->voltage conversion and just work in frequency?

    If the eventual goal is to send data to the PC you can just measure the frequency directly with a PIC or other micro, convert it to 1 byte, and finally send that byte to the PC on the serial port?

    All you need is a cheap PIC like an 8pin 12F629 and a few lines of code. :)