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Digit hygrometer circuit diagram composed of humidity sensit

2014-11-16 01:31  
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Digit hygrometer circuit diagram composed of humidity sensitive capacitor
The figure1 is a digit hygrometer which is composed of humidity sensitive capacitor. 1KHz oscillator is made of G1, G2, it periodically trigger monostable trigger which is composed of G3, G4, the output pulse width is related to humidity sensitive capacitor. When the relative humidity is 0, the output pulse of monostable trigger is equal to oscillator's period; When the relative humidity is 100%, the output pulse width is 20% wider than it. The lasting time of G5-G8 XOR gates output humidity opposite pulse changes in relation to the humidity, the range is 0一100μs. In order to count the humidity opposite pulse, adding it and G12, G13, produced 200KHz narrow pusle to g9 input terminal, it produces narrow pusle only in the period of it has humidity opposite pulse. If it counts the humidity opposite pulse with 100μs maximum width and 50μs narrow pulse original sample, then the resolution is very low. So, it adds 200KHz oscillator's output pulse which is composed of G12, G13 to the input terminal of G9 and gate by 1Hz pulse singal of 4518(1)一4518(3) frequency division, it can obtain 500ms time. G10's output pulse is displayed the measured relative humidity by 4518(4)和4518(5) frequency division and decoding driver to drive 2-bit display. G14一Gl6 transmissive pulse is used to reset the counter.