Humidity sensor to 7107

[Kailey]

Hi everyone.

I'm new to this forum, and have been involved in electronics for several years now (though not in university just yet). I'm guessing (correct me if I'm wrong) there aren't that many other girls on this forum, but oh well...

So I'm designing a humidity sensing and control system, based on the HIH-5030/5031-001 from Honeywell. Datasheet: **broken link removed** I already purchased two of these sensors from Digikey. They give an analogue output from about 0.5V to about 3V linearly proportional to humidity, depending on supply voltage. I would like to output the reading to the ICL7107CPL ADC to be read on an LED display (sorry I haven't gotten into PICs or AVRs just yet), but to show 10.00V for 100% RH, and 0.00V for 0% RH (instead of on a 0.5-3V scale). I tried an instrumentation amplifier without success... any other ideas?

I would really appreciate any help or suggestions!

Thanks!
~Kailey

 

[Wp100]

Hi Kailey

Welcome to the forum - noticed your enquiry was getting to the bottom of the page without any response.

Have seen that display chip around for years but never used it, so can only offer general advice.

The chip only needs 0 - 200mv for FSD of 1.999 so don't think you need to amplify the output from the humidity sensor.

A quick search lists some circuits which show how to set up the display for various input voltages, hopefully this will get you going.

ICL7107 / ICL7106 - Digital Voltmeter

 

[Kailey]

Thanks for answering.

I did actually build the 7107 circuit, and it will measure both scales, but my difficulty is with trying to convert the 3 volts or so at 100% humidity into 10.00 volts at 100% humidity (and all values below that). I built a circuit with a gain of about 3 with the TL084 op amp, but the output would always be locked between about 8-11 volts. Would you know of any way to extend the scale from 0.5V-3V into 0V to 10V?

Thanks!
~Kailey

 

[Wp100]

Hi,

Think you missed the last point - the 7107 only needs to receive a signal of 200 milli Volts to display 1.999.

Your sensor output of 3 Volts simply needs to be reduced by a potential divider.

With the 7107 its just a case of adjusting the input resistors to suit.
This diagram also shows which resistor to change
Led display digital Voltmeter - circuit diagrams, schematics, electronic projects