need help with humidity sensor HIH 4000-001

Other Hardware Sensors
1

Hi all,
I m using Honeywell humidity sensor called HIH 4000-001, the sensor is connected to mcp3204 A/D IC and further this ICs SPI o/p is connected to mega 2560.
My question is i cant able to get stable reading from sensor what to do for this??
I checked sensor o/p with multimeter bt mV o/p is very unstable e.g. 2000mV to 2060 and again 2060 mV to 2000mV and continue this process.. Is it sensors fault or anything else??
Please help me to stable this o/p or can i do any thing to smoothing or filtring this unstable mV o/p..??

2

Do you use 5V for the sensor ? Where is that 5V coming from ? If you use USB power, the 5V is not a good 5.0V.
You can test that by using an external power supply for the Arduino Mega 2560 board, and the 5V pin to power the humidity sensor.

3

dear peter,
Thanks for your reply. i cheked all power supply mostly i connect it with the laptop usb and as u mention it is very much stable.but still i cant find the solution on how to get stable mV output.

4

With an external power supply I ment for example a wall wart of 7.5V to the barrel jack of the Arduino board.
Did you measure the voltage when powered from the laptop ? You can measure the 5V pin of the Arduino. If it varies between 4.85 and 5.00V, that is the 3% I'm looking for.

It is also possible that some noise is in the circuit. Do you use long wires ? or a bad breadboard ? Perhaps you can take 5 to 20 samples and use the average.

5

Hii peter
Thanks for your valuable rply but i have a question that what u mean by "milli() is used for futur reference" ???

6

Hello

If you take a look at the data sheet, you will see that the HIH4000's need a load resistor of not less than 80K between 0V and output (check this as off top of head) - I have set one of these up and there are no problems with readings (approx 0.8V @0%RH, 3.8V @ 100%). In fact very stable.This is running on about 20cm hookup wire, but I wouldn't envisage problems up to 1m.
Take care you get everything wired up right as expensive bits of kit, assuming the genuine article.
Your 2000mV about right, approx 45%RH?