Embedded C - Humidity Sensor Interaction

[05026652]

Hi guys,

First off I am very new at electronics and embedded systems. I have come from a Computing background but aiming expand my knowledge base.

Now the question in mind, I have an embedded project that uses a humidity sensor - now I am trying to figure out from a linear chart representing Typical Output Voltage vs Relative humidity, how I can achieve a value that would be used inside a lookup table.

Apologise if this doesnt make sense, I will try and clarify certain things as we go along.

Heres the datasheet where the linear chart is on, page 4
**broken link removed**

Thanks

 

[Vizier87]

Pardon me if I'm mistaken, but you want it to be: relative humidity versus voltage output, right? Have you achieved this?

 

[05026652]

Ai thats right, and no I haven't achieved yet. I have done something similar before (in class) where a datasheet was provided for a thermistor - and we needed to find the ADC value for temperatures ranging from 0 -40. We used an excel spreadsheet and using gradient values from the datasheet was able to do this. Now I need to be able to do this for the humidity sensor, however im not sure what I can do with the datasheet provided.

 

[Vizier87]

Here's the Voltage versus %RH graph:
**broken link removed**

But I'm not sure by what you meant by "how I can achieve a value that would be used inside a lookup table."... It looks like you just have to read the graph and re-produce the table for a certain range/resolution?

Regarding ADC, there are issues regarding reference voltage, so as to say if the Vref is 4V, therefore at 100% RH the ADC value is 255 for an 8-bit digital value. That is if you have to address to such issues.

 

[3v0]

Some notes.

Looks like table 2 has much of what you need to use a formula rather than a lookup table.

The zero offset is .826V and the slope is 31.483 mV/%RH.

Next you have to determine the voltage to ADC output. That has been done many times. If you want better results use an external voltage reference.

 

[05026652]

Ah thanks guys for sorting me out....I was just a bit concerned that simply using the graph to produce the answers.....needed to think inside the box this time !

Thanks