Pic hygrostat

[dr pepper]

I have a phillips humidity sensor 2322 691 90001, its a capacitance type sensor.
I was wondering whether or not to bin the phillips sensor and use a dht11 sensor with built ins erial interface, it seems to be popular at the moment.
Anyone used a dht11?, seems like an easier way out software wise, the phillps sensor is just a variable capacitor, so I'd need an oscillator circuit and software ferq counter and the sensor isnt linear so I'd also need lookup tables etc.
The only thing is that the dht11 isnt meant to operate below +10 degrees, and this sensor might have to operate outside.

 

[jpanhalt]

I the phillps sensor is just a variable capacitor, so I'd need an oscillator circuit and software ferq counter and the sensor isnt linear so I'd also need lookup tables etc.

Have you seen these two application notes:

https://www.electro-tech-online.com/custompdfs/2012/09/00611b.pdf

https://www.electro-tech-online.com/custompdfs/2012/09/01375a.pdf

The first describes how to measure capacitance with almost any PIC. The second needs a PIC with the CTMU unit.

John

 

[dr pepper]

I've never looked at the ctmu before, looks like a versatile module.
The variance of the phillps sensor per %rh is less than 1pF, even the ctmu module will need very carefull design to discriminate such small changes, allthough it looks as though it'd do it.
The dht is looking better all the time.

 

[dr pepper]

I just found this application from phillips:

https://www.electro-tech-online.com/custompdfs/2012/09/Sensor_Humidade.pdf

It uses a 4001 as an osc with the sensor, also it uses another osc made from the same 4001 as a linearization circuit, the 2 outputs are mixed, I wonder if I could use the 2 comparators of a pic to do the same functions, and have a frequency output rather than rectify it.