Building a simple humidity measurement circuit?

[pranav81]

Hi there.I have been browsing this site for a couple of weeks now.I am sure that you will be able to help me to construct a humidity measurement circuit.
The main requirement of the circuit is that that the current humidity should be displayed on a LCD/LED display.
I have searched in vain over whole internet regarding the same.I havent have had success so far.
I hope you guys will give me a helping hand and help me to the end.
Thanks in advance.


:ranav::

 

[John Sorensen]

Have you found a sensor? Sensirion makes a good one-- digital interface. Relatively inexpensive (humidity sensors are not cheap).

j.

 

[pranav81]

Well......sorry.But I have to build the circuit from scratch.I want everything from the basic circuit diagram.I am new to electrnonics world.I would be happy if you guys help me through this project that my college has assigned to me.



:ranav::

 

[Nigel Goodwin]

Well......sorry.But I have to build the circuit from scratch.I want everything from the basic circuit diagram.I am new to electrnonics world.I would be happy if you guys help me through this project that my college has assigned to me.

John Sorensen wasn't suggesting you buy a ready made unit, just the actual humidity sensor itself, then build your meter around that. It's normal practice to buy sensors, rather than try and build them.

If you need to 'build from scratch' to that extend you will have to make your own transistors and resistors as well :lol:

 

[John Sorensen]

I think to make a humidity sensor, then, you would take a hair, tension it with a spring, attach a slide wire, you could fashion a sort of potentiometer by laying down some carbon... no, wait, that's going back too far...

j.

 

[pranav81]

Sorry guys,if I have been sounding funny.My professor gave me this project.I found a dew sensor circuit on the internet.But he said that he needed a circuit that can display the humidity of the atmosphere on LCD/LED diplay.

About sensors,well,I have read a little about them.I understand that they work on capacitance principle.As I live in India,and more importantly in small city,I will have to rely on the sensor that my electronics dealer makes available.I am sorry that I dont have other options there.

So guys,I would be glad if you would point me to a circuit,which is simple enough for me to understand.

Waiting for some information.

Thanks.

:ranav::

 

[Nigel Goodwin]

Sorry guys,if I have been sounding funny.My professor gave me this project.I found a dew sensor circuit on the internet.But he said that he needed a circuit that can display the humidity of the atmosphere on LCD/LED diplay.

About sensors,well,I have read a little about them.I understand that they work on capacitance principle.As I live in India,and more importantly in small city,I will have to rely on the sensor that my electronics dealer makes available.I am sorry that I dont have other options there.

So guys,I would be glad if you would point me to a circuit,which is simple enough for me to understand.

As we've said all along, we need to know what sensor you are using, so obtaining a sensor should be your first job. Along with the sensor you should be able to get a datasheet explaining how to use it, and giving example circuits.

A quick google found this

http://www.humirel.com/Humidity_temperature_sensors.php

, one of many sensor manufacturers.

 

[pranav81]

Hi Nigel.Thanks for the link.I will have to visit my electronics store and find out which sensors do they stock.

BTW,could you guide me to a cheaper and good working sensor?I will then be able to at tell the store what exactly I need.

Thanks.


:ranav::

 

[grrr_arrghh]

if you have to buy it from your local store, go in and ask them what they stock!! theres no point finding a part, for them to say "no, we don't stock that"...

 

[Oznog]

I have experience in this area!

Humirel makes a couple of good sensors. The HS1100 or HS1101 are capacitive sensors, the best way to read them is to use its capacitance as the source for a 555 oscillator and count the frequency output. The data sheet has a well documented solution, including temp compensation. The freq output relationship with humidity isn't totally linear, but a microcontroller can certainly adjust for it if you want to be quite accurate. The microcontroller is the easiest way to implement the counter & LCD driver together anyways.
https://www.electro-tech-online.com/custompdfs/2004/08/HS1101.pdf

There is also the HS1500 module, which conveniently includes all the conversions so it could be quite easy to directly connect to a LCD meter designed to take in an analog voltage. It costs $33.40 compared to the $9.75 for an HS1101.

 

[pranav81]

Thanks a lot Oznog for the link!!!I had downloaded the data sheet before this,but had not thought in the direction you said in your post.

Okay,so I could use the sensor and get a voltage and then I could measure it and find out the realtive humidity.By the way,which IC should I use to get the relative voltage?

But there is one little problem after that.How do I connect a LED/LCD display so that the humidity is displayed on LED/LCD display?


Waiting for some posts.

Thanks.


:ranav::

 

[tanveerriaz]

you found dew sensors in old vcr ner by video head.
a white plate and black line on it.

 

[Oznog]

Plenty of PIC microcontroller chips out there which you can write code for to drive an LCD. Any of them can read a freq input. There are simple "multimeter" modules you can get out of a suplus catalog to read the analog RH module.

Really the PIC is the way to go. It's a substantial learning curve to get started, but they infer upon you essentially godlike power over almost any circuit project. This will serve you well for the rest of your career, far in excess of this one project.

 

[Oznog]

Plenty of PIC microcontroller chips out there which you can write code for to drive an LCD. Any of them can read a freq input. There are simple "multimeter" modules you can get out of a suplus catalog to read the analog RH module.

Really the PIC is the way to go. It's a substantial learning curve to get started, but they infer upon you essentially godlike power over almost any circuit project. This will serve you well for the rest of your career, far in excess of this one project.

 

[pranav81]

Thanks Oznog.

As you have successfully built this circuit,could you please send me the circuit diagram for the same?Or point to the website where I can get it?


:ranav::

 

[tanveerriaz]

Reading the SHT11 Humidity sensor
https://www.mcselec.com/an_116.htm

 

[pranav81]

Well....guys I have finally designed a circuit using the reference diagram from the Humrel data sheet.

I am uploading the circuit image so you guys can tell me some changes and the mistakes I have made.

See you soon.

:ranav::

 

[pranav81]

Well....guys I have finally designed a circuit using the reference diagram from the Humrel data sheet.

I am uploading the circuit image so you guys can tell me some changes and the mistakes I have made.

See you soon.

:ranav::

 

[pranav81]

Sorry.I uploaded the file twice by mistake.


:ranav::

 

[pranav81]

Hi guys.My professor has approved the circuit.The only problem I am now facing is regarding the sensor.The local stockist whom I asked if the sensor is available,now says that he wont order only one sensor for me.

So I would like to know some other sensors,that work on the capacitance principle as the Humirel one that I have used.It should approximately same specifications as the Humirel HS 1100/HS 1101 humidity sensor.I have already found 2 sensors from Gefran,on www.gefran.com and other
from Sensirion,at www.sensirion.com


Waiting for some positive repsonses.

Regards,


:ranav::