LPG Gas Sensor Module (#27932)

[ladladlad]

Hi, i'm currently doing a project using LPG Gas Sensor Module (#27932) from parrallax and msp430.

http://www.parallax.com/Store/Senso...ortField/0/Level/a/ProductID/593/Default.aspx

i think i should give u guys some info that i know, TP 3 & 4 is the refrence voltage while TP 1 & 2 changes due to the concentration of the gas. That abt all that i know

i have encounter a few problem while i'm calibrating the gas sensor.

Firstly, i'm calibrating it without any micro-controller(because i dun have 1)(which might lead to my second problem)

Secondly, the voltage between TP 1 and TP 2 should increase when it detect related gas, but for me, it increases even without any gas. So is there anyway to stablize or keep the voltage low between these point.

Thirdly, my friend suggest me to use the attached circuit, i have tired it, the voltage still increases slowly over time, but after it goes pass the refrence voltage, it goes down to 0.016 volt, which is good, but i want it to stay like this when from the start, and not after so long.

sorry if i have confuse some of you with my english, but i really hope that you guys could help, thank in advance. cheers

 

[Harald Kapp]

The sensor uses a heated element. Heating takes some time. The manual (http://www.parallax.com/Portals/0/Downloads/docs/prod/sens/27904_27930-1-2-GasSensor-v2.2.pdf) states that you should wait at least 10 minutes before calibrating the sensor. This is the time the sensor needs to set into stable operation.

Harald

 

[ladladlad]

thx Harald.

i did try that before, and i still get the same result. The only thing i'm wondering now is if i realyi need to use the basic stamp module like what they say.Hopefully not as i dun have 1.

 

[Harald Kapp]

No, any microcontroller can do.

 

[ladladlad]

No, any microcontroller can do.

Ohhh. Ok. So I connect alr output to input of my micro-controller. What abt de Hsw. Do I need to connect it to my micro-controller too?

 

[Harald Kapp]

What do you mean by Hsw?

 

[CocaCola]

What do you mean by Hsw?

It's the heating element enable input...

ladladlad read the datasheet for the module, it explains exactly how you hook it up, and calibrate it...

Note that they say wait 10 minutes before taking readings and not that they state that temperature and humidity will effect calibration...

Yes, you need to hook up HSW to turn on the heating element or short it to ground to be always on... Adjust the settings as explained in the datasheet and monitor ALR, ALR will go HIGH once the trip threshold is breached... You adjust the trip threshold with the two pots as described in the datasheet...

And last but not least, no you do not need a micro to operate this it's simple digital logic, you can interface it to just about anything and/or any micro you choose... As I stated you can short the heater to ground to have in always on and then all you need to do is calibrate and monitor the ALR line for a high signal when it detects gas... Although I suspect if you short the heater to ground and run it 24/7 you might very well put it on a path of shortened life...

BTW the schematic you posted above makes no sense, and won't work... The heater has to be enabled for the sensor to take a reading yet in your schematic the heater won't be enabled until the sensor senses gas... You have the classic chicken before the egg issue... Whoever suggested you hook it up like that is either clueless, lost or didn't bother even reading the datasheet...

 

[ladladlad]

It's the heating element enable input...

ladladlad read the datasheet for the module, it explains exactly how you hook it up, and calibrate it...

Note that they say wait 10 minutes before taking readings and not that they state that temperature and humidity will effect calibration...

Yes, you need to hook up HSW to turn on the heating element or short it to ground to be always on... Adjust the settings as explained in the datasheet and monitor ALR, ALR will go HIGH once the trip threshold is breached... You adjust the trip threshold with the two pots as described in the datasheet...

And last but not least, no you do not need a micro to operate this it's simple digital logic, you can interface it to just about anything and/or any micro you choose... As I stated you can short the heater to ground to have in always on and then all you need to do is calibrate and monitor the ALR line for a high signal when it detects gas... Although I suspect if you short the heater to ground and run it 24/7 you might very well put it on a path of shortened life...

BTW the schematic you posted above makes no sense, and won't work... The heater has to be enabled for the sensor to take a reading yet in your schematic the heater won't be enabled until the sensor senses gas... You have the classic chicken before the egg issue... Whoever suggested you hook it up like that is either clueless, lost or didn't bother even reading the datasheet...

thanks for your clear explanation coca.

And yes, we were very lost when we got this gas sensor.

will try what u said tmr when i get back to the lab

btw, any other ways to turn on HSW, expect shorting it to the ground? and if a micro-controller can do it, can u give me a rough idea on what to do?

Hope this isn't too much to ask for

thanks in advance

 

[CocaCola]

btw, any other ways to turn on HSW, expect shorting it to the ground? and if a micro-controller can do it, can u give me a rough idea on what to do?

Instead of shorting it to ground you could pull it to ground with a resistor... As for how to do it with a micro, you hook HSW up to a digital i/o pin and tell the micro to take that pin low aka ground it...

 

[ladladlad]

Instead of shorting it to ground you could pull it to ground with a resistor... As for how to do it with a micro, you hook HSW up to a digital i/o pin and tell the micro to take that pin low aka ground it...

ohhh. ok. thanks will update you guys on my project progress

 

[CocaCola]

BTW I just looked at my reply, what I said applies to micros running at 5v, if you are running your micro at 3.3v micro you need to take the pin low using a transistor as outlined in the documentation for the sensor...

 

[ladladlad]

BTW I just looked at my reply, what I said applies to micros running at 5v, if you are running your micro at 3.3v micro you need to take the pin low using a transistor as outlined in the documentation for the sensor...

ohhhh. ok

tried out your method and it work perfectly

just wanna tell you guys abt my idea, i will try to use the TP 1 and 2 to be the input for my micro-controller, so that it will react due to the concentration of the gas.

when the voltage is low ( led light up)

when the voltage is in the middle ( buzzer start ringing)

when the voltage is high ( will send a sms to some1)

so, any comments about tis??

please excuse me for my poor english standard