# How do I set the Pressure that triggers a QTC sensor?

Discussion in 'The Projects Forum' started by infrared, Jan 31, 2011.

1. ### infrared Thread Starter New Member

Apr 25, 2010
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0
Hey guys,

Just a simple question but I cant find the solution online as I dont really know what to search.

I am trying to make a circut where the user is always on the sensor but when they put more pressure on the QTC mat a simple buzzer is triggered.

Basically I just want to know how to set the sensitivity of a QTC sensor to be activated when 15kg is pushed down.

Is it a combination of resistors or potentiometer?

Thank you

Will

Last edited by a moderator: Feb 1, 2011
2. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
You are probably looking for a comparator circuit, depending on the output of the mat.

3. ### Adjuster Well-Known Member

Dec 26, 2010
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Is someone (the user) already standing on the mat before a further 15kg is added??? How much does the user weigh?

4. ### infrared Thread Starter New Member

Apr 25, 2010
9
0
The 15kg was an example, I have not yet measuerd the force. But in this example someone is standing on the mat. when they lean on one leg, more pressure is exhurted triggering the QTC.

Will

5. ### Adjuster Well-Known Member

Dec 26, 2010
2,147
300
First find out how much force is exerted, and use that to predict the mat response, or (much better) find out the mat resistance response by measuring that directly with a resistance meter. Get figures for no pressure, standing, and leaning. Are you sure that the extra pressure from leaning on one leg will produce a significant additional response?

Given an adequate resistance response, I would have thought that a Wheatstone Bridge circuit driving a comparator would be suitable. The mat would form one element of the bridge, and the other resistors would be chosen so that the bridge reaches balance at the appropriate pressure.