Touch Pad Sensor

[dashboyd]

Hi, I am currently doing a stress meter(bio medical project).In this project i have to use touch pad to detect stress level from our body.The touch pad using a finger tip to check stress level.Since i'm new to project environment,i cannot find where to buy this touch pad.Can you suggest any touch pad that suitable for this project and some websites that sells touch pad?Or can you tell places that sell touch pad in klang valley?

[yonghui]

hello,

u may wan to try this, force sensitive resistance:
http://cytron.com.my/viewProduct.php?pcode=SN-FRC-0.5&name=Force%20Sensitive%20Resistor%200.5%20Inches

i think it will be quite simple interface, will only need ADC to read from the voltage divider form by the sensor.


regards,
yh

[dashboyd]

Hi,Yonghui.Thanks for your info.
Is it the force sensitive resistance that you recommend can be used as a touch pad in the circuit of following website ?

http://dmohankumar.files.wordpress.com/ ... -meter.pdf

[yonghui]

hello,


i m not interested to read the whole document. but from the 1st few paragraph, i see that the circuit measure the skin resistance. from my guess the touch pad is just as simple as 2 conductive metal plate. the resistance in skin determine the small current through the base of the BJT transistor. this cause slightly larger changes of the current in collector or emitter of the BJT. current fluctuations in emitter cause the voltage across the emitter resistor to change and the IC shud be an opamp?that compare the voltage with standard calibrated reference voltage; then decoded by the ic and displayed by the LED for the voltage level.

if u are measuring physical finger press that cause the stress, then the sensor i recommended can be used.
else if u are measuring skin resistance, the sensor cannot be used.

of course the circuit given in the document still can be used for both case but with some calibration of the resistor value.


regards,
yh

[dashboyd]

Hello,
Based on your view about this project, i am measuring the skin resistance.So what sensor/touch pad you can suggest to me?And where i can buy the sensor/touch pad ?

[yonghui]

hi,

can u pls find out the explain to me the theory behind how skin resistivity is affect by human feeling of stress? i think factor such as the moisture of the skin after taking bath or weather can also affect the resistivity of the skin? how to compensate this? can u try to find out?

or u can try to do some measurement of the skin resistivity with the multimeter 1st and get some sample? set the dial to mega ohm range.

im not sure. but touch pad in the document i think is just two simple metal plate, nothing special. u can try to build up the circuit 1st and replace the sensor with some variable resistor series with megaohms resistor. try to adjust the variable resistor as replacement to the touch pad and skin.

regards,
yh