How to connect sensor to PC?

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Thread Starter

Shen

Hi there,

I am an engineering student. I am currently doing a project which used PIR sensor (Pyroelectric infrared sensor). I do hope to ask some questions. This sensor detects body heat and produce some voltage.Somehow, the voltage
wouldn't remain 5V when it detected movement. So I would like to know how to maintain the circuit output to TTL level signal(2.4 to 5V)so i can connect it to the parallel port then to PC. I am new to this subject, so i am really desperate for help. You can reply me through
"[email protected]", mailto:[email protected] . Thanks a lot!

Regards,
Shen
 
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Dr.V.G.Anguraj.

dear shen,
In your case, please check the NPN or PNP Transistor sensor, if it is in NPN means, it will come (NC) supply voltage to the o/p.
Otherwise please add the voltage regulator (Using transistor and zener diode) circuit in your o/p of the sensor.
how are you connecting to pc?. Either you are using any PLC or controller circuit?
bye
 
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Peter Whalley

Hi Shen,

PIR detectors look for variations in signal level from the detector as a warm object moves in and out of it's detection zones. In very basic terms you would AC couple the signal (using a high pass filter with a very low cut off frequency - say 0.1 of a Hz) to eliminate the DC component which relates to average room temperature, then rectify the AC signal and feed it into a Schmidt trigger to convert the analogue signal to TTL. You may also want to go through a pulse counter before feeding the signal to the PC (or do this in the PC) to reduce false alarms.

Modern professional PIR movement detectors use quite complex signal processing to eliminate false alarms and improve sensitivity. This is often incorporated into a custom designed ASIC but the above is the general principle.

Regards

Peter Whalley
Magenta Communications Pty Ltd
Melbourne, VIC, Australia
e-mail: peter*no-spam*@magentacomm.com.au
delete *no-spam* before sending
 
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