What circuit makes a HIGH by detecting LAST pulse

[Minu]

Hi,
I am using a PIR sensor in my project for human presence detection( not to detect human motion). As you know, PIR sensor is for human body MOTION detection. In market, human body detection sensors are there. But all that are costly. As a low cost sensor, i chose PIR motion sensor.

My doubt is how can i use a PIR motion sensor to detect the presence of a human? In my project a person will be always sitting infront of the sensor. But he defenitely move. So there are number of HIGH pulses coming at the output of PIR sensor. I need a single HIGH output as long as the person is sitting infront of the sensor. When he leave the chair, the output have to become LOW after a time period, to wait for any pulse signal from PIR.

I Wish to do my project only by using circuit. Dont want to use any kind of programming.

Is there any circuit which continuesly monitor high pulse inputs and provides a HIGH dc output. Also the output have to maintain HIGH level for a time period after the LAST pulse input.

Kindly reply asap

 

[Minder]

A watchdog timer type of operation using say a 555, if you want a delay after last pulse then either another 555 time out or a 556 double 555.
M.

 

[Alec_t]

A re-triggerable monostable circuit should do the job.

 

[Minu]

Thank you sir..

 

[Minu]

I couldn't understand what exactly u mean. Could u plz explain it?
Thank you for ur kind reply

 

[Minder]

Essentially what the 555 does.
http://www.falstad.com/circuit/e-555missing.html
Click the L to H.
Plenty via Google
555 Missing pulse detector.
M.

 

[Minder]

This show it a little clearer, if the input is pulsing the output stays low, once the pulses stop the output changes.
http://www.falstad.com/circuit/e-555monostable.html
M.

 

[Minu]

Thank you sir.

 

[HellasTechn]

A watchdog timer type of operation using say a 555, if you want a delay after last pulse then either another 555 time out or a 556 double 555.
M.

A re-triggerable monostable circuit should do the job.

It is called "Missing Pulse Detector" and it is with a 555 timer.

This show it a little clearer, if the input is pulsing the output stays low, once the pulses stop the output changes.
http://www.falstad.com/circuit/e-555monostable.html
M.

only with +5v VCC you are very close to the minimum 4.5V that the 555 can run with. I suggest a +6V or +12V VCC.

 

[Bluejets]

Elcheapo sensors from Ebay are around $15 so I would not call that expensive.
No need to add anything to the sensor as in your application.
you require the sensor to retrigger with every movement so set pir timer to say 20 minutes and it will retrigger with every movement and keep out put high. You will not see the effect of each retrigger and after the time out the output will revert to low if no further movement is detected. Timing restarts after every retrigger.

 

[Minu]

Ya..thanku sir

 

[Minu]

I think you are saying about the timer which is programmed in adruino or such controllers. Is that so? I actually planned to use only circuit components, with out using any kind of programming..i wish to make it as cheaper as possible.
Thank you for your kind reply..

 

[Bluejets]

No...read my post.

As an example here is a 12 v unit,

220v mains units also available.

https://www.ebay.com.au
10-50w-12v-Outdoor-Security-PIR

 

[Minder]

It is called "Missing Pulse Detector" .

AKA Watch-dog timer..


Every PC has one.
https://www.microcontrollertips.com/whats-watch-dog-timer-wdt/
M.

 

[HellasTechn]

AKA Watch-dog timer..

The watch-dog timer is different than an lm555 missing pulse detector but in this case both can do the same job.

I like the 555 missing pulse detector more Plus it requires no programming (not sure about the watch-dog timer) and is so so easy to make.

 

[Minder]

Just two names for the same function!
Watch dog timer can be made from 555, no programming.
http://upperbound.com/projects/555-watchdog-timer/
M.

 

[(*steve*)]

A resistor to ground will do this for you.

My reasoning is that you never know when the last pulse is going to come, so the output simply needs to stay low.

I did consider the death of the universe as a triggering event for the output going high. Even ignoring the difficulty of detecting this, any propagation delay means the rising edge wont begin until after the end of the universe, so the simple pull down is still equally effective.

:-^