Light on Time
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My wife purcahsed this LED illumintaed sign and hung it in our small hallway.
She was very good at switching it on, but very forgetful re switching it off ! The obvious result being the fact we were changing the batteries far too often!
I decided the best solution to have it switch on by a sensor, but my main concern was drain on the batteries caused by the sensor.
Then I came across a 'little gem' PIR MH-SR602. It only draws 20 micro amps, (yes micro amps) while sensing and it has an adjustable 'on' time too!
Problem solved!
Component List
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MH-SR602 - eBay
100 uF capacitor (essential for stability an false trigger prevention !)
100 K timing resistor (this can be any value between 0 ohms & 316 M)
4.7K resistor
BC337 or pretty much any NPN transistor
About the MH-SR602
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There is some good information on the aliexpress site ...
https://www.aliexpress.com/item/32948972482.html?s...
The photo of the postion of the timing resistor is far better than my sketch!
I didnt bother with the sensitivity resistor, I actually removed it in error, nor did I bother with a photo resistor. I could not find much information pertaining to these 2 functions but I did not need them !
I did change the timing resistor.
****NOTE **** The table on the aliexpress site for the timing resistor is different to the one I used ! I'm not sure why it is different, but the 100K resistor I used gives me about 1 minute 'on' time !! ( Google MH-SR602 and look at 'images' !)
The default 'on' time is 2.5 seconds.
The 100uF capacitor is essential, as without it, all sorts of false triggering will occur!
The Circuit & Fitting
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The circuit itself it pretty straight forward.
When the MH-SR602 is triggered the output pin goes high for a duration dependant on the timing resistor and turns the transistor on, which in turn allows current to flow through the LEDs.
I removed the battery compartment and put the circuit between the negative battery wire and the battery connector. I drilled the bottom of the case and inserted the small circuit board.
Job done :-)