Hi,
Recently I bought cheap Chinese mini PIR sensor module and after few tests I noticed really short ON time just around 20s after trigger. After some reverse engineering and measuring I found out that changing value of RC oscillator changes time. Probably SO8 IC uses external clock source (originally set to 12kHz C 1nF, R 150k) red mark on pic.
Ok I thought to myself I solved problem but then I noticed that PIR module wasn't so sensitive anymore. I don't know why. I tried to tweak values of other R an C but with no significant differences.
So I decided to make my own circuit with PIR sensor. I hooked PIRs GND to GND, "drain" to Vcc and "source" (out) to BC547 via R 1k and 100k to the ground. Then I was watching signal on oscilloscope but I don't know why I only got noise and with my hand hovering directly over PIR I got few mV difference which is not enough for ADC of AVR microcontroller.
Now I have question if someone have any idea of simple PIR circuit without using op amp. I'm really tight on space on my PCB and I need simple but effective solution and because I don't have any experiences with PIR I'm asking for help.
Recently I bought cheap Chinese mini PIR sensor module and after few tests I noticed really short ON time just around 20s after trigger. After some reverse engineering and measuring I found out that changing value of RC oscillator changes time. Probably SO8 IC uses external clock source (originally set to 12kHz C 1nF, R 150k) red mark on pic.
Ok I thought to myself I solved problem but then I noticed that PIR module wasn't so sensitive anymore. I don't know why. I tried to tweak values of other R an C but with no significant differences.
So I decided to make my own circuit with PIR sensor. I hooked PIRs GND to GND, "drain" to Vcc and "source" (out) to BC547 via R 1k and 100k to the ground. Then I was watching signal on oscilloscope but I don't know why I only got noise and with my hand hovering directly over PIR I got few mV difference which is not enough for ADC of AVR microcontroller.
Now I have question if someone have any idea of simple PIR circuit without using op amp. I'm really tight on space on my PCB and I need simple but effective solution and because I don't have any experiences with PIR I'm asking for help.
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