# Motion Sensor Design

I'm trying to design a motion sensor alarm. If there is movement in my house, the motion sensor will send out a signal which will be connected to an alarm that will make a loud noise. I'm currently trying to pick the right motion sensor(ZRE200GE) and I found this https://www.zilog.com/docs/PS0336.pdf.

The output signal is described as Measurement Amp.: Non-inverted type, gain 72.5 dB at 1 Hz, 0.4 to 2.7 Hz／-3 dB

I'm really not familiar with DB stuff. But a google search showed me that 72.5db is equivalent to 4216.96 Voltage ratio which is something I'm very skeptical about (Too high of a gain). Is this conversion correct? Here is the recommended circuit from the sensor datasheet:

Here's what I have so far. My gain is 2 which should give an output voltage of 10V if I power the sensor by 5V, and my cutoff frequency is 1Hz. Here V1 is the sensor that outputs 5V like a sensor. Is there any fault in my design?

Note: This design is based on the assumption that when there is movement, the sensor turns on the FET which will connect the Drain and Source, hence opamp would also get 5V(roughly, of course, ignoring voltage drop across FET).

• Is there a reason you don't want to use pre engineered sensors?
– K H
Mar 21, 2021 at 7:40
• Cost and I want to do this way. Home project kinda thing. Mar 21, 2021 at 7:57
• Proper link: zilog.com/docs/ps0336.pdf Mar 21, 2021 at 11:12
• PIR sensitivity very depends on quality of lenses. Your own design may cost you mach more then to buy one ready to use. Mar 21, 2021 at 11:58

The high gain is correct.

PIR sensors show a signal of 0.5 mV under the best conditions. Under the worst condition the signal is 0.01 mV roughly.

I actually don't know what you got in mind but, if you want to simulate the amplifier circuit, I suggest you to start from Zilog's circuit.

Texas Instruments has a very good application note on PIR sensors' circuits because they sell low power operational amplifiers designed for PIR sensors.

Murata has a good application note as well.

In the past I worked with this kind of sensors and I noticed that all front-end amplifier circuits are pretty much the same.

Easiest way is buy from aliexpress a small size motion sensor(about 1.5 $) which needs ac 220 v. Fix the out put to a phone charger to get 5 v out put. Go to a motor bicycle parts shop and buy signal horn (1$)and fix it. I have fixed 3 of them around my house. I did by signal horn from alli at very low price.(1/2 \$).Mr Andyka's link says we can't diy it. Will take months. Please tell us if you finished it.Good luck.! When you finish it, difficalt to install, because dogs and bats will ring it. I have limited its eye and covered top,and placed on car hood so no dogs will ring it. https://i.sstatic.net/wTPm0.jpg)