Low power sensors for detecting people

Projects General Guidance
1

Hi all,
Im working on a project for my 8 year old nieces that is an room alarm with keypad deactivation.
I have the keypad part working, but I'm trying to figure out what sensor to use to detect a person walking into the room.
I would like the device to be battery powered, so low power sensors are key. I'm thinking of putting the uC in sleep mode, then waking it up, say 10 times per second to help with the low power requirement.
As the children are young, I don't want to use lasers for obvious safety reasons.
I had been thinking of using IR LEDs but my research indicates that ambient light will likely interfere.

Does anyone have any suggestions?

2

There are some very low power PIR sensors that could wake up the microprocessor upon motion detection. Here is an example PIR (motion) sensor : ID 189 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits

3

rosscopicotrain:
Hi all,
Im working on a project for my 8 year old nieces that is an room alarm with keypad deactivation.
I have the keypad part working, but I'm trying to figure out what sensor to use to detect a person walking into the room.
I would like the device to be battery powered, so low power sensors are key. I'm thinking of putting the uC in sleep mode, then waking it up, say 10 times per second to help with the low power requirement.
As the children are young, I don't want to use lasers for obvious safety reasons.
I had been thinking of using IR LEDs but my research indicates that ambient light will likely interfere.

Does anyone have any suggestions?

  1. Pressure sensor(s) under the carpet.
  2. Microswitch or magnetic reed switch/Hall effect sensor on the door frame.
  3. Capacitive touch sensor on the door handle.
  4. Put your IR LED at the back end of a lightproof tube and your photo-transistor at the back end of a similar tube. Point the two tubes towards each other in a straight line, like two telescopes, to avoid any ambient light problems.
  5. Modulate the IR LED at a frequency that isn't a direct harmonic of your mains frequency and detect only that frequency.
4

PIRs - Passive InfraRed sensors - are the standard answer to your question.