• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Help with simple circuit, motion on LED w/ auto off

JB123

New Member
Hi can anybody suggest the smallest possible configuration for a 5mm LED to light after motion detected within 18" and auto off after 90-120 seconds? Smallest battery etc. - Thank you! new to this.
 

AnalogKid

Well-Known Member
Most Helpful Member
Panasonic makes pretty small PIR sensors. After that, uC (microcontroller) will be the smallest, cheapest, and lowest power timer/logic circuit - IF you already know how to write code and program one. Of course it can be done with discrete logic chips, but even with sufrace mount parts it will be larger than a uC solution.

There probably are small motion sensor modules on ebay, maybe as an Arduino shield.

ak
 

billybob

Active Member
Panasonic makes pretty small PIR sensors. After that, uC (microcontroller) will be the smallest, cheapest, and lowest power timer/logic circuit - IF you already know how to write code and program one. Of course it can be done with discrete logic chips, but even with sufrace mount parts it will be larger than a uC solution.

There probably are small motion sensor modules on ebay, maybe as an Arduino shield.

ak
As AnalogKid mentioned, a nockoff arduino micro and maybe a small ultrasonic sensor would be the least possible parts, and probably the easiest.
 

AnalogKid

Well-Known Member
Most Helpful Member
I was think more like an 8-pin PIC as the sensor interface, timer, LED driver - everything. For a range limited to 18", a better sensor might be ultrasonic. However, the low-cost modules on ebay are larger than a simple PIR sensor. Don't know about how hungry they are.

ak
 

billybob

Active Member
I was think more like an 8-pin PIC as the sensor interface, timer, LED driver - everything. For a range limited to 18", a better sensor might be ultrasonic. However, the low-cost modules on ebay are larger than a simple PIR sensor. Don't know about how hungry they are.

ak
Ah gotcha.
 

gophert

Well-Known Member
Most Helpful Member
The ultrasonic sensors need about 180-250mA when running. You can pulse them with a microcontroller to take one measurement every 0.5 sec. or 1 sec to extend battery life by 20 to 40x but you'll need a PNP or p-channel mosfet to cut power to the ultrasonic sensor between measurements. I don't think PIR is any less power hungry. Sensing large arenas gets energy intensive. I don't know if a short range (18-24") PIR sensor exists. Most modules I've seen are higher power snd longer range to sense my back yard, entry door, etc.
 

Latest threads

EE World Online Articles

Loading
Top