hi all, i'v designed a 8x8 matrix which is controlled by a 16f876a displaying the the time from a ds1337 ic.The problem is i only want the display to turn on and display the time when some one is standing in front of it and if possible i want to be able to adjust the distance that turns it on. I have no idea on how to do any motion detection, should i be using i.r emitters and reciever or something else.

please can some one help me with the circuit and ill try and do the code for it.

many thanks
jason

 

search this site, there is bunch of threads related to this:
IR Distance Sensor
proximity detection
Advantages...
...

in short, you put IR diode and modulate it at 38 or 40KHz, you use IR receiver (same freq as the signal you are generating) just next to it, tune the power output of the IR diode to achieve right distance .. when you detect signal on IR receiver - you have someone in front of the device

 

i'm looking for ranges from 1 to 2 meters so would i be better using ultrasonic

 

Use a PIR detector. That way you don't need a separate TX and RX.

 

pir is a great idea if you can find one that will work in your environment. I experimented with couple of different pir sensors and abandoned the idea completely for all projects as they just trigger to often on too many "non triggerable" events.

IR might be made sensitive enough (tx powerful enough) to get 1-2m without too much troubles (add few leds in parallel and drive them with max rated current, you will get much more then 2m, much much more)

ultrasound is great thing, I tried to play with it some time ago but wasn't able to finish the project as pressure on job increased so free time got vaporised .. but you can find some nice ultrasound schematics on this forum and some nice pointers from few other "really smart ppl"
In any case, doing it with ultrasound will take
- TX capsule (not cheep)
- RX capsule (not cheep)
- demodulator circuit (amplifier, demodulator, all analog - not my area really )
with compared to IR one where you need few transistors to drive led's and one ir receiver that does everything for you (amplification, demodulation) the price for IR one is ~10x lower then for the US one .... also, IR is much easier to focus the sound

 

Maxbotix ultrasonic sensors are excellent. They're reasonably priced, very simple to interface (multiple interface methods on every sensor - you choose what works for your project) and accurate.

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Futz's Microcontrollers & Robotics
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My PIR sensor doesn't give false alarms ever. They're everywhere, so they have to be reliable.

 

You can buy a real good pir from radio shack for 10 dollars that would work good
it's made by parallax it has a jumper on it that changes it's out put from being
high or low to where you can count the pluses and tell how far away things are thay have code for the stamp. I been playing with it with my scope. Trying to think of a way to use it with a 12f675 on a little bot I made