First Post - Looking for a motion sensor circuit to cover a hole.

First Post. Nice Site.
There is a lot of smart people and usefull knowledge here I have noticed.

I have been looking on here but can't find all the answers, So I figure I would put up a post.

Im looking for a circuit diagram or any help. I have a little bit of electronics knowledge.
Im looking to make a sensor circuit to cover a 6-7" round hole and set off a buzzer for a second or two then reset.

Something that can run on a 6 volt battery. Something that will not be set off by vibration/bang. Needs to go off with a non heat item. Such as a 2" or so material item passing thru it.

From what I have noticed it looks like a PIR will not work becaust it goes off with heat. Beam sensor seems to be to narrow.
I was looking at some light sensors but not sure if they would work correctly being used at night and then into sunlight with the same settings.
Thanks in advance for any help.

You could use several light emitters/sensors with the beams spaced less than 2" apart. Actually a single wide angle emitter with several sensors would probably work.

To minimize the effect of ambient light you can square-wave modulate the beam (rapidly turn on and off) and use an ac amp to detect the signal. You just have to prevent direct sunlight from saturating the detector. Also use an IR LED source and a detector filter to suppress ambient light (a dark red filter such as used in remote controls). A remote control detector module which is designed to detect an AC signal such as RadioShack.com - Cables, Parts & Connectors: Component parts: Transistors & analog ICs: 38kHz Infrared (IR) Receiver Module or TSOP1156KSI IR Receiver Module (Pkg of 3)-The Electronic Goldmine should work.

Any links to circuits? For me to create without I would be clueless.
Sunlight would only shine thru the hole from the top. Everything would be mounted on the bottom at least 1" or more from the hole. Not sure how that would play on the sensors with the sun shining thru.
Thanks

crutschow said:

You could use several light emitters/sensors with the beams spaced less than 2" apart. Actually a single wide angle emitter with several sensors would probably work.

To minimize the effect of ambient light you can square-wave modulate the beam (rapidly turn on and off) and use an ac amp to detect the signal. You just have to prevent direct sunlight from saturating the detector. Also use an IR LED source and a detector filter to suppress ambient light (a dark red filter such as used in remote controls). A remote control detector module which is designed to detect an AC signal such as RadioShack.com - Cables, Parts & Connectors: Component parts: Transistors & analog ICs: 38kHz Infrared (IR) Receiver Module or TSOP1156KSI IR Receiver Module (Pkg of 3)-The Electronic Goldmine should work.

Click to expand...

Anyone Else with ideas?

TV-remote controls are not sensitive to heat. You could use an NE555 oscillating at 38KHz and and a receiver TSOP38838, either operated as an IR-barrier or reflective barrier.

The reflective barrier requires high transmitting power (>100mW/sr) and therefor I don't recommend that for battery operation. The barrier requires one IR-TX-LED, e.g. LD271 (15mW/sr) or LD274 (>50mW/sr) depending on the range.

Boncuk