hi, iv got to do a project for my electronics course, so i thought id make a mouse trap, using an infrared beam to trigger the door closing mechanism.

it will be a long tube, with the beam at the back, and a trap door at the front held up by an electro-magnet which will be triggered on by a switch, and off by the IR beam being broken (hopefully by a mouse). Is there anyway i can make it for only mice and not just anything like a spider that decides to go inside?

also, the electronics i took from this site:

http://www.ee.washington.edu/consele...inal/final.htm

ill have to power this from 2 6volt batteries i think unless someone can think of a more cost effective way?
what i really want to know is, will the output be able to power an electro-magnet and an LED? and also if anyone could tell me how many windings on a piece of iron would i need for a decent magnet? like 300? and does it matter which possition the windings are in or just in middle will do?

thnx a lot for any help

 

use two sensors, spaced so only a large (realitively) object can trigger the door. this way you'll only catch rodents or really big spiders!

this setup should run fine off one six volt battery ... I guess it all depends how long you want it to run for.

think of some sort of catch mechanism to hold your door open rather than wasting power continously on a magnet. then you only need a short burst from a magnet to release the catch

 

thnx for help

hmm, if i was to use 2 sensors... wouldnt i need to duplicate that setup, thats a lot of components :-\

oh thats cool then, what if i was to use 4x1.5v batteries connected together. then they could be rechargable

ok, if i have a small metal bar through the door holding it up, then a the magnet turning on to pull it back droping the door, but then turning off again... im not sure how i would turn the magnet off again. ill have a think about that, thnx a lot

 

Requiring the electromagnet to operate continuously to keep the door up is a bad idea. If the door were spring loaded, and there was a small lip that it would rest on to keep it up, then the electromagnet could pull the door off of the lip allowing it to slide down into the closed position. You would probably have to briefly pulse the magnet to pull it off the lip, then turn it off so the door could fall.

Dan East

 

well, if you use ir emitter detector pairs, and wire the detectors in series, aka an AND gate, that really doesn't require any extra parts

the only thing that's going to take a lot of power is the electromagnet, and properly designed, only briefly ... three or four 1.2v rechargables should be sufficient for the logic side of your circuit.

 

thnx for the help, its really appreciated

hmm, do u mean just buy 2 IR photodiodes and 2 IR phototransistors? or is there a sort of package...

also when wiring them using an AND gate, theres 2 inputs and 1 output, so would i put the 2 diodes after the .220 resistor and put each diode into each input of the AND gate then ground on the output? im really not sure on this part sorry, it makes sense, but i dont know how to use it.

btw, can i just connect the 4x1.2v batteries to both circuits, or will i need 4 for each circuit?

thnx

 

this is for your school, so it wouldn't be right of me to help you with the research

here's some info on diode logic (which is used to build AND / OR gates) ... the first few links are great

http://www.google.com/search?q=diode+logic

by pair, I just mean one emitter, one detector ... what package they are in, separate or together, is entirely up to you.

 

well thats for normal diodes, im not sure if the same rules apply to IR diodes. if they do, i just connect them reversed one after the other and put a 4.7k resistor before the ground? because in the 3rd links diagram, it has a seperate powersupply and routes A and B. I assume these routes would be, in my case, from the timer, and i would get the power from that, so wouldnt need seperate, and also the 'ouput' in the diagram i would leave out so it would just be the 2 diodes reversed connected in series and an extra resistor then?

thnx

 

Regarding the magnet, look for a small solenoid which is an electromagnet mechanically set up to pull or push a lever. You may find one in a junked VCR, especially the older types.
To get it to operate just momentarily, connect the coil in series with a capacitor. Think about what happens to the current the instant a voltage is applied to the capacitor and what happens a few seconds later when its charged. You may need a large resistance across the capacitor to provide a slow discharge path so its ready for the next triggering.
Klaus

 

thnx for the tip but its for a project, and i really need to be able to say that i can produce the device relativly cheaply. I looked on maplin just now and they cost £12 to buy, and a company cant just go round scrapping vcrs for parts :P
so is there anyway i can achieve the same with a self-made electromagnet or will i have to buy one of these? (just a check: electromagnets consist of an iron bar with 300 or so windings of insulated wire wrapped round it in the middle yer??). Id have to build it so the system will stay on for a few seconds after the beams have been triggered, so the magnet has time to pull the bar back dropping the door, and then turn the whole system off..

on the first circuit, say i had a NAND gate connected with 1 input from the batterys (1.2V group) on the emitter circuit and the other input from a wire coming from after the first op-amp on the detector circuit. Then the first circuit will turn off if it detects something right? would that work?