help: Need 2 slightly Different Circuits for a Motion detector type alarm, prolly would take any expert 30 sec to make

[acidvoodoo]

i hope this is the right forum to post this. Basicly, this is for my high school electronics class. The project, which i will spend the rest of the year on, is to research, design, evalute an electronic product, and i chose a motion detector (very simple)

So we use a computer program to simulate circuits called crocodile clips, and print off 4 and choose the best one. So i came up with 2, and have chosen the best one already, just that for that part of the project to get marks, i need 4, and am really stumped, as i'm unsure how to make them slightly different. The circuit i am using basicly uses a push switch to emulate a vibration switch (there isn't one in croc clips), and when the alarm senses vibration, it triggers the alarm and does this for a period of time using a capacitor, and in my other circuit it uses a 555 timer thing.

So i'm stuck as to what else to do. If anyone can help me, remember the circuit does not have to be perfect, infact, deficienies would be good for me to write about.

If you use a different program to croc clips, then maybe you can take a screen shot of your program and print it and cut it out?

and if anyone knows websites that would help me, great


thanks for any help (oh, and if you have any ciruits for me, email them to below)

 

[Shalmanese]

Hmm... How bout getting a small PV cell and then using something to measure the voltage. When the light level drops below a certain level, it sounds an alarm. If you want to be a bit more sophisticated, measure the rate of change of the light level so it doesn't get triggered by the sun. If you want to make it directional, put a tube around the cell and point it to something like the door.

 

[blahblah99]

There are all sorts of motion detector circuits ranging: infrared, ultrasonic, light, proximity, shock/vibration, and heat.

They are all based on the same circuit theory - a comparator's input is referenced to a certain voltage (adjustable by a potentiometer to allow for sensitivity adjustment) while the other input to the comparator (with some hysteresis) is attached to the detector via additional circuitry.

When the detector "detects" changes, whether that is light, shock, or heat, depending on what kind of sensor you use, its output voltage changes. You figure out what the range of voltages are, and set your comparator's reference voltage level to the center of that range. Add some hysteresis to input on the detector side so the output doesn't jump around. Look at the datasheet for the LM393. It gives you example circuits and explains pretty much everything.

 

[capybara]

ok, instead of initializing the alarm by an input (hitting the switch)
why not instead initializing the alarm by a normally closed switch, which initializes when opened.
in real life, this is how windows and dows are alarmed .