Motion sensor

**Gogeta007** · Dec4-09, 02:39 PM

Im not sure if this should go here, but. . .
Im building a motion detector.

I have the breadboard hooked up the following way
using an op amp, a potentiometer, photocells, resistor and led.

After placing the Op Amp on the breadboard, put one pin on a Cds cell in the node connected to pin two of the op amp and the other Cds pin in the seventh pin of the op amp. The other cds cell likewise connects to pins two and four of the op amp.
Connect the middle pin of the potentiometer to pin three of the op amp, the right pin of the pot. to pin seven of the op amp and the left pin of the pot. to pin four of the op amp.
Connect the negative of the battery to pin 4 of the op amp
Connect the negative (usually shorter) lead of the LED to pin six of the op amp. Connect the other pin of the LED the 1K resistor. The other side of the 1K resistor should be connected to pin seven of the op amp.
Connect the positive battery wire to pin seven of the op amp.

http://img6.imageshack.us/i/breadboard.jpg/

So it seems to work fine, but I wanted to replace the LED with a relay switch, I was reading that you need a transistor to go with it to make a working switch. and I dont really know where to put the transistor, im guessing its between the op amp and the relay switch?

The question is:
How much voltage can go troug the relay?

Im making a discharge from 5 capacitors (330V around 100uF) as soon as the photocell senses movement, what I want to know is how to wire it.

heres my tought in a little drawing:

http://img207.imageshack.us/i/relayswitch.jpg/

or if anyone can tell me how to make one?
also if someone can recomend a sensitive motion detector (i want it to sense a small projectile thats supposed to be moving fast, but it should pass right by the photocells

==thnkz in advance==

-gogeta

**vk6kro** · Dec4-09, 06:48 PM

If the projectile is moving quickly, you would need to use a phototransistor as your sensor, as CdS cells are very slow.

You would also need to trigger a monostable to generate a long delay from the brief one caused by the moving projectile if you wanted to operate a relay. Relays are comparatively slow too, and yours would need a sustained pulse to pull it in.

Setting up phototransistors and monostables is not difficult, but it does require some experience to get it all working properly.

**Gogeta007** · Dec4-09, 11:56 PM

Originally Posted by vk6kro

If the projectile is moving quickly, you would need to use a phototransistor as your sensor, as CdS cells are very slow.

You would also need to trigger a monostable to generate a long delay from the brief one caused by the moving projectile if you wanted to operate a relay. Relays are comparatively slow too, and yours would need a sustained pulse to pull it in.

Setting up phototransistors and monostables is not difficult, but it does require some experience to get it all working properly.

i have some soldering experience and little breadboard knowledge.
Ive done a failing railgun and a successful single stage coil gun before
if its not too hard would you mind giving me some tips/list/directions?

anyways can the relay hold 330V as shown in the picture or will it fry?

**mabs239** · Dec5-09, 12:13 AM

Can you post the sensor circuit diagram here?

**Gogeta007** · Dec6-09, 03:06 AM

Originally Posted by mabs239

Can you post the sensor circuit diagram here?

I dont really know how to symbolize an op amp. so i did what i could

http://img260.imageshack.us/img260/7609/circuit.jpg

As I mentioned, it works fine (when it comes to making the LED blink)
but I want to know how to change that LED for a 330V switch

**mabs239** · Dec6-09, 04:40 AM

Here the LED is connected between op-ampoutput and +Ve terminal. I expected it to be connected with -Ve terminal.

So the LED blinks when opamp output is low. You may use any of following the two circuits.

http://www.rentron.com/images/NPN-DRIVER1.GIF
http://www.rentron.com/images/PNP-DRIVER1.GIF

Also please go through the following document to understand relays.
http://www.jaycar.com.au/images_uploaded/relaydrv.pdf