# Building a Motion Detector with Relay Switch and Capacitors

• Gogeta007
In summary, the author is building a motion detector. He has the breadboard set up in the following way: an op amp, a potentiometer, photocells, resistor and LED. After placing the op amp on the breadboard, he connects one Cds cell in the node connected to pin two of the op amp and the other Cds cell in the seventh pin of the op amp. The other cds cell likewise connects to pins two and four of the op amp. Next, he connects 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.
Gogeta007
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.

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 don't really know where to put the transistor, I am 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/img207/8531/relayswitch.jpg

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

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

-gogeta

Last edited by a moderator:
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.

vk6kro said:
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?

Can you post the sensor circuit diagram here?

mabs239 said:
Can you post the sensor circuit diagram here?

I don't really know how to symbolize an op amp. so i did what i could

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

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

Last edited by a moderator:
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.

Last edited by a moderator:

## 1. How does a motion detector with relay switch and capacitors work?

A motion detector with relay switch and capacitors works by utilizing the principles of motion detection and electrical circuits. The detector uses a sensor, such as a PIR (passive infrared) sensor, to detect changes in infrared radiation caused by movement. This sensor then triggers a relay switch, which allows the flow of electricity through the circuit, activating the connected device. Capacitors are used in the circuit to store and release electrical charge, helping to regulate the flow of electricity.

## 2. What materials are needed to build a motion detector with relay switch and capacitors?

To build a motion detector with relay switch and capacitors, you will need a PIR sensor, a relay switch, capacitors, resistors, a power source, and wires for connecting the components. You may also need a breadboard or PCB (printed circuit board) for assembling the circuit. Additionally, you will need basic tools such as a soldering iron and wire cutters.

## 3. Can a motion detector with relay switch and capacitors be used for home security?

Yes, a motion detector with relay switch and capacitors can be used for home security. By connecting the detector to a security system or an alarm, it can be used to detect and alert for any movement in the monitored area. However, it is important to note that a motion detector with relay switch and capacitors may not be as reliable as professional security systems and should not be solely relied upon for home security.

## 4. What are the advantages of using capacitors in a motion detector with relay switch?

Capacitors help to regulate the flow of electricity in a motion detector with relay switch, making the circuit more stable and efficient. They also help to filter out any unwanted noise or interference in the circuit, improving the accuracy of the motion detection. Additionally, capacitors can store and release electrical charge, making them useful for applications where a sudden surge of power is needed, such as when triggering the relay switch.

## 5. Are there any safety precautions to consider when building a motion detector with relay switch and capacitors?

As with any electrical project, it is important to take proper safety precautions when building a motion detector with relay switch and capacitors. Make sure to disconnect all power sources before working on the circuit and use insulated tools to avoid electric shocks. It is also important to double-check all connections and components before powering on the circuit. If you are unsure about any step in the process, seek guidance from a professional or do further research to ensure safety.

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