Using Relay Module

Question

Can I use a relay module to switch on & off a door alarm (1.5 V × 3)? Basically, can a relay switch work in this low DC power?

Also, I'm trying to make an alarm system which emits high noise when a particular set of sensors are triggered, so what I have done is that I have salvaged an old door alarm which will emit the sound and in order to do so I have to switch it on or off as per the sensor.

So, I am thinking of using relays; or if you can suggest any better option you are most welcome.

EDIT:

1. I'm using Arduino for the sensors & programming related to triggering the alarm & the alarm that I have salvaged is this one.

2. The Arduino and the Alarm are independently powered.

3. Since the alarm is independently powered by 1.5v * 3 batteries, can I use Relay just to switch on & off it via the Arduino? As all the videos & articles about relay are dealing with high voltage mains power, switching bulbs, fans etc can Relay handle low power/volt?

Answer 1

Some good info here, but let's keep this simple, yeah!? First off, yes, the relays can switch small DC voltages and small currents. You can purchase any number of "Arduino Relay Modules" that already have circuitry built into the module so you don't have to worry about flyback diodes and whatnot. Here are some links:

• Amazon
• eBay
• Sparkfun
• Banggod

All of these relay modules will work fantastic with just a 5V output from any pin on an Arduino. They all can switch any voltage from 0V up to ~120/240VAC, so you can switch the 4.5VDC you wish with ease. Another method to switch your alarm on without using a clunky relay is to use a NPN transistor as a switch. I won't explain how as there are many tutorials on it, but here's a great one if you're interested in that route:

• Easy tutorial
• In-depth tutorial

Answer 2

A relay would be fine, pick one that has low coil current if driving the coil from an Arduino, like this one.

Connect the coil+ to 5V, and the coil- to an Arduino pin, output a low to energize the coil. Put a diode like 1N4148 across the coil connections - anode to the Arduino pin, cathode to +5. That will protect the Arduino pin when the pin goes from low to high and the coil creates some current as it turns off, which will then dissipate harmlessly back into the 5V line.

Answer 3

Yes, pretty much any relay will work. It's better if it has not already been used to switch relatively high power.

Your question mentions a relay module, which is different from a bare relay. You should refer to the instructions that come with the relay module if you use a relay mounted on a PCB with optoisolator and/or drive transistor, LED etc.

To switch a bare relay directly with an Arduino you can use a circuit such as this (assumes +V is 5V):

^{simulate this circuit – Schematic created using CircuitLab}

Answer 4

1. Working of the relay at the mentioned voltage depends on the type of relay module you are using. Just try & see if the relay makes a "click" sound when connected to your power supply.
2. If your alarm is powered by mains voltage or is at a different voltage potential then you are bound to use a relay (a triac is also suitable) in order to turn it on/off.
3. Do not use a relay if you want to turn the alarm on/off rapidly. Since relay is a mechanical switch and may wear out easily when used in this type of scenario.

After the edit in your question:

A relay is just a mechanical switch. It does not matter if you are using it with mains voltage or in your case with (1.5*3=4.5v).

Answer 5

A simple transistor like BC637 can work for your application.