Arduino + Relay Explanation

Hi there. I am very new to Arduino n Relays. Can somebody please explain me this diagram of Relay + Arduino

Solid State Relays will connect to Arduino the same way?

Solid State Relays will connect to Arduino the same way?

No a solid state relay will look to the Arduino like an LED.

Not a lot to explain, it shows a transistor driving the relay. The relay coil is the square with the line through it. The transistor is the symbol with three connectors labelled base, emitter, collector. R1 shows a resistor, and D1 is a diode. The dotted line shows the relay contacts that are switched.

thanks for the reply.

BTW which relay is safe to deal with AC high Voltage (120V)? Simple Relays or Solid State Relays?

They are both safe as long as you use them within their ratings. That is not push more current through them than they can stand.

A mechanical relay is disconnected when it it off where as a solid state relay is only powered down, so there is a tiny leakage current and you might get a tingle if you touch the powered off live wire, which you shouldn’t be doing anyway.

OK got it thanks.

One more thing, can i use these Relays to make a circuit on Breadboard? Can breadboard handle that much current?

You are not dealing with much current here. I wouldn’t use breadboard above 800mA though. The main problem is mechanically fixing it.

Ok right, so you wont recommend using breadboard for that much current (10Amps). Then what will be the best option to do the circuit? I have never done circuits without breadboards.

Then what will be the best option to do the circuit?

Solder it up on strip board and use wires for the interconnects that carry the large currents.

Alright i have got this relay, i think its a Solid State Relay, will it serve the purpose of powering up a Coffee maker or a simple Bulb that take 110V of current

Its specs show that its input is DC4[ch65374]7[ch65334] and Output is 20A \620.

I think arduino can output 5V so i can connect this to arduino to power it up, right??

I think arduino can output 5V so i can connect this to arduino to power it up, right??

Yep, an Arduion digital output pin will drive that directly. However one thing that many miss using these SS relays is that if you are going to be controlling a lot of AC amperage, possibly the amount that a coffee maker uses, then you might need to heat sink the device. Notice how the back side is flat metal, this is the heat sink surface designed to bolt to.

Lefty

thanks for the reply.

I have found a link having almost the same thing. The circuit in this example uses another 5V to power up, why is this so? Isnt this circuit is taking the power from Arduino? This guy is also using breadboard so I am a bit confused

http://www.glacialwanderer.com/hobbyrobotics/?p=9

The circuit in this example uses another 5V to power up, why is this so?

Because he is using a mechanical relay not the solid state relay that you have.

This guy is also using breadboard

The bread board is only for the low current stuff that drives the mechanical relay coil.

Quote:
The circuit in this example uses another 5V to power up, why is this so?

Because he is using a mechanical relay not the solid state relay that you have.

Quote:
This guy is also using breadboard

The bread board is only for the low current stuff that drives the mechanical relay coil.

Ok thats some good info, thanks.

Now i got to know these things

  1. Solid State Relays do not need to get connected like other relays, they just connect like an LED.

  2. SSR do not need an external power, they can get the power from Arduino pins.

  3. I should not use BreadBoard with high Current in case of SSR.

  4. SSR retains the current even after turned off.

Anything else i need to know about SSR before playing with AC high Voltage?

Anything else i need to know about SSR before playing with AC high Voltage?

Yes, they work best with resistive loads like lamps. With inductive loads like motors and solenoids they sometimes require external snubber components.

Lefty

Thanks for the replies guys.

BTW for this Circuit i have these following things, are they enough?

  1. SSR[ch12288]MITSUBISHI[ch12288]SF20DPS-H1-4 [ch12288]IN: DC4[ch65374]7[ch65334][ch12288]OUT: AC240V

  2. 1N4004 Diode → 1N4006 (1A 800V)

  3. 2N2222 Transistor

  4. 1K Resistor. (BTW which resistor will be best, i have got a bunch of resistors )

  • 1/4W Carbon:
  • 1/2W Carbon:
  • 1W Metal:
  • 2W Metal

Do i need something else to make this circuits?

  1. SSR retains the current even after turned off.

No I said that there is current leakage through a SSR when t is off. There is nothing retained like there is when a capacitor charges.

  1. 1N4004 Diode → 1N4006 (1A 800V)

  2. 2N2222 Transistor

  3. 1K Resistor. (BTW which resistor will be best, i have got a bunch of resistors )

What are you doing? You only need these with a mechanical relay.

Thanks for ur kind replies :slight_smile:

BTW dont i need any Resistor inbetween the Relay and GND of Arduino? Or can i connect the Arduino directly to Relay? Isnt it dangerous for Arduino?

Sorry for these noob questions, please bear with me

This is how i feel the circuit should look like

Yes that’s right.
The SSR has it’s own internal resistor.
The current requirement for the SSR is less than the maximum current you can get from a pin.

The diagram looks good, and the discussion is fine so far. Just a couple of extra clarifications:

  1. I’m not sure that ALL solid state relays have a built-in resistor on the LED side. Check the datasheet to be sure.
  2. you can use a breadboard on the “control” side of a high-current relay circuit, just not on the high-current “controlled” side.
  3. MANY solid state relays will control AC only. Since that’s what you want to do, you shouldn’t have a problem, but you can’t necessarily stick a 20A SSR into a circuit where you want to control 20A of DC current.