Most of the Arduino runs on 5V and driving low power actuators like LED is fine with a resistor but how do I control relays / motors / pump / fans that runs more than 5V ?
I get a lot of beginner questions like below :-
1. How do I switch ON & OFF a 12V DC fan from an Arduino ?
I was told I need a relay, what type of relay should I get ?
2. How do I control the speed of a 12V DC motor or fan from Arduino ?
Let's look at these scenarios one by one so that I can explain them in more details. Firstly, even if a motor or pump or fan (anything with coils inside) is 3V or 5V, do NOT power it directly from the Arduino pins as the Arduino pins can only supply a maximum of 40mA. As per my previous article on Arduino pins, they are not designed to drive a DC motor or coils.
Always use a separate power source to drive these high load components and have a relay to switch them.
Question 1:-
How do I switch ON & OFF a 12V DC fan from an Arduino ?
How do I switch ON & OFF a 12V DC fan from an Arduino ?
I was told I need a relay, what type of relay should I get ?
A 12V DC fan or motor have coils inside it. You would need a relay to control it. A relay is an electrically operated switch to turn on or off a device. Most relay use an electromagnet to operate a switching mechanism mechanically. You could hear a "click" when the relay switches on when it magnetize the coil and turn on the switch. Below is an image of a 12V Single Pole Double Throw (SPDT) relay housed in a transparent casing. You can see the copper wires winding or coil clearly.
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| 12V SPDT relay |
The advantage of a relay is that they can allow high flow of current and voltage across them but the disadvantage of a relays is that it is a mechanical device with springs, so the switching speed is much slower than semiconductors ( called switching speed in the specs ) and have wear and tear of the mechanical parts. They are also more expensive to manufacture compared to semiconductors switches.
Below is my sample circuit using an Arduino to drive a 12V DC Fan with a 12V relay.
- Arduino
- optoisolator 4N35
- 12V SPDT Relay
- 12V PC fan
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| 4N35 optoisolator |
An optoisolator is a chip that combined two circuits ( a LED & NPN phototransistor ) into an integrated circuit to isolate two different voltage. The Arduino is on 5V and the relay & DC fan is on 12V. According to the 4N35 datasheets, it can support up to 70V from pin 4 to 5.
See the circuit diagram below :-
When pin 12 is turn ON or HIGH, it will triggered the LED between pin 1 & 2 inside the 4N35 optoisolator (6 pins white chip) to turn on the phototransistor ( pin 4 & 5) and complete the circuit and send 12V power into the relay (black colour). When the coil is energize, you will hear a click and switch on the motor. The red wires are connected to 12V power supply.
Using this method, it can only switch on or off a circuit but could not control the variable speed of the motor. A second method will use a semiconductor, NPN Power Transistor model TIP122 to control the speed of the DC motor using PWM from pin 9.
On Part 2 of the article, I will explain on how to control the speed of a 12V DC fan using PWM.
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| Arduino 4N35 12V Relay |
When pin 12 is turn ON or HIGH, it will triggered the LED between pin 1 & 2 inside the 4N35 optoisolator (6 pins white chip) to turn on the phototransistor ( pin 4 & 5) and complete the circuit and send 12V power into the relay (black colour). When the coil is energize, you will hear a click and switch on the motor. The red wires are connected to 12V power supply.
Using this method, it can only switch on or off a circuit but could not control the variable speed of the motor. A second method will use a semiconductor, NPN Power Transistor model TIP122 to control the speed of the DC motor using PWM from pin 9.
On Part 2 of the article, I will explain on how to control the speed of a 12V DC fan using PWM.
Hi stan001,
ReplyDeleteFirstly, an excellent tutorial!
I just received my Arduino Uno yesterday, so forgive me for the dumb questions (to follow) as I'm very new to this.
I would like to do something similar to what you have done in this tutorial.
Instead of triggering a 12V DC fan, would like to trigger a 12V DC strike plate lock (for a security gate).
I presume that what you have done in this tutorial will suite my needs perfectly, simply by swapping out the fan for the lock?
Can you perhaps re-upload the enlarged image of your diagram, the current image is of low quality and it's difficult to see.
--
Regards,
William.
Hi,
ReplyDeletePls post the questions to the facebook group on the Useful Links above, there are project pictures and more interactions compared to this comments notes...
How would I control a DC motor with a real time clock. I would like to have preset times to operate the motor. Then I would like to preset a time to reverse polarity and run the motor in the opposite direction. Thank you Jeffrey.
ReplyDeleteHi. Please correct your Arduino pin power statement - your decimal point is off. This text should say
ReplyDelete"Arduino pins can only supply a maximum of 40mA or 0.04 Amp".
>>Arduino pins can only supply a maximum of 40mA or 0.4 Amp
ReplyDeleteThis is a rather old blog entry but I thought you'd want to fix this line anyways.
40mA is 0.04A, not 0.4A
:)
new to this topic i did not realize that there's a chip for this. i was using my IR emitter detector diode. but it was giving too weak output. i could light a small led but not a 6v motor. even though the battery was 6v. big thanks for the tip
ReplyDeletethanks!
ReplyDeleteHi there?
ReplyDeleteI am also new to this!
But since the opto-isolator can stand high voltage (upto 70V)
if we for ex. need to switch ON or OFF something wich is already have its own 12 V supply
( you can imagine any 12 V circuit with LED as load but somewhere a open switch with we can then feed into Emitter and Collector of Opto-isolator accordingly.)
So can we just use Opto-isolator as a switch ON or OFF
if required?
(I am sorry I am not good in explaining hopefully you understood what I mean.)
In facts I want to use arduino to do nothing more than switching ON and OFF a certain Switch which hence completes (closes) a certain circuit.
will this right?
Thanks.
@ScottInNH, thanks, error corrected.
ReplyDelete@Kase, if you just wanted to switch ON / OFF something on a 12V, NO, it does not work as the current passing thru the optoisolator (pin 4 & 5) might be too HIGH for the transistors inside to handle.
ReplyDeleteFrom the 4n35 datasheets, the collector max current is only 100mA.
@jeffery, yes, you can control the fan speed by the time of the day. If you would also like to reverse the polarity, you would also need a H-bridge to do that.
ReplyDeletehello..
ReplyDeleteI just wanted to know if you could help with the process to make the circuit for a line bot..
i mean a detailed explanation as to how to connect the Dc motors, relay, pot and everything? :)
Pls post yr questions on my fb group page...
ReplyDeletehello im trying to conect a 12v pump but i dont get how to connect the relay ?
ReplyDeletein the foto wich one is the collector, emitter, etc.
heres the code im using:
/*
* Trigger a relay
*/
int pumpPin = 12; // relay
unsigned long time;
unsigned long lastPumpTime;
int pumpPeriodHours = 6; // hours between pumps
int pumpPeriodSec; // seconds between pumps
int pumpDurationSec = 10; // seconds the pump is running
int statusPeriod = 5000; // ms time between status blinks-- to let you know it's alive
void setup()
{
pinMode(pumpPin, OUTPUT);
digitalWrite(pumpPin, LOW);
pumpPeriodSec =30; //pumpPeriodHours * 60 * 60; // seconds between pump starts
//pumpPeriodSec = 30; // for setting short periods when testing
}
void loop(){
lastPumpTime = millis();
// Activate the pump
digitalWrite(pumpPin, HIGH);
delay((pumpDurationSec*1000));
digitalWrite(pumpPin, LOW);
}
I use the optoisolator to control the relay...
ReplyDeleteSee this links on how to connect the reed relay : http://www.kpsec.freeuk.com/components/relay.htm
Future questions, pls post to my fb page... it is more interactive there with more people to help you with your questions...
can i know what ohm of resistor use ?
ReplyDeleteLike resistors on a LED, 220R or 1kR will do...
ReplyDeleteI appreciated your kind way of knowledge.Great Stuff Here..hope more to come.
ReplyDelete