Arduino and Optoisolators

Question

I am looking for an efficient (and safe) way to use the Arduino to switch a higher voltage device off and on. The first option would be a relay, but they are fairly bulky. I was wondering if I should use an Optoisolator instead ?

Here is a link to the Data sheet for the Optoisolator I am using..

http://www.everlight.com/file/productfile/el817.pdf I think (if I am reading it correctly) it expects an input voltage of 1V at about 20mA ?

However, I think it may be more involved than I originally thought. Here is a sort of simulation of what I am trying to achieve. http://tinyurl.com/y9xd7lzb

As you can maybe tell, I am using a voltage divider to reduce the output from the arduino (from 5V to 1V). My concerns are ..

1. Is this the best approach ?
2. Is it efficient ?
3. are there any problems I should be aware of ? Precautions I need to take ?
4. Is the voltage divider a good approach to feed the input to the Optoisolator ?

Also, efficiency is an issue as the Arduino (probably a Nano) will be running off batteries.

The target device is a 20V DC motor. I am a novice when it comes to electronics, so I would be grateful of any help or advice you can give.

Many thanks..

Dave.

• Jot: How much current does the motor need ? An opto-isolator is always a safe solution. Often a opto-isolator is used to control a mosfet, but there are also opto-mosfets. The EL817 is 1 mA to 60 mA with 20 mA as normal. It is no problem to use 10 mA. For 10 mA, you need ( 5V - 1.2V ) / 20 mA = 380 ohm. Just one resistor of about 330 ohm to pin 1 is okay (and pin 2 to GND).

Answer 1

Is this the best approach ?

Not really, no.

Is it efficient ?

No, far from it.

are there any problems I should be aware of ? Precautions I need to take ?

You don't want a voltage divider to power an opto-isolator. An opto-isolator won't be powerful enough to cope with the motor current. You need flyback protection.

Is the voltage divider a good approach to feed the input to the Optoisolator ?

No, definitely not.

Unless you require galvanic isolation all you need is a simple NPN transistor or N-channel MOSFET circuit:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

your optocoupler's 2ndary side isn't powerful enough to switch a load.

use the 2ndary side to switch a switcher, instead.