I control a simple DC motor speed using PWM from Arduino and a BC547B transistor.
But I want to be super sure that Arduino and DC motor circuit are separated, so I need an optoisolator.
The problem is that I don't know how to connect the optoisolator, because it is more complicated than those described on forum. I'm using 6N138.
Please check, if the schema I drown is correct or not, and please tell what value should the RL resistor take. On page 6 from the 6N138 datasheet I know that it depends on output, but which one is mine?
Yes, think that's viable - the device's Vcc is limited to 7V so you need that voltage divider (make it divide to 5V, not 7V, BTW, 7V is the absolute maximum (we don't go there!)). I think a 10k resistor will be fine on the input, it claims 0.5mA drive doesn't it?
OK, so now its clear for me
For those who want to know something about RL: this resistor's value should be appropriate to give enough current to the transistors base. You should choose it carefully, because too much current can damage transistors base!
Today I went to the lab to check the DC motor parameters and to test the circuit.
I wrote down the motor serial numbers - I wasn't able to access the internet to check the parameters, so I assumed that the collector current will be smaller than 1,5A. I used BD135 transistor, with a proper resistor in front of its base. Then I've turned the power supply on and the motor stared rotating, even when there was no signal from the Arduino!
I disconnected the circuit and I've measured the current flowing through the motor in a basic circuit which contained only the motor and power supply - nothing else. The ammeter showed 11,6mA! The power supply voltage was 9,3V, so the power of the motor should be about 0,1W!
I realised that there can be something wrong with the transistor so I've changed it to BC547B which max Ic = 100mA. After that, the PWM control from Arduino worked, but the motor rotated VERY slowly. I've checked the current flowing through the motor and it was only about 4,6mA!
