I am creating a project where i want to drive my telescope using an Arduino,
So my computer is a Mac, and i have vmWare installed running Linux (Raspberry Pi) with Lin_Guider tracking software.
I purchased a standard xbee clone USB to Serial port converter, which i have tested with an array of LED's on the pins to make sure that the Computer and software can see the hardware and respond to tracking an item through the camera, and drive the serial ports. All this works well.
The next stage is to connect this up to a Arduino Uno board, and the Arduino to a L298N dual H Bridge driver board.
The two motors i am looking at are 12v DC reversible 0.6rpm motors. which has a nominal current 0f .1A,
I want to protect the three boards from each other, and was looking at building two separate boards which contain resistors, diodes on the input's to a quad Optocoupler IC, and the outputs through 2N2222 transistors to the next board.
I don't know if what i am doing is overkill, Will the extra boards provide protection ? logically i can't see why it wouldn't work, but i have never built anything quite as complex as this before.
I have seen other solutions on the internet, and i think the XBee / Arduino / L298N is the right choice, but some solutions mention adding transistors etc... where other options aren't using any other protection.
Any comments, guidance or assistance would be gratefully received.
It sounds overkill to me. 12V and 0.1A (if you are sure the current is that low) are hardly dangerous levels. You should be able to mix them with 5V or 3.3V logic on the same board.
There seems to be a lot of conflicting advice on the internet regarding this sort of configuration, from
"Just throw it together, it will be alright"
to
"You have to protect against stall current, blahh blahh blahh"
As mentioned before i am a complete novice when it comes to Arduino, well anything electrical really, I know what i want to achieve, i have looked it up on the internet, and the common theme is the Arduino, everything else around the edges is all different.
I appreciate all of your comments, and i will continue to investigate, especially with the MOSFET.
Motor stall currents can be 5x normal, maybe more, but that's still only 500mA. Some extra wide PCB tracks would be wise.
The suggestion from Tom was not to use discrete MOSFETs, but to use a modern motor driver chip that includes MOSFETs on the chip. These are more efficient, create less waste heat etc.
For that small current, something like a TB6612 motor driver would be appropriate. That's the same chip used on the Adafruit motor control board (V2) so you can buy one of those boards to test with. Or buy the breakout board that's not a shield and you can use that in your final project.
Generally the best protection is to put everything on one PCB inside one box. That way you can't plug the different boxes together incorrectly. It also reduces the number of places that interference can get in.
jon_street:
What do you mean by extra wide PCB tracks
Most PCB tracks only need to carry data signals and can be very narrow. Narrow enough to pass between the solder pads of a chip, for example. Tracks that need to carry significant current need to be much wider. The exact with depends on the thickness of the copper on the PCB. If you Google for PCB track current capacity, you should be able to find advice on how wide a track you need for a given current and copper thickness.
