Hi everyone
First of all sorry for my bad English. I'm following this guide. I should use a L293D and 5-15v DC motor, but I have only a L293C and a 3v motor. Do you think it could work if I use them with two AA battery as external power? Is there any risk to burn my arduino/L293C/motor?
Thank you in advantage,
Giulio
ilfugiuliopascal:
Hi everyone
First of all sorry for my bad English. I'm following this guide. I should use a L293D and 5-15v DC motor, but I have only a L293C and a 3v motor. Do you think it could work if I use them with two AA battery as external power? Is there any risk to burn my arduino/L293C/motor?
Thank you in advantage,
Giulio
With any motor driver, you're going to see a voltage drop; with the L293, it's about 1.5 volts (roughly). If you look at the datasheet for the L293C, you will notice that Vs (supply voltage for the motor) at a minimum can be Vss (logic supply voltage), which in turn can be a minimum of 4.5 volts. So, what that means is:
- 3 volts (if using alkaline batteries) is -not- enough to run the L293 nor the motors.
- ...but 5 volts is nearly perfect!
So - if you ran the L293 on 5 volts (Vss) and the motor inputs to the L293 (Vs) at 5 volts, the motor would see (when you set the appropriate pins on the L293) 3.5 volts; that half a volt won't likely damage the motor (of course, you haven't given us anything about the true specs of the motor, model number, etc).
This is going to be the minimum you can do anyhow, because the logic HIGH output of the Arduino is 5 volts (unless you are running it from 3.3 volts, of course), which dictates that is the lowest for Vs on the L293C. I wouldn't worry about the motor.
One thing you -do- need to make sure of is to add the protection diodes on the outputs of the L293C (the "D" version includes them internally - hence, the "D" moniker) - otherwise the back EMF of the motor will ruin it in short order. Finally, provide a separate supply of 5 volts for Vs and Vss to the L293C - don't branch off of the Vout from the Arduino or anything (ie, don't try to run this and the motor using the Arduino's on-board regulator - it wasn't designed for this kind of load).
Thank you very much. Do you think it could work? Can I use Vin pin? Or do you think it's better to provide a completely separate power supply?
I didn't understand how to use the diodes. Are them ok in the image?
Thank you for your patience and help 
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ilfugiuliopascal:
Thank you very much. Do you think it could work? Can I use Vin pin? Or do you think it's better to provide a completely separate power supply?
Use a separate power supply - it's best.
ilfugiuliopascal:
I didn't understand how to use the diodes. Are them ok in the image?
No - that will not work at all. Look up the L298 datasheet; you should be able to find a version (there's a few floating out there) detailing how to use diodes with it; it's the same kind of circuit (the L298 doesn't have built-in diodes either). Or - look here:
That's how you use an L298. So, for the L293C, you would connect the diodes the same way on the motor outputs (note, if you are using two motors, you will need 8 diodes, of course). You might also want to add that cap (C1) - mainly for back EMF noise suppression.