Does anyone know any good reason to connect the enable pin to the microcontroller on the L293 motor driver?
Connecting this pin to 5V shouln't be enough?
This way I can use the microcontroller pin for any other use.
Thanks!
Yes.
Basically, your question is to use a 4-pin system or a 6-pin system. Here we go:
4-pin with enables pulled high (Direction pins: one is a digital i/o, one is a PWM)
- Simpler, less pins from the uC used
- You will have full forward/reverse with speed control
- No brakes, coast only
- Your PWM duty cycle will have to be inverted when using reverse (I.e. 75% PWM in reverse will result in 25% power)
6-pin (4 digital I/O pins for direction, 2 PWM pins going to enable)
- More pins used
- PWM control is consistant in forward and reverse
- You now have proportional braking
There is more but that is probably what you wanted to know.
You can always save a pair of pins
by using a NOT gate between the two input pins per motor like https://www.robotshop.com/letsmakerobots/node/32462
Tank you very much. One more
Tank you very much. One more question. It’s about the “No brakes, coast only” part. Using a modified servo would I notice the difference?
Brake/Coast
I don’t know for sure, but, I would imagine you might get a braking effect by sending a number just past center opposite the direction of motion.
As I was writing the above, I realized that plastic gears might not like fighting that much force, and, rather than a braking reaction you might get a breaking reaction. 
Modified servo…
Now I am a bit confused. I am going to assume when you say “modified servo” you mean you took ALL the brains out of the servo and are using it as just a geared motor now. If this is the case, then yes, braking stops your wheels pretty gosh-darn-quick.
If you are using a continous rotation servo (with brains, and with 180 stops removed) then you don’t need the L293D at all. Your servo is still a servo and contains its own motor driver.
In general, braking is like 4wd or air conditioning. You really don’t need it, but it is sure nice to have. If you are doing any kind of “precision” motion, (I.e. encoders on your wheels) I would say brakes are 100% needed.
Yes It has no brains. Now
Yes It has no brains. Now comes the tricky part. For more info, i’m gonna say that I’m using a PIC16F84A, and that i’m trying to design a circuit with two L293 to drive four motors. (That why I needed to do without the enable pins, because I needed to save some PIC pins).
As you can see in the picture below, a single pin from the microcontroller drives two pins (one on each L293). I can imagine that this could drive an excess of current from the pic so I’m thinking on some switching transistors. (if anyone can help me with that… :P) or if you know of a chip that can handle four motors…
No problem driving two chips
Current draw to drive the inputs on the L293D is not an issue it is in the microamp range per input.