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Electronics projects

Last update: 31/07/2015

L293D

One of the most interesting chip for robotic projects is the L293 produced by STM and Texas. It is a simple quadruple half-H driver (only 600  ma) designed to accept standard TTL logic levels, widely used to control small dc and even stepper motors (remember that the `D` version has internal clamp diodes).

 

It is really interesting because can be easily driven by a micro controller without waste power due the presence of  `enable` pins. Here follows the block diagram of the chip.

The L293 is sold in two different packages:  SO 20 pins (surface mount) and a power-dip 16 pin. Our examples will use the power-dip version.

 
 

 
 L293d dc
 

 
L293d and DC motors: 

A single chip enables the user to connect and control very quickly two small dc motors according to the following table:

Enable

 

Input 1 

Input 2 

Result 

 H    H  L  Motor turns right
 H    L  H  Motor turns left
 H    L or H L or H   Fast stop
 L    L or H L or H   Slow stop
 
The correct use of the enable pin is quite important to save battery life. The value of the VCC tension (according to the data-sheet) can vary between 5 and 36 volts.

The chip provides two complete channels therefore two small dc motors can be driven by a single chip.
The L293 has an auto over-temperature protection. It means that the chip will stop working automatically if the temperature gets too high and can be controlled very easily with any microcontroller.

The use of dc motors, however, will not allow a speed control of the motors as per the fact that the motors can have only an on-off or forward-reverse status. If the user needs of an exact control of the motors (relative to the speed and the position) another very quick solution is the use of stepper motors but in this case a chip can drive only one motor according to the fact that all half-H bridges are used.
.

 
 

l293d stepper

L293 e stepper motors:

schematic is similar, the main difference is that using a unipolar stepper motor we have to power the coils using the right sequence to control the movement (step) and the direction in the traditional step 2 phases mode:

 Full Step Mode

 

 Half Step Mode

 coil1

coil2

coil3

coil4

 

coil1

coil2

coil3

coil4

 H  H  L L    H  H  L L
 L H  H  L L H  L L
 L  L  H H  L H H  L
 H L L H  L L H L
         L  L  H H
         L  L L H
         H  L  L  H
        H  L  L L

 

 

 

 

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