3 - DC Motors

There now follows various circuits for driving DC motors. The circuit most suitable for your project will depend mainly on the current consumption of your motors.



3.1 - 600mA DC motor controller, up to 36v

The following circuit is based on the L293D which has several plus points for a minimal controller. The 'D' on the end of the 'L293D' means that it includes output diodes meaning that you need less additional components at the expense of a smaller current output.



For the L293D datasheet see http://www.st.com/stonline/books/pdf/docs/1330.pdf


This controller is limited by the abilities of the L293D:- it can provide 600mA per motor or a maximum of 1.2 amps for a micro-second.


The motor supply can be between 5 and 36 volts.


Each motor requires two pins from the micro-controller and this uses the 'tri-state switch' stage mentioned earlier.



This requires one tri-state switch per motor;

one L293D for every two motors. The L293D costs about $4.30

So about $6 in total - for driving two motors


NB I now recommend that you use an SN754410 instead of the L293D. This is a direct plug in replacement and has the advantage it can provide 1A rather than 600mA and it also costs about 98 cents !!!




3.2 - 1 Amp DC Motor Controller, up to 36v

There are two ways to do this:-


Either: use the previous 600mA circuit but replace the L293D with a Texas Instruments SN754410 which is a direct pin for pin replacement. This is the preferred solution as the chip costs 98 cents and you dont need the additional diodes.


Alternatively:- do the following.


This circuit is similar to the 600mA version except that:-

1. It uses the 'L293' rather than the 'L293D' See http://focus.ti.com/lit/ds/symlink/l293.pdf

2. This chip allows a higher current of 1 amp per motor but requires us to add the diodes at the output stage. These should be fast, ie Schottky, diodes that can cope with the 1 amp current and a reverse voltage greater than, or equal to, the voltage of your motors. The motor voltage is still limited to 36v.



This requires one tri-state switch per motor;

one L293 for every two motors. The L293 costs about $5.81

You will also need 4 diodes per motor. The cost of these will vary depending on the voltage of the motors, and the current, but lets say about 50 cents each - ie $2 per motor.

So about $12 in total - for driving two motors

3.3 - 2 Amp DC motor controller, up to 50v

This circuit is similar to the previous ones.

It uses the tri-state switch to control speed, direction, and braking.

Schottky output diodes are used that match the current and voltage for your motors.

The only 'real' difference compared with the 1 amp circuit is that we using an L298 rather than one of the L293 series. The L298 lends itself to mounting a heatsink, due to the higher current, but is a bit of a swine to solder onto strip board or matrix board and is more designed for PCBs. It uses a 'Mulitwatt 15' package - and comes with two strips of pins each using a standard 0.1" pin separation. But the problem is that the second bank of pins is offset by 0.05". So if you are using strip/matrix board then you will need to be very carefull when bending one set of pins to fit.


This requires one tri-state switch per motor;

one L298N for every two motors. The L298N costs about $3.57

four diodes per motor at about 50 cents per diode.

So about $11 in total - for driving two motors