PDA

View Full Version : l293d trouble for newbie

jagat02
12-18-2005, 11:58 PM
I am trying to build a robot with 3 friends.However, we are all new at making a robot.

We have bought a RC toy car.The motor has been removed and at first we are just trying to run it with l293d IC.We have read the data-sheet.
For a regulated supply of 5V we have successfully used a 9V battery and 7805 to get output of 4.99V... :) ..This logic supply is being given to pin 16.

Pins 3 and 6 are connected to the two terminals of the motor.
Pin 8 has been connected to +end of a 9V battery for motor supply voltage.

Pins 4 and 5 and -end of the battery have been grounded .

Now, the problem is we really dont know what to do to pins 1(enable), 2(input 1) and 7(input 2) so that we can run the motor. :?

It seems that a uC(microcontroller) has to be connected with those 3 pins.If yes, then how to do so and which uC will be suitable?

Pls help us out...

Rgds/Jaggu

docel
12-19-2005, 01:29 AM
hi,
L293d is 2 motor drives:
3 & 6 to motor1; pin 1 to enable motor1; 0=OFF, 1= ON (POWER on/off)
2 & 7 decide direction of motor,. eg,. 2=0, 7=1 clockwise rotation; 2=1, 7=0 counterclockwise rotation

11 & 14 to motor2; pin 9 to enable motor2; 0=OFF, 1= ON (POWER on/off)
10 & 15 decide direction of motor,. eg,. 10=0, 15=1 clockwise rotation; 10=1, 15=0 counterclockwise rotation
Same for the othe rmotr driver...

yassh
12-19-2005, 10:57 AM
there's another problem. The enable pin(1st) is drawing too much current(180mA) and thanx to that, the supply deviates from the regulated 5V
This is when i'm only giving a 5V to enable without doing anything to the other pins.
Using 7805 for supply, with a 10micF capacitor in parallel

Also how close to 5V do we need to be for a 1 logic state?
The data sheet says it's 0 till 1.5V.

12-19-2005, 12:04 PM
connect pin 1 to 5v.....
give logic levels to input pins 2 and 7
if both 2 and 7 are high.... the motor stops...
if both r low... braking.
and give 10 or 01 to make the motor move in either direction.
as far as the problem which u said about the fall in voltage of 7805 ...
it happens...
i ve had similar experiences.... but still there r certain 7805 where the voltage doesn gets down. it comes at a little higher cost too.
i think its manufactured by ST... u ll get it in railton electronics[ chadni chowk, calcutta].
and even if u r not running motor, the chip ll draw about 40ma.
there is hardly anything tat u can do avoid this....

docel
12-20-2005, 01:04 AM
yassh/jagat02,
Sri forgot: DO NOT CONNECT ENABLE PINS 1, 9 TO +5V DIRECT!!
1. Use 10k resistance from + to enable pin. Current should be <1ma and Venable should be 3v.
2. use 1ufd tantalum in place of 10ufd at the 7805 output pin.
3. 180ma....could have blown the chip!

yassh
12-20-2005, 04:44 PM
We've tried out almost everything we could think of.
gave regulated 5V supply to pin2 and 16.
9V supply to pin8(Vs)
As for the enable pin, we've tried 2.4V, 3V, 5V, 7V...
connected pin7 to ground.
the potentials of both pin3 and 6 are at 0.10-0.15 w.r.t grnd in all cases.
In some cases the IC was heating up, and we switched off the supplies to avoid overheat.
Vs, pin1 supply and 5V regulated came from three different power sources.
The regulator output was always between 4.95 and 5.00 except when pin1 was connected to it.

The voltages were measured using a multimeter in parallel.
To measure the current, I connected the multimeter in series between the pin1 supply and pin1, and took the (milli)amperage reading. In all the cases that we tried, the current was >175mA.

As a last resort, we tried replacing the IC(L293D) with a spare one that we had bought, but to no avail. In fact, this time pin16(logic supply=5V) started drawing a lot of current>100mA

We used 9V HiWatt batteries for regulator input and a variable outVoltage AC-DC adaptor for pin1 and a separate 9V for Vs. We checked the circuit many times over and the pins were getting what they needed.

We're totally confused as to what to do next.

BTW, I just saw a post by dr0w in another thread where he suggests pin1=0 is for motor ON and vice versa. Is that true?