DC motor from 89c51.help reqd

hi,
i found this site recently.ppl here seem to real time experts.
I personally am doing a project for lift or elevator .This is my post on interent regarding the need to drive my dc motor.iam doing the project in a breadboard as of now.
the microcontroller output is not sufficient enuf to the l293d.
note:l293d requires 'high logic 1' input and gives max 36v voltage output.
i can make it run in my pcb(previously made,iam making new modifications to it ).but in my breadboard ,the o/p from the micro cont is not enuf to the l293d motor driver ic.
If i connect the input to 12 v supply then the l293d responds..even for 5v there is no response..
please help me. thank you

your need to tell more about your motor and the circuit your using you use the micro controller to turn on the L293D it in turns powers your motor from a higher power source
take a look at this site botom of the page it tell about L239
**broken link removed**
hope it helps

hi ,
the motor is 12v dc supply and input current would be <500mA..around 350mA...
yes,the microcontroller will give the input to the l293d and l293d is powered externally with 12V, 500 mA .
2 inputs from the microconttroller positive side and negative side of motor.
this situation works fine in pcb board..but the current o/p seems very low in the breadboard..
pls suggest .
thanks

hi,
sry..but thanks for ur quick reply yest.

You need to show your circuit it should be something like this but your using the L293 for the bridge. Use 1k resistors from your pic to motor input.

here a drawing of the L293D with 2 motors the pic is from
**broken link removed**

hi

**broken link removed**

hi,
i am using atmel 89c51 for the project.

jus for testing iam using just two pins from the 89c51 ,like in the picture.(sry for the ads)...
port 2
p2.1 (first pin) to high or logic 1
p2.2 to low
these two inputs are fed to the l293 as per ur above figure.
There is no response from the motor.
u mentioned ,to use 1k..can i use resistors below 1k?..

also i tried the high pin to my led,it glowed very lightly.
so i recently bought a transistor bc548(NPN) n bc 304 to amplify the logic 1 from the 89c51.

i hav checked online..i connected bc548 in the following manner.
i tried base to the input thro a resistor 330ohms
collector-to the short leg of led and the supply to the positive leg of led.
i.e collector is connected to 5v supply with led in between and a resitor.
emittor is grounded thro a resistor.

result: led glows brighter compartively than before on high input
doesnt glow on zero input
any other ways to improve the output..like modifiyin resistors to higher or lower value?
if i connect the transistor to 12 supply,iam able to run the motor
..is there any risk?..or better transistors to do the same work with 5v?..
i recently burned 4 atmels ,knowingly n unknowingly connectin to 12 v.
thanks again!
sam

i think there is a mistake...iam not sure of the transistor..my testing was wrong.
how can a transistor be interfaced in between before a motor?

The H-bridge is to power the motor. With the right H-bridge you can power any
motor with your micro controller. Your micro controller is to turn on the H-bridge . It doesn't take much to turn it on your using 4.5 volts for high and 0to 1.5 volts for low. You only need .2uA to turn the bridge on. If you would draw out how your setup is it would be easy to tell you what to do from what your saying your going to burn up your micro controller

this is for you micro

1. Under steady state (non-transient) conditions, IOL must be externally limited as follows:
Maximum IOL per port pin: 10 mA
Maximum IOL per 8-bit port: Port 0: 26 mA
Ports 1, 2, 3: 15 mA
Maximum total IOL for all output pins: 71 mA
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test conditions.
2. Minimum VCC for Power-down is 2V.

Click to expand...

Take a look at this maybe it will help you see how a transistor can
switch a motor on and off at a higher volt then your 89c51 and more current
you can burn up your micro by pulling to much current out of a pin or sinking to much in.

hi

hi again,
I dont knw how to tell,
but everythings started working yesterday..n i have been adding more n more components and everything seems to work perfect now..

the current from micro was enuf to the l293d...

i was kinda annoyed when nothing worked,but i tried for one last time yesterday,i re-did the entire circuit and everythin from the start...

n tried a few new things,lled display,n a buzzer n stuff..worked perfect..

thanks for looking thro the minute details for me..i never had the idea of fixing this issue..thanks for bringn them up..

i will post again,when the project is done,hopefully..will send a picture .
thanks