Newbie needs help for ULN 2003 (not 2003 A) help with 89s52

My program is simple to light led's with the cheapest option uln2003,

Led's not connected directly to processor because max current through 89s52 should not exceed at any time more than 71mA.

right now only three led's are connected, each connected to 40mA current.

The uln2003 connection is per the datasheet of uln 2003.

the uln 2003 does operate when a single led is connected, however after connecting multiple led's (3 ) one led lights ok , second led lights a little dim and the third led does not lights. The story is same with the different pins of uln2003.

Uln2003 connections are
input pins connected to mcu p1.0 to p1.2
outputs connected to -ve side of led
pin 8 of uln2003 is connected to -ve
com pin is not connected.

My project needs the led's to be switched on and off at least 1/10th of a sec

when mcu starts:
p1.0 is 1 and p1.1 and p1.2 is 0
after 10ms
p1.0 and p1.1 is 0 , p1.2 is 1
after 10ms
same as above.



what can you guys recommend ?
diodes between mcu and uln2003?
or
resistors between mcu and uln2003
or
com pin of ULN 2003 to where ??
or
ULN cannot switch fast enough?

I am totally new to this area so a much descriptive reply is requested

Thankyou for your time and help in advance

Mokko

Try pulling all the uln's input pins with 10K resistors to Vcc. Cheers.

10ms is too fast that your eye can see

1/10th of a sec is not 10ms and is 100ms

No need to connect com pin in your circuit

You need to have a resistor inbetween mcu and uln

Nandhu

Re: Newbie needs help for ULN 2003 (not 2003 A) help with 89

Thanks to both for replying so fast,

Please let me try both of this one by one. It will take a day for getting the resistors and using them in the circuit.
i will post results tomorrow.

sorry about the time shown, its not 10 ms but 100ms
i.e. 1/10th of a sec.

thanks once again.

Re: Newbie needs help for ULN 2003 (not 2003 A) help with 89

Hi,

This might help

Re: Newbie needs help for ULN 2003 (not 2003 A) help with 89

Hi guys,

I guess Edaboard was down or something cause I couldnt open the websitelast few attempts.

10k resistors didnt help,
will try with the 250ms setting now.
Also the board I am using also seems to be a part of the problem.

I am getting a new unused and cleaner board , will arrive in a week or soo.

once again thanks

Re: Newbie needs help for ULN 2003 (not 2003 A) help with 89

I guess Edaboard was down or something cause I couldnt open the websitelast few attempts.

Click to expand...

No, it is working fine here.

Nandhu