AT89S52+uln2803 for Led driver.

[dwep]

uln2803 led

In my design,I try to use AT89S52+uln2803 for Led driver.Could I connect port 1(or 2,3) to 2803 without any pull-up resistors?
Someone said port1(or 2,3) can not output 1mA current.But I can not find the parameters on the datasheet.

 

[amol_shah]

uln2803

how many LED's do you want to Turn ON?
P1, P2 & P3 have internal 10k pullup resistors so the max o/p current will be 5v/10k=0.5ma (assuming 5v supply) but u can connect the anode to the Vcc & the cathode to the Port pin using a resistor. Under stady cndition 89s52 pin can sink 10ma current which is sufficient to turn ON a LED.
Check the following link for LED interfacing
https://www.dnatechindia.com/index.php/Tutorials/8051-Tutorial/LED-Interfacing.html

If you need to interface ULN 2803 to 89s52 then you will require a pull up resistor,
check this link for interfacing a Transistor to 89s52 you can replace the relay in the circuit with LED's.
https://www.dnatechindia.com/index.php/Tutorials/8051-Tutorial/Relay-Interfacing.html

 

[dwep]

uln2803+led

Thankyou for your reply.May be connect the anode to the Vcc & the cathode to the Port pin using a resistor is OK,as I only want to turn on 4 LEDs.
But I think with ULN 2803 between MCU and LEDs is helpfull for EMC.You see,the Leds will fixed outside the enclosures and other parts inside.I have saw may design with Leds fixed outside have a ESD problem.

 

[dwep]

uln2803 led driver

Another question: It seems that pull-up resisters may be cause error operation under the reset process.