ULN 2003 (Darlington Driver) TIP!

[nevcams]

Hi, just incase there are any novice's out there that are stuck using a ULN2003a like I was yesterday. I was trying to read the voltage out of the ULN2003a to power four
12 volt LED's. I had 4.5 volts from the #picaxe 14m2 I was using to out pins 2,3,4,and 5.However you can't read the voltage at the output of the ULN2003 as it is switching the 0-volts. (I discovered this at the expence of a new picaxe 14m2) Hope this is some use.

 

[Dippy]

I recall many novices having had similar experiences but it is worthy of note.

It's a bit like measuring I2C lines without a pullup resistor.
Any open low side driver will experience the same problem.
For testing just chuck a suitable resistor (or res+LED) between pin and +ve.
I would also suggest a little background reading including the Data Sheet which shows the configuration.

 

[Technical]

Also descibed in the FAQs:

http://www.picaxe.com/FAQs/Fault-Finding/

 

[westaust55]

This also applies to the frequently use ULN2803 8-channel Darlington driver chip.

 

[nevcams]

Thanks for your help and suggestions, I was warned that this new hobby (picaxe) of mine was addictive..... seems they were rite.
The amount of help and support for these picaxe's is amazing... (it's also good to know im not the only idiot)

 

[MPep]

(it's also good to know im not the only idiot)

Yup, plenty of us out there!! LOL

 

[Rbeckett]

(it's also good to know im not the only idiot)

Yup, I'm dumb as a post and just started learning basic electronics too and these folks do take pity on the terminally stupid like me. Have fun and don't get discouraged.
Wheelchair Bob

 

[Axel87]

Hey all,

Trying to run a 5v relay with a ULN2003, my first go with these.
I cant get the relay to activate.
Been having trouble wrapping my understanding around this.
From the manual-
http://www.ectinschools.org/images/design/advanced/buildingblocks/image021.jpg
Another diagram I have found-
http://i14.tinypic.com/29mljqb.jpg

I have a 12v supply to a 7805, 5v supply connected to picaxe and 2003.
Pin 8 of the 2003 is to gnd, pin 9 through the one leg of relay the other to gnd.

Does anyone have any idea how to clear this up?
Thanks guys!

 

[Buzby]

Hi Axel,

The two images you linked to are two different chips.

One is the ULN2803, with 8 circuits, and the other is a ULN2003, which has 7 circuits.

However, they both work in the same way, but the pin numbers are different.

Which of these two chips are you using ?

 

[erco]

See page 2 of http://www.parallax.com/downloads/stepper-motor-documentation

Shows exactly how to hook up a stepper motor, but it would wire up the same as four relays.

 

[westaust55]

By way of some simplified explanation that may help you understand the ULN2003 and ULN2803 8-channel Darlington switches.

These act like a low side switch.
When the input pin (from PICAXE) is low the switch is off or open circuit.
When the input pin is high the switch is on/conducting (in mechanical terms closed)
One side of each switch is connected internally to ground (0 volts).
So when the Darlington is off the output of the ULN2x03 is floating, and when the Darlington is on the output of the ULN2x03 is conducting to ground.
Accordingly, your load must be connected from the supply voltage to the ULN2x03 output (and not the ULN2x03 output to ground).