Using uln2003a ic with PCA9685 servo driver

Using Arduino Project Guidance
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Hi all I am quite new to arduino and lately I have been experimenting about led strip lights for arduino. I am currently doing a project where I need to control 14 rgb led strips that need 12V to operate. Since I need to control each of them individually I am planning to use uln2003a darlington array ICs to switch ground connections to the strips. But I will need 42 pwm pins from my arduino mega to control the strips. So I decided to chain 3 of PCA9685 servo motor drivers together. I want to know if it is possible to control uln2003a ics using this type of driver and if it is possible how should I wire the ic to the PCA9685 driver,

All your contribution will certainly be appreciated.

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The outputs of the PCA9685 can be connected to the ULN2003 directly.
But note the current limitations of this chip. About 150mA per output when all outputs are in use. Meaning your LED strips can only be a few LEDs long.

14 LED strips... Is this for two 7-segment displays?

Why didn't you use addressable LED strips.
They don't need drivers or PWM pins, and one Arduino pin can drive them all.
Leo..

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Hi, thanks for the advice, really appreciate it. When I connect uln2003a in to the servo driver what voltage do I need to put into the v+ pin in the servo driver?

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Does anyone else have any ideas about this?

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The V+ pin is for the servo power pins. The VCC pin powers the IC.

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Yeah mr surfer tim I knew that but to power my uln2003a ic plugged into the servo pins what can I use for the v+ pin? Thanks for the contribution.

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AFAIK, you can put any voltage you want on V+ as long as it doesn't burn out the devices connected to the servo power pins. Is 12v your goal? Shouldn't be a problem. Just don't connect a servo.

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But isn't there a max voltage rating

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On a servo, normally 6v on V+. You aren't using a servo.

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Screenshot_20240609_153746_Samsung Notes
Screenshot_20240609_153746_Samsung Notes1790×376 112 KB

I found this online about the v+ pin

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That sounds right. V+ is connected to the servo power bus (top pins) ONLY!
What that is stating is don't connect V+ with Vcc. It will overpower the IC.

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Thanks very much for clearing my doubt up Mr surfer tim. But another question I have is rgb strips tend to need a current of like 150ma to run and if all pins are turned on is it safe to power it through the board then?

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Shouldn't be a problem. Some servos are power hungry little devils.
Ensure your power supply connected to V+ is up to the task.

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Ok Mr surfer Tim thanks for contributing your time to my project. I will try what you have suggested and let you know if it works out right and again I really do appreciate it.

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image
but wait I just found this while researching more

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That applies to the signal lines not the power bus.

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but i will need the pwm outputs aswell to give the led pwm

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Depends on the LED strips.
Most have a GND, power (V+) and signal.
V+ may require more than 25ma.
Signal line shouldn't.

Edit: If you are attempting to control a LED strip that has a data/control/signal line in addition to power and ground, this isn't the device.

Check out this page.

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Yeah Mr. Tim these were the strips I was talking about

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But I need to control 14 of these with one arduino but the arduino does not have 42 pins (3*14). So, I am using the servo driver now to get pwm for all the strips.