LED Strip controlling with Raspi - a check before my order

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Jonniboy
 
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LED Strip controlling with Raspi - a check before my order

Post by Jonniboy »

Hello adafruit members,

It's fascinating what you have done before and now I want to build my first project by myself.
I'm new in electrical engineering (or rather electrical hobby tinkering :D) and so I'm not sure if my construction works.
It's mostly copied from a tutorial on adafruit, but I have a question that doesn't go out of my head.

I want to control a LED multicolor strip (4-channel with R, G, B and V+) with my RasPi because of my idea that I see the light turns on (with the right color) when I get a message at Skype, Facebook or other social platforms.

That's the breadboard overview:
http://jonni.it/static/private/pic/led_ ... latine.jpg

You can see my question on the picture I've linked over here.
But here is it directly: Comes the energy from the DC Input only (to power the interface, the Pi Header, the LED strip etc.) or from the Raspi too? Is there a conflict?

And if no, will the construction works and how can I connect the DC Input with cables correctly (without lightning strikes in my room :D little joke)?

Thanks for any reply.
Best regards,
Jonniboy

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adafruit_support_bill
 
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Re: LED Strip controlling with Raspi - a check before my ord

Post by adafruit_support_bill »

The power should come from your DC input. The Pi will not be able to supply enough power. Just a couple of points:
1 - You will need to connect the ground from the Pi to the ground from your other power supply, so you have a common ground reference for the control signal.
2 - You show a 12v supply. But your strip says 5v.

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adafruit_support_rick
 
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Re: LED Strip controlling with Raspi - a check before my ord

Post by adafruit_support_rick »

You are using an analog RGB strip? Your connections to the PCA9685 are not correct. R, G, and B should each go to a PWM pin. You should connect ground to each of the three GND pins as well.

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Jonniboy
 
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Re: LED Strip controlling with Raspi - a check before my ord

Post by Jonniboy »

Hello and big thanks for your answers.
adafruit_support_bill wrote:1 - You will need to connect the ground from the Pi to the ground from your other power supply, so you have a common ground reference for the control signal.
How do you mean that? The Pi Header (and you can see, the Pi Header is connected to the ground) and I thought the ground from the Pi is automatically connected with the ground pin from Pi Header. Or is that wrong?
adafruit_support_bill wrote:2 - You show a 12v supply. But your strip says 5v.
I've forgotten to say that I don't use the LED strip which I've used in Fritzing. But I couldn't find a better object in Fritzing.
Here is the LED strip which I will use (3m, I think it's analog):
http://jonni.it/static/private/pic/led_strip.jpg
And that's the board which the LED strip uses before I came to the idea:
http://jonni.it/static/private/pic/20140829_183358.jpg
There you can see that the output is 12V with 2A.
adafruit_support_rick wrote:You are using an analog RGB strip? Your connections to the PCA9685 are not correct. R, G, and B should each go to a PWM pin. You should connect ground to each of the three GND pins as well.
Ok. First correction: http://jonni.it/static/private/pic/led_ ... atine2.jpg
The ground (black) should be connected to the ground pins near the PWM pins, is that right?

Regards,
Jonniboy

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Re: LED Strip controlling with Raspi - a check before my ord

Post by adafruit_support_rick »

Looks like you already have the common ground between the Pi and the power supply.

For the R, G, and B lines, you also want to connect the individual grounds from pads 1, 2, and 3.

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Jonniboy
 
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Re: LED Strip controlling with Raspi - a check before my ord

Post by Jonniboy »

Thanks for your answer.

I'm not sure if you mean that, but is the correction right at the bread board?
http://jonni.it/static/private/pic/led_ ... atine3.jpg

Best regards,
Jonniboy

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adafruit_support_rick
 
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Re: LED Strip controlling with Raspi - a check before my ord

Post by adafruit_support_rick »

That should do it, yes.

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Jonniboy
 
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Re: LED Strip controlling with Raspi - a check before my ord

Post by Jonniboy »

A big thank you to everyone who helped me.
And sorry if I annoyed you with my nooby questions :D

Now there is my last question:
Image
The "1" at the N-channel mosfet should be a "3", that's my fault.
Have I forgot something in this list? The power supply from the old board should fit in the DC input.

Regards,
Jonniboy

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Re: LED Strip controlling with Raspi - a check before my ord

Post by adafruit_support_mike »

Hi - I'm the Adafruit transistor geek. Rick asked me to double-check your circuit before you placed the order.

Your circuit looks good overall and the items in your order match the circuit diagram, so you're good there.

I do have one suggestion though: instead of powering the 16-channel PWM controller from the RasPi's 3.3v pin, use the 5v pin. The circuit you have it now will work, but will work better if it has that extra 1.7v.

The IRL8721 N-mosfets we sell start to conduct electricity when the gate voltage is about 1.8v higher than the source voltage. If you take the gate voltage up to 3.3v, the resistance through the channel will be a few ohms, which is pretty good. Thing is, if you take the gate voltage above 4.5v, the channel resistance drops to a few thousandths of an ohm. At that point, the mosfet conducts electricity almost as well as the wires leading to it.

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