Endeavour
Posts: 14
Joined: Wed Feb 11, 2015 8:33 pm

16 Channel PWM IC PCA9635

Thu Dec 17, 2015 10:50 pm

Hi Guys,

I'm a bit confused about the usage of an I2C connection between the Raspberry Pi B+ and an IC.

I would like to use a 16-Channel-PWM-IC witch is configured via I2C and an Output enable pin. But the IC needs an own voltage supply since the pi is not strong enough to supply it. That's why i want to use a 12V supply and convert it to 5V. So they will have tow separate ground potentials.

Should i connect the PI GND to the IC GND or might this cause a current between the different grounds?

It might be useful to put a resistor between them or is there a better way to do this?

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mikronauts
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Joined: Sat Jan 05, 2013 7:28 pm
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Re: 16 Channel PWM IC PCA9635

Fri Dec 18, 2015 12:37 am

You have to connect the grounds for the I2C communications to work.

If you are worried about a possible DC offset between the two power supply's ground, get better adapters :)

Seriously, put a DC volt meter between the two grounds, if you get a non-zero reading, don't tie the grounds together.
Endeavour wrote:Hi Guys,

I'm a bit confused about the usage of an I2C connection between the Raspberry Pi B+ and an IC.

I would like to use a 16-Channel-PWM-IC witch is configured via I2C and an Output enable pin. But the IC needs an own voltage supply since the pi is not strong enough to supply it. That's why i want to use a 12V supply and convert it to 5V. So they will have tow separate ground potentials.

Should i connect the PI GND to the IC GND or might this cause a current between the different grounds?

It might be useful to put a resistor between them or is there a better way to do this?
http://Mikronauts.com - home of EZasPi, RoboPi, Pi Rtc Dio and Pi Jumper @Mikronauts on Twitter
Advanced Robotics, I/O expansion and prototyping boards for the Raspberry Pi

Endeavour
Posts: 14
Joined: Wed Feb 11, 2015 8:33 pm

Re: 16 Channel PWM IC PCA9635

Fri Dec 18, 2015 12:54 am

Thanks for the reply.

Is there something else that is important to know?

Using the gpio for the output enable pin does they pull to ground or do I need a pull-down resistor?

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joan
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Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: 16 Channel PWM IC PCA9635

Fri Dec 18, 2015 9:25 am

Endeavour wrote:Thanks for the reply.

Is there something else that is important to know?

Using the gpio for the output enable pin does they pull to ground or do I need a pull-down resistor?
Why not just connect the output enable to ground? That way it will be permanently enabled (assuming it is an active low signal).

If you do want to control via a GPIO you can connect the Pi GPIO direct to the output enable pin of the chip. Put a resistor in series if you are worried (5-20k say).

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