Providing Power to External Components

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ryanemp
Beginner
Posts: 8
Joined: Fri Jul 06, 2018 6:53 am

Providing Power to External Components

Post by ryanemp » Wed Feb 06, 2019 3:55 pm

Hi and thanks for any help you can provide.

My question is about the voltage and providing power to a new sensor or motor I may add:

From the Power Distribution Section on the Hardware Explained page
(https://wiki.bitcraze.io/projects:crazy ... :explained)

From that table:
Use the digital supply for a component rated <100 mA. So hook up between VCC and DGND.

For <1 A, use VCOM and GND.

I usually think of COM as 0 Volts, but here it seems I should hook my + up to either the VCC or VCOM and the - to GND or DGND. Is that correct or is there a reason for the difference?

Is this the best way to power external electronics? Seems like there's a lot of warnings about using LiPos so I didn't want to tie directly into the +BATT. I also wasn't sure if I could use the analog signal as an option.


Background:
I'm using this as a platform to learn more about embedded controls and C. That's why I'm working on adding other motors, sensors and components, besides just using it for flying.


I did go through the schematics for the decks. So for example the LED-ring schematic shows VCOM going to VIN on a chip on the deck. So I think I'll be ok, but I'm not 100% certain I have it right .

But I really want to make sure I don't damage my new prized possession!

Thanks again for any help you can provide, hope this is helpful for others as well.



arnaud
Bitcraze
Posts: 2046
Joined: Tue Feb 06, 2007 12:36 pm

Re: Providing Power to External Components

Post by arnaud » Thu Feb 07, 2019 9:17 am

Hi,

First of all, this page is about Crazyflie 1.0, if you are using a Crazyflie 2 the story will be a bit different and you will connect to the deck connector instead: https://wiki.bitcraze.io/projects:crazy ... ort_pinout. Both uses similar terminology though.

You are correct for using VCC for <100mA and VCOM for <1A, vcc is on the same rail as the rest of the Crazyflie electronic so it should be used only for low power sensors to makes the boards easy to design, we use VCOM and a regulator on most of our Crazyflie 2 decks.

VCOM stands for Common Voltage in this case, this is the voltage source that is shared to generate all the other regulated voltage of the system. It is connected to VBAT when the Crazyflie is running from battery and to VUSB when the usb power is connected.

On Crazyflie 1 there is 3 grounds: GND, DGND and AGND. They are used in pair VCOM/GND, VCCA/AGND, VCC/DGND. The grounds are cable in 'star' the power supply. This design is mostly historical: originally Crazyflie 1 was using analog MEMS gyroscopes, so isolating the analog circuits from digital noise was important, mostly on a 2 layer PCB design. Crazyflie 2 does not have all these voltages and grounds, it is a 4 layer design and there is one full layer dedicated to ground, furthermore there is no analog sensor in Crazyflie 2.

The lipo batteries of Crazyflie have a protection circuit so it would be quite hard to break them, though you should of course avoid shorting VCC or VCOM. The safest is to use VCOM and to generate your own voltage from it, this way you are sure to not affect the rest of the Crazyflie electronic.

ryanemp
Beginner
Posts: 8
Joined: Fri Jul 06, 2018 6:53 am

Re: Providing Power to External Components

Post by ryanemp » Thu Feb 07, 2019 10:07 am

Hi Arnaud,
That's all very helpful. Thanks for laying it out so clearly and explaining the terminology.

Yes, I am using 2.0 which sounds like it's even simpler:
VCC for < 100mA and VCOM for <1A.
Both will go to the shared Ground.

With the VCC and the VCOM, it is always on.

If I wanted to turn one of them off, I'd just use one of the GPIO (such as shown in the LED Schematic). Is that rated to 100mA also?

Thanks again and I've really enjoyed showing how thorough these forums are to some of our engineers here at work.

It helps to dispel the common comment that Open Source means On Your Own!

Have a great weekend :D

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