carbenium
Posts: 2
Joined: Fri Jan 26, 2018 7:39 pm

electronics to controll four LED stripes individually

Fri Jan 26, 2018 7:53 pm

I have consulted this forum a lot as a reader, but this is my first post, so: Hello everyone!

Although I am not completely new to the raspberry pi, this is now my first electronic project.
The plan is (among other things) to be able to dim four strong LED strips (24 volts) individually. I have done my share of research and decided to control them with the raspberry pis software pwm and a MOSFET setup.
I found this four channel MOFSET which seems to do exactly what I need:
http://arduino-info.wikispaces.com/Bric ... rFetSwitch

My question: as this board was developed for arduino and arduino supplies its GPIOs with 5V i was wondering if the raspberry pi with its 3.3V can switch these MOFSETS efficiently/completely.

Has anyone here experience with the 4-channel switch? Or is someone able to read the electronic scheme and documentation that are provided at the site and to tell me whether this board would work also at 3.3V? Or finally, do you know suitable alternatives?

Thanks a lot!

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rpdom
Posts: 15572
Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: electronics to controll four LED stripes individually

Sat Jan 27, 2018 7:51 am

The board has opto-isolators, which is good. Looking at the specs you should be able to drive it directly from a GPIO with no problems. Connect the GPIO pin to pin 3 of the channel input and Pi Ground/0V to pin 1. There is no need to connect pin 2. There is no need for any other connections to the Pi. By my calculations the input will take between 3.8 and 5mA from each GPIO, which is well within the safe range.

The power to drive the mosfets comes from the + and - pins. These will need the stated 9-12V supply. The current required should be minimal, so a small 9V battery might do the job.

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Mortimer
Posts: 924
Joined: Sun Jun 10, 2012 3:57 pm

Re: electronics to controll four LED stripes individually

Sat Jan 27, 2018 8:47 am

There might be a problem using that board with 24V lamps.
The board appears to require 12Vdc to drive the output stage and this is coupled with the + output connections.
The optoisolator output stage may be tolerant to 24Vdc on the Vpp rail, but I would worry about the mosfet gate voltage being a little high.
You might get away with ignoring the + output connections and sinking the current from your LED strips into the - connections. Then you would need 12Vdc for the board and 24Vdc for your lights.
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carbenium
Posts: 2
Joined: Fri Jan 26, 2018 7:39 pm

Re: electronics to controll four LED stripes individually

Sun Jan 28, 2018 12:36 pm

Thanks to both of you for your answers.
So if I want to use this board it would be wiser to swithc to 12V Strips, which is still an option.
I am still concerned, that the 3.3V from the GPIO are not sufficient to turn the MOSFET on all the way (I am really not good in electronics, I read about this here: https://electronics.stackexchange.com/q ... to-be-limi)
Would that work effiviently with 12V strips?

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