FEZ Cream used to dim led strip

Hi All,

I was wondering if it possible to use the fez cream and pwm to dim a led strip using a n type mosfet ? I have read about This using an arduino are there any objections using a rasp 2 and a fez cream to make this work ?

Kind regards,

Wim

Hoi Wim,

does this help a bit [url]https://github.com/ms-iot/samples/tree/develop/RgbLedStrip/CS[/url] ?

Groetjes,

Peter.

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Hi Peter,

Thanks for your post the examples in the link al use ledstrips with build in chips. Which is something different from the ledstrip i use mine is just a simple 12 volt powered led strip which i must lower using a mosfet i think I am not an electronics whizz.

Groetjes,

Wim

@ Wim - What model of led strip do you have or can you provide a link to the arduino project ?

Hi Peter,

Fo show here is the information: Usage | RGB LED Strips | Adafruit Learning System they talk about dimming rgb led strip with 3 mosfets. But i would think this same trick would apply to a whit led strip just using 1 mosfet.

this is the strip i use

@ WE - Yeah, should do but you have be careful with the current draw from the ledstrip. 2.5 m * 0.2 = appx 0.5 Amps per color, since you only one color, that’ll do. The description in the adafruit link should be enough info to get you started. The mosfet takes up to 8 Amps so you have some head room left.

I’ve got it running from a micro controller to using netmf and pwm and the leds dimming is ok.

https://www.ghielectronics.com/community/forum/topic?id=22481

I have managed to dim the led using pwm of the fez cream. The only thing i don’t understand is that when the power is 100% the ledstrip does not have as much light output as when using the arduino. What can be the cause of this.

Regards,

Wim

@ WE - Is there a difference in output voltage / current ? Are you using the exact same LED strip ?

Hoi Peter,

When using the fez cream the mosfet only lets through 7.7 volt and when using the arduino its the full 12 volts how is it possible ? has it something to do with frequency and dutycycle ?

it is the same led strip i am using

Has it something to do with the fact that the arduino is running at 5 volts and the fez cream at 3.3 ?

yes it’s probably related to the voltage to the mosfet. You could use another transistor prior to the mosfet to allow you to bring in a higher voltage.

Hi Brett,

Thanks for your post because i am an electronics beginner can you point me in de right direction to what kind of transistor i need to make this work ? Do these transistors exist that can boot up a 3.3v signal to 5 v ?

Ahum, Wim did you connect the power of the ledstrip to 12, 5, or 3,3 V?

Peter the power from the led comes from 12v. The strange thing is everything is the same between the cream and the arduino both dim the led strip in the proper way only at peek levels the intensity of the led is poor on the cream. So when using the arduino using the same wiring it al works as expected

Do you have a bc547 or equivalent ?

hi peter i dont have one of those at the moment i reckon that is a transistor that boosts the signal from 3.3v to 5 v ?

Regards,

Wim

@ Wim - No just a common general purpose NPN transistor to boost the outcome of the MCU a bit as first stage before going to a TIP120 transistor

You try use level shifter as well, see if that gives a better result.

Hi Peter could you maybe show how i would use such a npn transistor to achieve my goal of converting 3.3v signal to 5v signal ?

Regards,

Wim

Try the following [url]http://www.electronics-tutorials.ws/io/output-interfacing-circuits.html[/url]

Hi Peter,

I have found a solution in the form of the sparkfun level shifter (https://www.sparkfun.com/products/12009) and this in combination with the mosfet dims the led. :slight_smile:

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i have been fiddling with dimming both the white cool color and soft color white led. I assumed that this was possible with the socket 7 of the cream the schematic tells me that it has three pwm pins pins 7 8 and 9 so i would have one to spare but only one color is dimming properly both other pins dont seem to dim when i change the dutycicle is there something in my reasoning incorrect ?

Regards,

Wim