3 replies to this topic

[pettijohn]

I'm looking at some LED strip lights / tape lights and controlling them with Netduino 2. Looking at a few product listing and auctions to buy them (see the attached pic) there appears to be a +12VDC pin and then individual grounds for each of the RGB colours. It looks like PWM is used to dim and/or create various colours, though you can just buy dimmers and controllers as well.

 

How might I drive something like this from Netduino? Is it safe to use the 3.3V Netduino to drive a transistor as a switch for 12V, or will I just likely fry my Netduino?

 

If it's not safe to drive with a transistor, do I need to use relays? Do relays exist that switch as fast as is required for PWM? Would I need optical SSRs? 

 

Thanks for the input. 

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[CW2]

Is it safe to use the 3.3V Netduino to drive a transistor as a switch for 12V

 

Yes, it is safe. You'd probably want to check out transistor datasheet to see what base current (BJT) or gate voltage (MOSFET) is needed to switch your load current. Sometimes, another 'small' transistor is needed to switch the 'big' transistor; it also depends on switch topology ("low-side" NPN/N-channel vs. "high-side" PNP/P-channel).

 

If it's not safe to drive with a transistor, do I need to use relays? Do relays exist that switch as fast as is required for PWM? Would I need optical SSRs?

 

[Mechanical] relays don't work well for PWM, they are slow and will wear off quickly (due to contact arcing). SSRs are much better.

[rharding64]

consider i2c based RGBA solution, this is for SMD tri-color LED.

 

http://www.nxp.com/p...es/PCA9633.html

 

Cheers.

 

Ron

[rharding64]

On your concern with respect to driving higher current loads, 

 

consider using an optocoupler to drive your VCIS BJT, if set up as open collector switch.Collector attaches to cathode of the LED. once BJT is driven ON, the collector node looks like ground and the LED turns ON.  

 

Ron