Author Topic: 12vdc led's on bobcat  (Read 1712 times)

Offline wwwgator

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12vdc led's on bobcat
« on: March 09, 2012, »
Hey all,
 I was experimenting with trying to drive some 12vdc RGB led modules in some plastic skulls I picked post holliday sale.

I did some research on the TLC5916 LED driver chip and turns out that this little buggar can sink upto 17vdc between 5ma and 120ma., per manufactures data.

to do this, I connected a 12vdc power supply with the (-) going to the common (ground) on the bobcat board and the (+) going to the common anode of the module. Then, taking separate return wires to the inner pins on  P3 (closest to the chip) for sinking.
 
You will probably want to resize R7 current limiting resistor for your peticular LED modules

formula is  R= (supply V - V drop)/I
In my case R= (12- 2.1) / 30ma for roughly a 330ohm resistor for R7

make sure to not use the outer most pins on P3 as those have 6V on them.

This lights my little skulls up quite nicely

Experimentation continues.....!
I know nothing......and I prove it DAILY!!!

Getting crazy ideas and breaking stuff since 1977

Master Electrician/ Electrical Inspector/ Evil Genius (apprentice)

Offline rm357

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12vdc led's on bobcat
« Reply #1 on: March 09, 2012, »
The MR16 works the same way, but the output has been beefed up with the mosfets. Unfortunately the MOSFET inverts the signal, but it is still ground-switching the LEDs, not source-switching. As you have indicated, this opens up the possibility of using different source voltages literally on a pin by pin basis...

RM
Robert
Warner Robins, Georgia, USA

Offline rm357

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12vdc led's on bobcat
« Reply #2 on: March 09, 2012, »
Oh, for the MR16 there are two firmware files available. One for low power (without the mosfets) and one for high power (with mosfets) to account for the inverting introduced by the mosfets.
Robert
Warner Robins, Georgia, USA

Offline mkozik1

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Re: 12vdc led's on bobcat
« Reply #3 on: October 19, 2012, »
So quick question here, I should also be able to drive a small 12cDC relay from here as well correct?  And, I should not have to change R7 as the current for the solenoid is not that great.  Or am I way off base here?

Thanks in advance,
- Mark

Offline rm357

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12vdc led's on bobcat
« Reply #4 on: October 20, 2012, »
Two things...

When driving relays, be sure to get a relay with the shunt diode in it or plan to add a fast switching diode across the relay. The relay is an inductor which, in non technical terms, gives the current flowing through the relay some inertia. When you turn the power going to it off, that flowing current has to go somewhere, or it will pile up and create a negative high voltage spike than can damage the solid state driver. A diode installed in parallel with the relay with the correct polarity will block when the power is applied, and when the power is turned off allow the current to flow in a small loop at the relay until it stops. Think about pushing a loaded grocery cart. If there is no diode, you push the cart into the wall every time you turn off the relay... Eventually something will give...

How much current the relay needs depends on its size and construction. I think the bobcat servo controller currently has a 1k limiting resistor, which is only going to give you maybe 10ma per channel at the header. If you plan to push higher currents you may want add a little stick on heat sink to the chip...
« Last Edit: October 20, 2012, by rm357 »
Robert
Warner Robins, Georgia, USA