NBV3 Schematic check please

[Generic Jedi]

There are three different equations you can use to find the wattage rating for a resiter. If you use the correct values in the correct places, they will all give the same answer.

P = power measured in watts
E = voltage measured in volts
I = current measured in amps
R = resistance measured in ohms

Equation 1: P = R x I^2
You take the resitor value from the resitor equation and multiply it by current squared.

Equation 2: P = E x I
You take the voltage (that's voltage supply minus LED voltage forward, just like in the resistor equation) and multiply it by current.

Equation 3: It uses the values for E and R to find P, but I don't remember the equation. I'll have to look it up when I get home.

[Generic Jedi]

Say you wanted to find a resistor for an accent LED that has a forward voltage of 3 volts to run at 20 mA. You use a 3.3 volt pad to power it.

For the resistor: R = (supply voltage - forward voltage) / current
That gives you: R = ( 3.3 - 3 ) / 0.02 = 15 Ohms

To find the wattage
Equation 1: P = R x I^2
Or : P = 15 x 0.02^2 = 0.006 watts

Equation 2: P = E x I
Or: P = ( 3.3 - 3 ) x 0.02 = 0.006 watts

You would still have to round the watt value up to a resistor you could actually find...

[Generic Jedi]

The third equation is: P = E^2 / R
E is voltage supply minus forward voltage: P = (Vsupply -Vforward)^2 / R

That gives us: P = ( 3.3 - 3 )^2 / 15 = 0.006 watts

[Count Voodoo]

The question I have now is silly, but its another tiny detail I am having trouble finding. If you look at the junction from the Momentary switch black wire to the Negative line going from the Recharge port to the Board Negative pad, do I just solder that at the negative post on the recharge port or straight to the board negative pad with the negative wire from the recharge Port? That would seem to be the same anyways, but I want to do it correctly when I do finally get the board. Thanks!

[Silver Serpent]

Whichever is easier for you. I find it's more difficult soldering a bunch of wires to the pad on the board, so I opt for the other method.

[Count Voodoo]

Ok great , thanks for the input SS! I figured it was most likely the same, but youre right, the more space I can free up on the pads the better!

[erlomd]

great wiring diagram!

but, I was told that resistors for each LED are not needed when connecting to the NBv3?

[FenixFire]

http://http://www.plecterlabs.com/Me...te%20v3-GB.pdf

Check page 9.

[erlomd]

http://http://www.plecterlabs.com/Me...te%20v3-GB.pdf

Check page 9.

I did...but on page 21 of the NBv3 manual it says & I quote:

"On the one hand, such a small resistor is unpractical to source and tolerance will not
lead to an accurate current limitation. On the other hand, not using a resistor will
overdrive the LED which might fry. The board driver can act as a linear, configurable
resistor, using the drive parameter. When getting such a small resistor value (below
0.5 ohm, AND Vled < Vcell), the drive can be calculated as follows:
drive = 1023 * (Vled / Vcell)
in our case, drive = 1023 * (3.45 / 3.7) = 954
The drive parameters can be also fine tuned using an amp-meter in the high-power
LED circuit: adjust the drive until you reach the exact average current required for
your LED. Never set the drive under 80% of the maximum value."

[Forgetful Jedi Knight]

Always use a resistor!!!