Meanwell LDD driver: for those who want to dim to 0 using Arduino

[Cintax]

I've looked at radio shack and all the resistor have a watt rating as well, 10kohm 1/2-1/4-1/8watt. Does that part matter?

 

According to the Amtel specification sheet the maximum current that could be drawn before failure of the GPIO is 40mA. To protect the GPIO you always need at least a 1kΩ resistor on the output.

 

To answer your question regarding the power rating on the resistors....

 

Our circuit diagram!

			 R1GPIO ------/\/\/\---------- LDD-H PWM Pin		   1kOhm	|					|	R2					|--/\/\/\-- GND					   10kOhm

 

V₁ = (R₁/R_t) * V_s = 5v * (1kΩ/11kΩ) = 0.45v (rounded)

 

You could use Kirchoffs voltage law to determine V₂ or you can use the voltage divider formula.

 

V₂ = V_s - V₁ = 5v - 0.45v = 4.55v

 

or

 

V₂ = (R₂/R_t) * Vs = 5v * (10kΩ/11kΩ) = 4.55v (rounded)

 

Now that we have the voltage drops across the resistors we can determine the current through this series circuit.

 

R_t = R₁ + R₂ = 1kΩ + 10kΩ = 11kΩ

I_t = V_s / R_t = 5v / 11kΩ = 454μA (0.454mA)

 

Calculating power using voltage and resistance:

 

P = V * I

P_t = V_s * I_t = 5v * 454μA = 2.27mW

P₁ = V₁ * I_t = 0.45v * 454μA = 205μW (0.2mW)

P₂= V₂ * I_t = 4.55v * 454μA = 2.06mW

P = P_t - (P₁ + P₂) = 2.27mW - (2.06mW + 205μW) ≈ 0.1mW (rounding error)

 

You could have solved it this way as well using current and resistance:

 

P = I²R

P_t = I²R_t = (454μA)² * 11kΩ = 2.27mW

P₁ = I²R₁ = (454μA)² * 1kΩ = 207μW

P₂ = I²R₂ = (454μA)² * 10kΩ = 2.06mW

P = P_t - (P₁ + P₂) = 2.27mW - (2.06mW + 207μW) ≈ 0

 

You will notice that values of P₁ and P₂ are way less than 125mW (1/8 W). This means you can safely use a 1/8W resistor for both R₁ and R₂.

 

 

 

TL;DR: Any resistor with a wattage rating greater than or equal to 1/8 W will be fine.

[bored4]

Wow! thanks alot going through all the math and explaining it all.

[zemuss]

So this power supply you can hook up multiple drives to it right? If so it just shaved about 40 dollars off my build price.

[MOJOEJOEJOE]

Im still using a power mosfet as my driver because of the fact that it has 4 outputs in one package. Im also using a power supply from an old pc and running everything off of 12 vdc. I love the contoller though. Did you write the code yourself for the touch screen? I was thinking about getting one but all my code is simple analog writes nothing fancy.LOL.