jackjack wrote:I just had two questions regarding the resistors required for Apple compatibility.
If 2v is required for the D+ and D- pins for 500mA charging, and the way to alter voltage at those pins with resistors can be calculated by V(out) = V(in) * (r1/(r1+r2)), then doing some algebra, we get 2=5 (r1/r1+r2), or 2/5 = r1/r1+r2. Solving, we essentially get r1=2 and r2=3, in essence, r2 = 1.5x r1.
My question is:
1. If r2 is 75k, then shouldn't r1 be 50k and not 49.9k?
2. Does that mean theoretically, we can use a 15k r2 and 10k r1?
Just for interest, I did get a 50k resistor (which were much easier to find than 49.9k) to try it out and can confirm that I could get an iPhone 4 charging.
Both data lines:
pin 2: 1.76v
Pin 3: 1.82v
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