According to the following circuit analysis to calculate the resistance value R1 corresponding to R12.
Requirements are as follows: the output current of 1uA; output voltage is 3V.
Calculated:
between the partial pressure of R1 and R2, R3 acting as a flow restrictor, when the microcontroller reads the I / O belonging to high impedance state, R3 equivalent circuit, considering R1, R2 can.
First, according to the partial pressure of the formula: Ur1-r2 = V1xR2 / ( R1 + R2)
current Ir1-r2 = V1 / (R1 + R2) = 1uA
according to claim i.e. V1 = Ur1-r2 = 3V calculating i.e. R2 = 3R1;
and from current calculating R1 = 3000K can be calculated from R2 = 9000K.
R1 is selected 3M 9.1M selected resistor to resistor R2.
