I am currently designer a battery voltage tester using a PIC16F818. I plan on running the circuit off a 9V battery that is connected to a 7805 to provide 5V to the PIC.
The batteries that need testing have a maximum voltage of 9V. However since only a maximum of 5V can be applied to any of the PICs pins I have the battery being tested hooked up to a voltage divider which then connects to on of the A/D pins and will compensate for this voltage divide in the source code.
I was going to connect the PIC in between the two resistors of the voltage divider. Also I was going to have both resistors of the voltage divider to be the same value so the voltage is halved. However since the PIC will be connected in between the two resistors, this will make the PIC and second resistor be in parelle causing the voltage not to be halved. I need to know what the resistance of the PIC pins are so that I can compensate for this extra resistance.
1. Am I correct that the PIC and R2 would be in parelle cause the voltage not to be halved?
2. If so, what is the resistance of the PIC so that I can change the values of R1 and R2 so that the voltage of the battery being tested is halved?
+ Test Battery
|
R1
|
|----------------PIC A/D Pin
|
R2
|
GND
The batteries that need testing have a maximum voltage of 9V. However since only a maximum of 5V can be applied to any of the PICs pins I have the battery being tested hooked up to a voltage divider which then connects to on of the A/D pins and will compensate for this voltage divide in the source code.
I was going to connect the PIC in between the two resistors of the voltage divider. Also I was going to have both resistors of the voltage divider to be the same value so the voltage is halved. However since the PIC will be connected in between the two resistors, this will make the PIC and second resistor be in parelle causing the voltage not to be halved. I need to know what the resistance of the PIC pins are so that I can compensate for this extra resistance.
1. Am I correct that the PIC and R2 would be in parelle cause the voltage not to be halved?
2. If so, what is the resistance of the PIC so that I can change the values of R1 and R2 so that the voltage of the battery being tested is halved?
+ Test Battery
|
R1
|
|----------------PIC A/D Pin
|
R2
|
GND