does Arduino Mega2560 (based on ATMega 2560) has an input pull-up on analog inputs? Can I set the input pull-up as usual by software?
The reason is that I need to use the analog pins as extra digital inputs.
Electronic – Arduino Mega Pull-up on Analog input
arduinopullup
Related Solutions
Input voltages can be "scaled" down to suit the Arduino's ADC input voltage range.
As Oli says, a 10V input can be scaled down with a potential divider.
In its most basic form this can be two resistors.
As shown below, the input current flows through R1 and through R2.
Voltage drop across a resistor = V = I x R
As both resistors carry identical current (= input current)
the voltage drop across each resistor is proportional to the resistor value
So, if R1 = R2 then the the voltage across each is equal so they each drop half the input voltage.
In the general case - input voltage is across R1+R2. Output voltage is across R2 only. So Vout = Vin x R2 / (R1 + R2)
ie the division ratio = R2 / (R1 + R2)
When R1 = R2 the division ratio is 1/2 so
a 0-10V input will be reduced to o-5 volts.
R1 and R2 can be typically 10k ohms each in this case.
Much larger values can be used but they can affect the conversion accuracy. eg 100k + 100k.
Usually it is wise to limit R2 to not more than about 20k ohm.
You will need the arduino ADK shield
http://www.emartee.com/product/42089/Arduino%20ADK%20Shield%20For%20Android
This works with all kinds of arduinoes :)
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Best Answer
A pull up makes no sense on an analog input.
The Atmega 2560 datasheet ADC section(page 268) makes no mention of pull ups on the analog inputs.
The digital section (page 67) shows the switchable pull ups.