Arduino Voltage Sense Help

[challen908]

Hey all,

I need some help, I have a board that runs off a 12V batter and is supposed to sense a car pedal throttle voltage. I have one signal line from the throttle and as the pedal pushes down the voltage on this sense line rises. I have fed this line straight into an Arduino Nano every analog pin and Arduino code will trigger a digital pin at specified voltages between 0.25V and 0.6V, anything outside that range needs to be shut off.

The problem is that when I connect the sense line to the A0 pin of the Arduino I get voltage drop on the sense line itself. For example the sense could be 0.4V and once its connected to the Arduino its drops to 0.25V. How can I prevent this, I can't have any, or next to none voltage drop on the sense line?

I can upload a schematic but the sense line is straight into A0 pin, Arduino is powering from 12V step down just fine

[challen908]

Do I need an op-amp or something to amplify the sense signal? I would like to keep the Arduino so that I can change the range of voltages I want to trigger and read the signal

[challen908]

[challen908]

based on the schematic the comparator is not connected, and assume the VIN goes right into the A0 pin on the Arduino with only a pull down 8.25k resistor

[ozcar]

Do you know how the VIN voltage is produced?

You could try it without the 8.25k pull down resistor, or see what effect a resistor to ground alone has on VIN.

Assuming nothing silly like programming the A0 pin as a digital output set low.

[challen908]

Yeah nothing silly in programming, and the VIN is coming from the vehicle, going through a potentiometer, and is LVDS, based on my customer’s info, he’s being really vague with me on the source