Arduino input signal

I have an Arduino UNO reading inputs from a gyroscope through an I^2C analog interface, then providing digital and PWM outputs to a motor driver that controls a dc motor. I have this control system working great, but would like to have electrical inputs that engage and disengage the system.

This is all taking place within a fairly large rocket. Before we load it onto the launch pad we must turn on the arduino/DC motor circuit by connecting two relatively large wires we cannot access from the launch pad. We would not like the arduino to engage sending signals to the motor driver until we close a 'signal' circuit by connecting two small wires sticking out of the rocket that we can access before shoving it in the rocket.

We have access to a 11.1V battery that could serve as the voltage source for this 'signal' circuit to engage the program. I can program everything myself, the problem I am having is with the arduino recognizing input signals. When I put the positive end of a 9V battery into a digital pin that I've designated as input, the arduino refuses to read that as a digital high signal. I have also tried reading it from an analog input and it also sees no difference. I have also tried this with the battery actually as part of a closed circuit and still see no input difference from the arduino.

Can you give me any tips on how to make the arduino read a signal coming from an 11.1V battery? If any resistors are needed?

Thanks, sorry for being vague, I can give more information as you need it.

WARNING - You can potentially damage the Arduino if you input more than 5V.

Just so I understand, you simply need a "start" signal of some kind? I'm afraid I'm misunderstanding you, since that's a LOT easier than the I^2C & PWM stuff..... Triggering an input ain't "rocket surgery"! :smiley: :smiley: :smiley:

The simplest approach would be to enable the internal pull-up resistor. (With the pull-up enabled, the input will read high when there is no connection to the input pin.) Then connect the input to Arduino's ground and the input will read low. You can use a switch or relay to make contact with ground. (Use that low signal to enable/trigger your event.) No external battery or other power source is required.

When I put the positive end of a 9V battery into a digital pin that I've designated as input, the arduino refuses to read that as a digital high signal.

(Ignoring the fact that you're exceeding the 5V limit... The voltage has to be postive relative to the Arduino's ground. (The negative side of the battery needs to be connected to ground.)