Hi everyone,
so I've been wondering if there is a way to make a hidden button on a device (device wokring with ardunino) that will (once pressed) render the code useless - for example to delete values (val1, val2 ...) or in any way destroy the program that runs that device.
Any ideas?
Thanks,
Lubo (Bo)
Here's an idea:
when the button is pressed, you could just write all the values to 0 (or anything else, if you're trying to confuse the user by giving bogus readings), and put the chip in a never ending loop by using something like this:
while(1)
{
//do nothing here, or maybe keep clearing the values if you want
}
However, the code would start working again when you reset it, or of you power it off and then on again.
What is this mysterious feature for anyway?
One option I can think of (easy way out, no code) is to use a simple SPDT switch to connect the reset pin to ground (that way the micro can't do anything until you open the switch again), but this might not be suited to your (let's be honest, slightly dubious 
) purposes. If the switch is hidden well enough, then whoever it's hidden from might not have a clue as to what's going on, unless they're familiar with microcontrollers and have really sharp eyes.
Using the EEPROM to store variables seems a little overkill to me, unless for some reason you want them to be kept after you turn off the chip.
If you want a way to permanently destroy all the code on the chip until it's reprogrammed, it get's a little more complex...
If you're competent in programming in assembly, maybe you could somehow load the code into the RAM and go from there. This way, the code will vanish once the chip is powered off or reset. This seems like a daunting task to me, and forget using the Arduino environment to do this!
Or you could just set fire to the thing, whatever works best 
interesting ideas . Anyway i need it becouse im making a racing simulator (http://www.youtube.com/watch?v=y9m--orp8O8) and the idea is to put it in a gaming club (i've talked to the owner and its all good), now i know the guy , but its never bad to have a "dead man's switch" in case he decides to pull any stunts i can just "render the sim uselses" and gain leverage (im also putting a non-resetable timer in it to keep track at the time it was working)
In other words im just trying to cover all the angles here
it uses a teensy 3.0 (arduino doesnt have a joystick function) but its programed in the arduino IDE
i like the idea with the reset pit or a switch keeping the values at 0...i will keep thinking and see whats the best option (maybe all of them)
I was wondering if there is a way to irreversibly change a value to 0 or something similar so that once pressed the button ruins the code and it has to be reuploaded to the teensy
Yeah, you have 1K of internal EEPROM to mess around with, and it's dead easy to control with Arduino. You can do what Nico suggested and make the thing check for the important variable first before executing the never ending loop. Something like this (pseudocode, ceebs to write the real thing):
//burn this program to the Arduino first
void setup()
{
//write, say, the number 123 to eeprom adress 7 (completely arbitrary numbers I chose)
}
void loop()
{
//nothing to do here
}
//then erase that old program and write this new one
void setup()
{
//whatever your normal code would require in the setup goes here
}
void loop()
{
while(eeprom adress 7 == 123)
{
//work properly
if(secret button pressed)
{
//clear EEPROM address 7
}
}
lcd.print ("don't mess with a programmer");
}
I just thought of this code off the top of my head, I'm sure you can make it more efficient, maybe by using interrupts or something. No need for a keypad system or anything, unless you really want some password feature built into it. To reprogram the chip just pull it out of the DIP socket and stick it in your Arduino board, or include an ISP header in your design.
Really cool project btw, hope it all goes well 
