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)
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 
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
Thanks Mark, that's good to know. I had done a quick search and I must've gotten something outdated or just wrong 
So that would mean dirtdiver would just need a separate sketch to clear the one memory address he is using as the flag.
Interesting point about the legal side of it. I once put a time limit on a custom app, requiring a typed-in key to unlock it, and I'm pretty sure I would not have gotten paid without it!
dirtdiver, In terms of the number of writes available, you would only write the one memory location once per self-destruct button press. Or if the trigger is time related I suppose you could check it before writing so you don't re-write it unnecessarily.
Don't patent it!
I tell you, it's a waste of time, money and effort. You need to pay thousands of dollars, and here's the worst part: you have to publish a detailed description of your product and how it works! You're just making it a hundred times easier for some el-cheapo manufacturer to copy it! They won't care if you have a patent. If you do decide to sue someone over copying it, then that's going to set you back quite a bit for a lawyer! There's no way, even if you win, that you'll get that much money back from the patent.
If you decide to sell it (perhaps on a large scale) then there are precautions you can take to stop people from copying it. For example, you could get a custom PCB built for it, and sandpaper off all the markings on the ICs. If and when you decide to go big, then maybe a patent might be feasable. Also, if you don't really care about the money, and just want to get recognised, a patent might be a good idea, even now. Just know that you'll be paying a LOT of money for it. Think of how many goodies you can get on this website for $5000!
---
Also, @Sunil, the EEPROM method may not necessarily be the best way. In fact, there may not be a 'best' way at all. It's one way of doing things, and it seems feasable. It all depends on what the kill switch is for, how much effort you are willing to go to write the code, how good you are at coding, your time constraints, etc, etc, etc. This kill switch idea is good, but I can see it causing some disputes. A dedicated self destruct button will tick off the club owner much more than a simple discreet reset switch (which by the way, is not analogue as you mentioned before - analogue refers to a range of voltages in this case, the reset switch still uses digital logic), and you can still use the switch for leverage. Just tell the guy you need to take it for 'servicing' and secretly flip the switch while pretending to calibrate stuff, and give him a long technincal explanation as to why it went bust, like "the internal temperature of the dual H-bridge stepper driver rose too far beyond the nominal". He won't know you designed it for leverage (which I'm sure will make him mad and ruin the partnership), but he will know that only you can fix it, which gives you the leverage. Also it requires no extra coding. In addition to this, constantly checking the EEPROM might be quite taxing to the microcontroller, especially since it's doing a LOT of other work - this simulator is pretty complex! You might find that it decreases performance. This might be in the form of jittery servos for example - even with simple programs, if the MCU is checking constantly for, say, a timer value, then the servo just freaks out and goes all over the place! You could optimise this out using interrupts and all that but that just adds to the complexity of your program!
Again, this is also just one way of doing things. It may or may not be better than the EEPROM method, but it's up to dirtdriver to decide 
Yeah, thats what i heard about the patenting too, so its out of the game,
also im not worried about reverse engineering couse all they are going to see is the teensy the code in it cant be extracted as far as I know (it can but it will be all messed up and not full- it will be pretty useles)
I have a friend lawyer, i will talkmto him about a shor contract declaring that i have rights over the simulator or something similar i dont know yet .
Im not a good programer,as you can see from the simulator i dont have that kind of money to fool around with 
, i dont have much time,I will try the EEPROM (at least for the educational purpose of it , but if it slows down the program, then i wont use it)
