saving variables when stamp is not powered

Comments

• Chris Savage Parallax Engineering Posts: 14,406

  2007-08-23 15:57 edited 2007-08-23 15:57

  David,
  
  The only non-volatile memory on the BASIC Stamp is the EEPROM, however, if you keep updating a location within a loop like that you will eventually wear it out. If you had some battery-backed external RAM (Such as that commonly found on RTC chips) then you could save it to that every iteration of the loop. Take care.
  
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  Chris Savage
  Parallax Tech Support
• kelvin james Posts: 531

  2007-08-23 17:09 edited 2007-08-23 17:09

  You could use a " save button ", a button switch that would run a subroutine to write the value to eeprom, before you turn it off. You would read that value back at the beginning of the program, when the stamp is powered up again. I can't think of any way to do it automatically. You could also add a button to reset the variable to the original value if needed.
• Chris Savage Parallax Engineering Posts: 14,406

  2007-08-23 17:12 edited 2007-08-23 17:12

  It could be done automatically if it weren’t for the write speed of the EEPROM. Even with that I suppose if you had a custom power supply with large caps you could detect the loss of the AC mains and quickly store the data. The problem is that since you’re using a PAUSE you could be stuck there and miss the signal. Take care.
  
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  Chris Savage
  Parallax Tech Support
• dwbowen Posts: 30

  2007-08-26 01:06 edited 2007-08-26 01:06

  Thanks Guys,
  
  So I assume using the basic stamp's EEPROM involves using the READ and WRIGHT commands. Because I found I way to do what I needed to with those commands by writing, reading and rewriting the variable on two of the controllers pins. Chris, will doing this shorten the life of the controller or just the two pins? If so how many cycles do you think I can get before the thing quits working? The reason I ask is because the program sample I sent earlier was just a snippet of a much larger routine. This routine could cycle through every minute or it could cycle through in an hour or more. It is dependent on the movements of houseflies combined with the movements of people as they walk throughout a space and therefore extremely random. I'm in a time crunch (the exhibition goes up next week) and there are still many logistics to work out aside from this. I fear I do not have time to order and learn how to incorporate a battery/memory backup like you guys suggest. If the controller will not stand up the writing and rewriting on the pins I will probably just make sure it stays on all of the time.
  
  Thanks again,
  
  david
• Mike Green Posts: 23,101

  2007-08-26 02:02 edited 2007-08-26 02:02

  READ and WRITE don't involve any of the controller pins, they simply use the on-Stamp EEPROM. A "page" in EEPROM, usually a block of 64 bytes, can be rewritten somewhere on the order of 1,000,000 times. The EEPROM fails by being unable to write zero bits into a location. One way to help reduce the wear on a location is to use READ to read the location before writing and skip the WRITE if the value you want is already written there.
• Ol' Geo Posts: 30

  2007-08-26 04:56 edited 2007-08-26 04:56

  Can't you just add a pushbutton that would store the last count unto EEPROM by using WRITE command? Press the button just before you turn the power off. The stored datum occurs only once each time you turn the power off, hereby, it would not "wore out" the rom.
  
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  Ol' Geo
  Retired Software Engineer
  
  An oscilloscope is a window of unseen electronic world. - GM