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| Operational lifetime counter IC? |
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| mfarver:
Does anyone know of a IC that automatically does a "runtime hours" or powered on time counter? Or an "odometer on a chip" solution? Everything we log for maintenance purposes is based on operational time. I don't really need an RTC, and I can't put a battery into the design anyway. It isn't too hard to implement this using a small micro with some onboard EEPROM and a reasonably accurate onboard clock. Still it would be a great to be able to claim to management that there was a one chip/tamper resistant solution for this. Seems like this is something that should exist, but I haven't found anything. |
| N2IXK:
http://www.kep.com/productPages/counters-timers-ratemeters/K198-PCB-mount-hour-meter.html Back in the pre-ROHS days, the usual solution for this was a little gizmo called an "Indachron", which was a tiny capillary tube filled with mercury, with a little bubble that would slowly move along the length of the tube over the life of the device. A scale similar to a thermometer gave the runtime indication. These were used on a lot of industrial/broadcast gear subassemblies like VTR headwheels or large xenon arc lamps which required replacement after X number of hours of service, or which had pro-rated warranties based on service life before failure. A datasheet for these things is available here: http://datasheet.octopart.com/120PC12625-Curtis-Industries-datasheet-27869806.pdf , but due to the mercury content, the product line has apparently been discontinued. Some distributors still have them in stock, though. |
| nctnico:
A simple 8 pin microcontroller with internal EEPROM can do this. Be sure to write the EEPROM in a circular loop so you can enhance the lifetime of the eeprom. If you have the microcontroller transmit the run time counter as a UART serial format you only need to connect a UART interface to read the data (9600 baud can bet bit-banged so you don't need a real UART). |
| mfarver:
The subassemblies (which are field swappable) all report runtime back to a master diagnostic module so the counter needs to be digitally readable. |
| ajb:
A 6- or 8-pin micro would be a good solution, but may be problematic depending on how tamper proof you need it to be. While most micros have some provision for securing the program memory, I'm not sure what your options are for preventing the EEPROM from being erased. Usually you're trying to prevent data from being read from memory, but want to be able to erase it at will. You have the opposite problem. I think on an ATTiny13, for example, if you set the lock bits to mode 3 and set the EESAVE fuse that might do the trick--but it might still be possible to unlock and erase the EEPROM via high voltage programming if you have a really determined tamperer. |
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