I'm looking to create a circuit in a somewhat small package to fit inside a power tool that would track how many times it was plugged in or had its trigger activated. Any method of reviewing the count is fine (prefferably inexpensive). I'm a novice in electronics, and so I'm looking for some help in a general design.
You will want a small microcontroller and a bit of flash memory, either internal to the processor (if it can self-program) or as an external chip probably with a synchronous serial interface.
You will need to write a logging routine compatible with the byte write but sector erase nature of flash memory. Probably you would do something like write a running count filling up the memory, and erasing the oldest sectors as you come close to running out of space. When you want to determine the count, you search the memory for the latest data.
For reporting, you have to decide if you want to add a connector for a "computer" to read out the usage (a logic level serial port is probably simplest) or if you want a human to determine the count without added tools. For human interface, you could do something like morse code or beep count with a little buzzer inside, though you have to have some way of triggering that. Getting fancier with readout tools, you can go through the case plastic with an ultrasonic transducer, or modulate a data signal onto the charging jack, etc - but these are not simple.
If only a few units are to be made, development cost dominates so convenient to program parts (seperate processor and SPI flash) may make the most sense. With a lot of units, their unit cost dominates and you will want to try to get everything in one small IC.
Would this be a good project for a PIC microcontroller? As far as the count readout, human readable is fine, so I'll look at what you suggested in more detail. Would morse code be easiest to implement?
The meter would need to be enclosed in the case, so there wouldn't be much room, except for maybe a micro controller along with supporting components. Can you give me an example of what your suggesting?
Err, no. A commercial power meter, that is used to check the energy usage of appliances, available for the equivalent of $10us or so. It plugs into the socket, and the power tool/whatever plugs into it.
Hi Dirk. I was afraid of that idea coming across this thread. In reality, I'm known in my hometown for the power tools, and people always borrow them without returning them promptly as promised. So, I thought it would be to see how much people are actually using them :). I suspect one neighbor is using my tools on the job somewhere. I dunno... kinda bugs me out. :)
You're not onto a bad idea there... next thing you'll see at home depot is rental charges based on the usage cycles, heh ;)