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Last Chance Timer

This page is about a small hobby electronics project that I call Last Chance Timer (LCT), built from a few LEDs, and Atmel ATtiny44 microprossor, and a small plastic box I got on clearance at the local grocery store.

Overview

Jilian Michaels, one of the athletic trainers from Biggest Loser, has an exercise video called Last Chance Workout that takes you through intervals of a variety of cardio, strength, and fat burning routines. It packs a great workout into a short period of time, and luckily was available on the local cable company's on-demand offering for free. But how do you manage timing those intervals when you're on the road, or the cable is out, or GASP when the cable company removes the Last Chance from their on-demand lineup?

You build a little timer device, that's what you do!

Called the Last Chance Timer (LCT), this project is a small box that has a few buttons and LEDs to help keep track of interval durations. Since I've been away from electronics for a few years and am just dusting off the soldering iron, I'm keeping this project simple. The basic idea is a timer that keeps track of intervals, which are just periods of time (during which the operator is supposed to be doing exercise) with optional rest periods in between.

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Features

While it is still up to you to do the vigorous exercises and get out of breath and sweaty, you will be free from watching the clock and counting the seconds. Here's a list of the features:

• There are two modes of operation: Intervals and Setup. A slider switch will toggle between the two modes.
• There are two (2) LEDs of each color (green, yellow, red) totalling six (6) LEDs that behave differently depending upon the mode.
• Mode: Setup
  • When the mode selection switch is set to Setup, the top red LED will turn on solid as an indicator of Setup mode.
  • A momentary push button can be pressed to select between five (5) interval styles.
  • As the user presses the style selection button, one of the remaining five (5) LEDs will illuminate at a time, indicating which interval style the user is selecting.
• Mode: Intervals
  • The microcontroller will measure intervals of time. The duration depends upon the interval style selected when the system was in Setup mode.
  • As the interval progresses, the six (6) LEDs will illuminate one at a time to give the exerciser a visual indicator of the progress through the interval.
  • Once the interval is complete and all six (6) LEDs are illuminated, there will be a rest period (useful to allow the sweaty person to reposition for the next exercise, or to pick up hand weights, or move the yoga mat) during which all LEDs will flash in unison.
  • An audio tone will play at the completion of the interval as well, to allow the sweaty person to be on the floor doing pushups with no line of sight to the Last Chance Timer.
  • There is a slider switch to enable/disable the audio output, in the event that the user finds it annoying, or is practicing interval ninja training that requires silence.
  • Upon completion of the rest period, all LEDs will turn off and the process begins again.

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Interval Styles

The before the sweaty person becomes sweaty, they have the ability to select between five (5) pre-defined styles of interval. As of this writing, the firmware will only support four (4) styles, with the fifth being reserved for future use.

NOTE: This webpage is being written before the project is final. So far only coding done is proof of concept so that things can move on to PCB manufacturing. There is a nagging feeling in my mind that there will be issues with the size of the program code and the ATtiny44 flash program memory, so it is a deliberate design decision to keep the interval styles similar so the code can be reused between styles.

Style ID	Interval	Rest
1	30 sec	5 sec
2	30 sec	10 sec
3	45 sec	5 sec
4	45 sec	10 sec

You know you're a techie if you're upset that I began with index 1 rather than 0. Enjoy!

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Power Supply

The LCT is powered by 4 NiMH rechargable batteries, providing 6V DC. I have ambitions of including a very simple solar trickle charger to it, which will remove the need to charge the batteries. A sweaty person only needs to remember to set the device on a shelf by a window when done sweating.

The raw power from the batteries/solar cell is run through a ??? linear volatge regulator to provide a nice steady 5V DC to the microcontroller and other components. Reason for choosing this regulator? I have some. Makes the decision easy for this simple project for which I'm hoping to only use components that I have off the shelf, with no plan of spending additional money.