Nuts and Volts - October 2010

once you see what’s underneath you’ll see that it is not as scary as it seems at first blush.

There are two loops: the first sets up initial values; the second runs the active flicker algorithm. Most of the variables used by the flicker() method are local, but you’ll see that it uses the external level array and the leds object to control the wicks without further intervention by us. The code also accesses the (global) flickerdelay variable which affects the speed of wick movement.

At the top, a local random variable (lotto) is initialized and a loop runs which sets the base value of each wick to zero — the target in the upper range — and then randomizes the ramp control. The direction bits are cleared to zero which indicates that each wick is initially ramping up.

Now for the fun. At the start of each loop iteration, the value in lotto is re-randomized so that it’s always changing. For each wick, we decrement the ramp value and when that hits zero we increment or decrement the base value so that it moves toward the target. Once the target is reached, a new (random) target is generated.

Whenever a wick brightess is modified, the new level is set in the leds object. Note the use of the global level array which acts as an overall brightness control value. As we modify the level array in the main cog, it is used by the flame cog. I think this is really cool.

Overall loop speed is dictated by the number of

■ FIGURE 12. Jack in action.

active wicks and the value in flickerdelay. As we saw in the main code, we can change flickerdelay to alter the apparent behavior of the wicks. You’ll see there is just a bit of math before the waitcnt command — this is needed to prevent waitcnt from hanging (delay of about 56 seconds) when we have a small value in flickerdelay.

This process could be duplicated in another micro but I believe it would be a much bigger coding challenge.

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