Nuts and Volts - November 2013

the octave to light all four lights, it creates a very interesting effect. It helps to assign names for the ports that is indicative of their physical locations. This same technique can be used to indicate when notes from the other octaves are played.

Using LEDs of the same color arranged in various patterns creates another interesting effect. I find that by using enough LEDs to make square, diagona,l or cross patterns can produce the best effects with the least number of LEDs. The layout of LEDs shown in Figure 2 is an example of this suggested arrangement. The software that is available for download was written expressly for the arrangement of diodes shown in Figure 5. The code has been well documented and should serve as a starting point for a layout of your own design. This design can be scaled up using several methods. One method to free up I/O lines would be to hard wire the LED patterns. This would allow you to have more patterns. Another method would be to connect more LEDs in parallel to the existing I/O lines. Each ULN2803 is rated up to 500 mA.

The duration for how long the LED is kept open during operation is controlled by the value held in the

DELAY variable. In the program listing provided, the DELAY is set to 50 milliseconds, but you may want to use different delay times for the ranges of the discriminated frequencies. There can be a noticeable difference using longer on times for higher frequencies, and shorter times for the lower frequencies.

Final Thoughts

This circuit is a single channel or mono design, so the choice of using the left or right channel is up to you. A stereo circuit may require more than just another input due to the time needed for both sampling and processing the results. A twin circuit would be ideal to produce a stereo effect. A sensitive microphone can be used as an input to the processor, as long as an amplifier is included to boost the signal. An alternative to using a separate board for the driver would be to mount the components directly to the back side of the display board. The 4” x 6” board for this project is a plated through hole design which would allow the parts to mount on either side. If you prefer that kind of design, feel free to email me if you need help with that implementation.