Nuts and Volts - November 2013

The default 4 MHz clock speed for the microcontroller is more than adequate for measuring audible frequencies. By using a table of the established frequencies for musical notes, the result held in the W0 variable can be used to initiate some event such as lighting a designated LED or group of LEDs. We can use a list of the frequencies that make up the chromatic scale for any octave, such as the example shown in Table 1 used for the fourth octave scale. Using this list and with the help of a tone generator, you can compile an inventory of the translated numbers for each octave. For the list in Table 1, the translation would look something similar to this:

Note Frequency (Hz)

C4 261.63

C#4/Db4 277.18

D4 293.66

D#4/Eb4 311.13

E4 329.63

F4 349.23

F#4/Gb4 369.99

G4 392.00

G#4/Ab4 415.30

A4 440.00

A#4/Bb4 466.16

B4 493.88

■ FIGURE 8. Example of the frequency translation process.

Table 1. Frequencies of notes for the 4th Octave.

has translated values. You may want to double-check the calibration, especially if you make any modifications to the supplied schematics. The PULSIN frequency measurement command requires only three arguments which are the port or Pin# for the input, the State from which to measure from, and the Variable used to hold the value for the frequency. This command measures the length of a pulse on the input pin. Depending on the State variable, it either measures from the rising edge of the input or falling edge indicated by declaring a 0 or 1 value on the command line. The measured result is placed in the variable of choice. For example: C4 = 261 Hertz Translated value = 17

(beginning of the 4th Octave)

B4 = 493 Hertz Translated value = 37

(end of the 4th Octave)

PULSIN C.6, 1,  W0
 ; measure the low to high transitions on C.6
 ; & stores in W0

To light an LED or group of LEDs with a specific wavelength that includes a range of frequencies, you only need to provide a conditional IF/THEN statement for the range desired. The following is a code fragment that would cause the grouping of four yellow LEDs shown in the schematic to light if the sampled input frequency was between 260 and 493 Hz: EXAMPLE DISCRIMINATION FOR THE 4TH OCTAVE :

ITEM QTY DESCRIPTION SOURCE/PART#

BRD1 1 Proto Board Digi-Key V2009-ND BRD1 1 Proto Board Digi-Key V2025-ND

If W0 > 16 and W0 < 38 THEN
 ; any notes between 260Hz
 ; to 494Hz

SCKT1 1 20 Pin Socket Digi-Key A106188-ND SCKT2 2 18 Pin Socket Digi-Key ED3019-ND IC2, 3 2 ULN2803 Digi-Key ULN2803APG(ONHZA-ND) J1, 2 2 3.5mm Audio Digi-Key CP1-3543-ND

HIGH Y_UL,Y_UR,Y_LL,Y_LR : PAUSE
DELAY:LOW Y_UL,Y_UR,Y_LL,Y_LR
 ; light these 4 LEDS

Z1 1 2.7V Zener Diode Digi-Key 1N5223B-ND C2 2.01 µF Capacitor Digi-Key P4525TB-ND R1 1 10K 1/4W Resistor Digi-Key A105970CT-ND R2 1 22K 1/4W Resistor Digi-Key 22KAACT-ND R3 1 100 Ohm Resistor Digi-Key 10QBK-ND R4 1 10 Ohm Resistor Digi-Key 100DSCT-ND SP 4 1/2” Standoffs Digi-Key 3480K-ND PH 8 4-40 Screws Digi-Key 335-1082-ND D1-8 8 Green LED Digi-Key C4SMF-GJS-CV0Y0792TB-ND D9-14 6 Blue LED Digi-Key C503B-BCS-CV0Z0461-ND D15-18 4 Yellow LED Digi-Key 897-1071-ND

This IF/THEN statement lights the four LEDs connected to ports B.0-B. 3 if any notes within the fourth octave are sampled. You can go even further to enhance the effect of the translation of sound to light by carving up the octave into several patterns of yellow lighting.

D19-22 4 Pink LED Digi-Key 67-2062-ND D23 1 Red LED Digi-Key C503B-RBN-CW0Z0AA1-ND HDR1 1 40 Pin Male SIP SparkFun PRT-00116

We can accomplish this by lighting the upper left (Y_UL) and lower right (Y_LR)

HDR2 1 40 Pin Female SIP SparkFun PRT-00115

IC1 1 PICAXE 20M2 SparkFun COM-10807 BATT 1 4AAA Batt Holder RadioShack Cat# 270-411 HLDR 1 Document Holder Office Max SKU# 309264 MISC Shielded 2 conductor wires for audio connection.