|
This project might be interesting to you if you're trying to interface an analog (e.g. resistance or voltage controlled synth) to a microcontroller, perhaps to drive the synth via MIDI....
The basic circuit is a 40106 oscillator comprising 40106 (Hex Inverter), 0.1uF capacitor, 100K potentiometer and 5V power supply. I am playing mine through an external amplifier. See http://hackaday.com/2008/05/01/how-to-make-a-digital-synthesizer/ for ideas on building the basic oscillator
To make it play a tune, I replaced the 100K potentiometer with an Analog Devices AD5242BRZ100 digital potentiometer. At the time I could only get the SOP16 surface mount component and had to use an adaptor board (nightmare!). Still, its a natty little IC. Here it is, crudely (and painfully) soldered onto the adaptor
 This is a dual digi-pot which can dial up 2 separate resistances between 0-100K on a granularity of 256 graduations, so pitch translation is not going to be perfect :)
You communicate with the digi-pot via I2C serial link. I drove it from an Arduino clone using the Arduino "wire" library which makes this whole process pretty easy. First off though, here is how I wired up the digi-pot
On the Arduino the code to play the tune is as follows
#include <Wire.h>
void setup() { Wire.begin(); // join i2c bus } // These are the digi-pot resistor values (0-255) that I worked out
// correspond to each note byte note[25] = { 60, // C 0 75, // 1 87, // D 2 93, // 3 105, // E 4 115, // F 5 124, // 6 130, // G 7 139, // 8 144, // A 9 151, // 10 157, // B 11 163, // C 12 167, // 13 173, // D 14 177, // 15 184, // E 16 188, // F 17 191, // 18 195, // G 19 199, // 20 202, // A 21 205, // 22 208, // B 23 211 // C 24 }; // this is the captain pugwash tun in note values (0-24). Pauses not currently supported!
byte tune[] = { 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 19, 16, 16, 12, 16, 16, 19, 24, 24, 19, 16, 16, 12, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 14, 11, 11, 7, 11, 11, 14, 17, 17, 14, 11, 11, 7, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 19, 16, 16, 12, 16, 16, 19, 24, 24, 19, 16, 16, 12, 12, 12, 24, 23, 23, 21, 19, 19, 17, 16, 16, 14, 12, 12, 12, 16, 16, 16, 12, 12, 12, 16, 16, 17, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 21, 21, 23, 24, 24, 23, 21, 21, 19, 17, 17, 16, 14, 14, 16, 17, 17, 16, 14, 14, 7, 9, 9, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 24, 23, 23, 21, 19, 19, 17, 16, 16, 14, 12, 12, 12, 16, 16, 16, 12, 12, 12, 12, 12, 12, 12, 12 } ; // This is the I2C identifier for a digi-pot with AD0=0 and AD1=0
#define POT00 0b0101100 byte i=0; void loop() { // get the current note number byte j = tune[i]; // Send out the I2C packed to the digital potentiometer Wire.beginTransmission(POT00); // transmit to device Wire.send(0b10000000); // sends instruction byte Wire.send(note[j]); // sends potentiometer value byte Wire.endTransmission(); // stop transmitting // step to next note
if(++i >= sizeof tune) i=0; delay(100); } Note that the digi-pot resistance values in the note[] array might need to be "tuned" if your 40106 oscillator plays different to mine... I worked these out by varying the resistance while I played each note of a scale on an electronic keyboard. I picked out note values that were approximately in tune with each key.. its always going to be a bit approximate anyway with the discrete steps used by the digi-pot
Here is a photo of the full circuit. The Arduino clone is one of Tom Scarff's MIDUINO boards. I am running the 40106 on an external 5V desktop supply.
 |