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authorbnewbold <bnewbold@robocracy.org>2012-12-24 04:18:04 +0100
committerbnewbold <bnewbold@robocracy.org>2012-12-24 04:18:04 +0100
commit2924a072d6799159f4d1d34e8d99d4bebb5e6826 (patch)
tree421aef1e6df61bd8406a87384ea016e56f3fc766
parent6285082776d9668f4663c36fbed571ad64d7fa0b (diff)
downloadbytetunes-2924a072d6799159f4d1d34e8d99d4bebb5e6826.zip
bytetunes-2924a072d6799159f4d1d34e8d99d4bebb5e6826.tar.gz
hardware notes
-rw-r--r--circuit.txt79
-rw-r--r--sine_lookup.c31
2 files changed, 110 insertions, 0 deletions
diff --git a/circuit.txt b/circuit.txt
new file mode 100644
index 0000000..1ad056e
--- /dev/null
+++ b/circuit.txt
@@ -0,0 +1,79 @@
+
+### Circuit
+
+http://www.uchobby.com/index.php/2008/01/08/arduino-audio-dac-options/
+
+ 47kohm resistor off pin, then 0.01uF cap to ground and speaker in parallel,
+ optionally with a pot or pair of resistors (sum=100khom?) acting as a
+ voltage divider for the headphones.
+
+### MCU configuration
+
+Set interrupt timer for 8KHz.
+
+Set PWM period to 255, prescaler to 1; this gives a period of 3.54
+microseconds, or about 282KHz. Further filtering may not even be needed?
+
+### Example Code
+
+#define PWM_OUT_PIN BOARD_LED_PIN
+
+HardwareTimer pwm(1);
+HardwareTimer gen(1);
+
+uint8_t[64] sine_lookup;
+int counter = 0;
+
+/*
+from math import sin
+count = 64
+print [int(127+127*sin(3.14159268*2*i/count)) for i in range(count)]
+*/
+unsigned char sine_lookup[] __FLASH__ = {127, 139, 151, 163, 175, 186, 197, 207, 216,
+ 225, 232, 239, 244, 248, 251, 253, 254, 253, 251, 248, 244, 239, 232, 225,
+ 216, 207, 197, 186, 175, 163, 151, 139, 126, 114, 102, 90, 78, 67, 56, 46,
+ 37, 28, 21, 14, 9, 5, 2, 0, 0, 0, 2, 5, 9, 14, 21, 28, 37, 46, 56, 67, 78,
+ 90, 102, 114};
+
+void setup() {
+ // configure PWM output
+ pinMode(PWM_OUT_PIN, OUTPUT);
+ pwm.setChannel1Mode(TIMER_PWM);
+ pwm.setPrescaleFactor(1);
+ pwm.setOverflow(255); // 8-bit resolution
+ pwm.setCompare(1, 128); // initialize to "zero"
+
+ // configure 8KHz ticker and interrupt handler
+ gen.pause();
+ gen.setPeriod(125); // 8Khz
+ gen.setChannel1Mode(TIMER_OUTPUT_COMPARE);
+ gen.refesh()
+
+
+ // get things started!
+ gen.resume()
+}
+
+void loop() {
+ // USB serial interaction code goes here...
+}
+
+void handler_sample(void) {
+ pwm.setCompare(1, sin_8bit(counter, 800)); // 100Hz sine wave
+ // pwm.setCompare(1, execute(counter);
+ counter++;
+}
+
+uint8_t sin_8bit(int counter, int period) {
+ int high, low;
+ float t = (t % period) / (float)period;
+ float weight = t - (t % 1);
+ low = sine_lookup[63*t];
+ if (63*t >= )
+ high = sine_lookup[0];
+ else
+ high = sine_lookup[1+63*t];
+
+ return (int)(low * weight + high * (1.0 - weight)):
+}
+
diff --git a/sine_lookup.c b/sine_lookup.c
new file mode 100644
index 0000000..1d12f76
--- /dev/null
+++ b/sine_lookup.c
@@ -0,0 +1,31 @@
+
+#include <stdio.h>
+
+
+unsigned char sine_lookup[] = {127, 139, 151, 163, 175, 186, 197, 207, 216,
+ 225, 232, 239, 244, 248, 251, 253, 254, 253, 251, 248, 244, 239, 232, 225,
+ 216, 207, 197, 186, 175, 163, 151, 139, 126, 114, 102, 90, 78, 67, 56, 46,
+ 37, 28, 21, 14, 9, 5, 2, 0, 0, 0, 2, 5, 9, 14, 21, 28, 37, 46, 56, 67, 78,
+ 90, 102, 114};
+
+unsigned char sin_8bit(int counter, int period);
+
+unsigned char sin_8bit(int counter, int period) {
+ int high, low;
+ float t = (counter % period) / (float)period;
+ float weight = (63*t) - (int)(63*t);
+ low = sine_lookup[(int)(63*t)];
+ if (63*t >= 62)
+ high = sine_lookup[0];
+ else
+ high = sine_lookup[1+(int)(63*t)];
+ //printf("\tl=%d h=%d w=%f\n", low, high, weight);
+ return (int)(high * weight + low * (1.0 - weight));
+}
+
+void main() {
+ int i;
+ for(i=0; i<800;i++){
+ printf("%d\t%d\n", i, sin_8bit(i, 800));
+ }
+}