Initial commit, working version

.gitignore

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+*.sublime-workspace
+.pioenvs/

TinyDimmer.sublime-project

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+{
+  "folders":
+  [
+    {
+      "path": ".",
+      "file_exclude_patterns": ["*.sublime-project"]
+    }
+  ]
+}

build.ps1

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+& platformio run

platformio.ini

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+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; http://docs.platformio.org/page/projectconf.html
+
+[env:attiny85]
+platform = atmelavr
+board = attiny85
+upload_protocol = stk500v1
+upload_flags = -P$UPLOAD_PORT -b$UPLOAD_SPEED
+board_f_cpu = 8000000L
+
+upload_port = COM7
+upload_speed = 19200

src/ledpwmcurve.c

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+#include <stdint.h>
+#include <avr/pgmspace.h>
+
+#include "ledpwmcurve.h"
+
+// Source: https://electronics.stackexchange.com/a/118120
+
+// Anti-Log (reverse) lookup table
+// y = 0-255 (pwm output), y_range=256
+// x = 0-1023 (10-bit ADC input);
+// assuming lower/higher end of ADC out values cannot be used
+// discarding first 32 and last 32 values.
+// min_x = 32, max_x = 1023-min_x, x_range=1024-2*min_x
+// ANTI_LOG[y] = round( x_range*log(y, base=y_range) + min_x )
+// given a value of x, perform a binary lookup on below table
+// takes about 28uS for Attiny85 @8MHz clock
+const uint16_t ANTI_LOG[] PROGMEM =
+{
+  0x0000, 0x0020, 0x0098, 0x00de, 0x0110, 0x0137, 0x0156, 0x0171, 0x0188, 0x019c, 0x01af, 0x01bf, 0x01ce, 0x01dc, 0x01e9, 0x01f5,
+  0x0200, 0x020a, 0x0214, 0x021e, 0x0227, 0x022f, 0x0237, 0x023f, 0x0246, 0x024d, 0x0254, 0x025b, 0x0261, 0x0267, 0x026d, 0x0273,
+  0x0278, 0x027d, 0x0282, 0x0288, 0x028c, 0x0291, 0x0296, 0x029a, 0x029f, 0x02a3, 0x02a7, 0x02ab, 0x02af, 0x02b3, 0x02b7, 0x02bb,
+  0x02be, 0x02c2, 0x02c5, 0x02c9, 0x02cc, 0x02cf, 0x02d3, 0x02d6, 0x02d9, 0x02dc, 0x02df, 0x02e2, 0x02e5, 0x02e8, 0x02eb, 0x02ed,
+  0x02f0, 0x02f3, 0x02f5, 0x02f8, 0x02fa, 0x02fd, 0x0300, 0x0302, 0x0304, 0x0307, 0x0309, 0x030b, 0x030e, 0x0310, 0x0312, 0x0314,
+  0x0317, 0x0319, 0x031b, 0x031d, 0x031f, 0x0321, 0x0323, 0x0325, 0x0327, 0x0329, 0x032b, 0x032d, 0x032f, 0x0331, 0x0333, 0x0334,
+  0x0336, 0x0338, 0x033a, 0x033c, 0x033d, 0x033f, 0x0341, 0x0342, 0x0344, 0x0346, 0x0347, 0x0349, 0x034b, 0x034c, 0x034e, 0x034f,
+  0x0351, 0x0352, 0x0354, 0x0355, 0x0357, 0x0358, 0x035a, 0x035b, 0x035d, 0x035e, 0x0360, 0x0361, 0x0363, 0x0364, 0x0365, 0x0367,
+  0x0368, 0x0369, 0x036b, 0x036c, 0x036d, 0x036f, 0x0370, 0x0371, 0x0372, 0x0374, 0x0375, 0x0376, 0x0378, 0x0379, 0x037a, 0x037b,
+  0x037c, 0x037e, 0x037f, 0x0380, 0x0381, 0x0382, 0x0383, 0x0385, 0x0386, 0x0387, 0x0388, 0x0389, 0x038a, 0x038b, 0x038c, 0x038e,
+  0x038f, 0x0390, 0x0391, 0x0392, 0x0393, 0x0394, 0x0395, 0x0396, 0x0397, 0x0398, 0x0399, 0x039a, 0x039b, 0x039c, 0x039d, 0x039e,
+  0x039f, 0x03a0, 0x03a1, 0x03a2, 0x03a3, 0x03a4, 0x03a5, 0x03a6, 0x03a7, 0x03a8, 0x03a9, 0x03aa, 0x03ab, 0x03ab, 0x03ac, 0x03ad,
+  0x03ae, 0x03af, 0x03b0, 0x03b1, 0x03b2, 0x03b3, 0x03b4, 0x03b4, 0x03b5, 0x03b6, 0x03b7, 0x03b8, 0x03b9, 0x03ba, 0x03ba, 0x03bb,
+  0x03bc, 0x03bd, 0x03be, 0x03bf, 0x03bf, 0x03c0, 0x03c1, 0x03c2, 0x03c3, 0x03c3, 0x03c4, 0x03c5, 0x03c6, 0x03c7, 0x03c7, 0x03c8,
+  0x03c9, 0x03ca, 0x03ca, 0x03cb, 0x03cc, 0x03cd, 0x03cd, 0x03ce, 0x03cf, 0x03d0, 0x03d0, 0x03d1, 0x03d2, 0x03d3, 0x03d3, 0x03d4,
+  0x03d5, 0x03d6, 0x03d6, 0x03d7, 0x03d8, 0x03d8, 0x03d9, 0x03da, 0x03db, 0x03db, 0x03dc, 0x03dd, 0x03dd, 0x03de, 0x03df, 0x03df
+};
+
+// Binary lookup using above table
+uint8_t antilog(uint16_t value)
+{
+  uint8_t result = 0x80;
+  uint16_t lookupValue;
+
+  for(uint16_t jumpOffset = 0x40; jumpOffset > 0; jumpOffset >>= 1)
+  {
+    lookupValue = pgm_read_word_near(ANTI_LOG + result);
+    if (lookupValue > value)
+    {
+      result -= jumpOffset;
+    }
+    else if (lookupValue < value)
+    {
+      result |= jumpOffset;
+    }
+    else
+    {
+      return result;
+    }
+  }
+
+  if (pgm_read_word_near(ANTI_LOG + result) > value)
+  {
+    result -= 1;
+  }
+
+  return result;
+}

src/ledpwmcurve.h

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+#ifndef __LEDPWMCurve
+#define __LEDPWMCurve
+
+extern uint8_t antilog(uint16_t value);
+
+#endif

src/main.c

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+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <avr/sleep.h>
+#include <util/delay.h>
+
+#include "ledpwmcurve.h"
+
+/*
+  Pin 2: 10k potentiometer input
+            When turned all the way to the left (off), resistance should be 0
+  Pin 5: PWM output
+*/
+
+
+// Forward declarations
+inline void initPWM();
+inline void initADC();
+inline uint16_t readADC();
+inline void sleep(uint8_t prescale);
+
+
+
+int main()
+{
+  // Set pin B0 (physical pin 5) to output mode, pin B2 (ADC1) to input
+  DDRB = (DDRB | _BV(DDB0)) & ~_BV(DDB3);
+
+  initPWM();
+  OCR0A = 255;
+
+  initADC();
+
+  while (1)
+  {
+    uint8_t value = 255 - antilog(readADC());
+    OCR0A = value;
+
+    if (value == 255)
+    {
+      // Off, go to sleep for 0.25s
+      sleep(_BV(WDP2));
+    }
+  }
+
+  return 0;
+}
+
+
+
+inline void initPWM()
+{
+  // Set timer to Fast PWM mode, clear OC0A on compare-match and set OC0A on top.
+  // This inverts the PWM, but allows the LEDs to turn off completely.
+  TCCR0A = _BV(COM0A1) | _BV(COM0A0) | _BV(WGM01) | _BV(WGM00);
+
+  // Leave WGM02 empty for Fast PWM mode, and set clock select to no prescaling
+  TCCR0B = _BV(CS00);
+
+  // Disable timer 1
+  TCCR1 = 0;
+}
+
+
+inline void initADC()
+{
+  // Use VCC as voltage reference and right adjust result,
+  // set to single-ended input on ADC1
+  ADMUX = (ADMUX | _BV(MUX0) | _BV(MUX1))
+                 & ~(_BV(MUX2) | _BV(MUX3) | _BV(REFS1) | _BV(REFS0) | _BV(ADLAR));
+
+  // Disable digital input on the analog pin to save power
+  DIDR0 |= _BV(ADC3D);
+
+  // Enable the ADC
+  ADCSRA |= _BV(ADEN) | _BV(ADPS1) | _BV(ADPS0);
+}
+
+
+inline uint16_t readADC()
+{
+  // Start conversion
+  ADCSRA |= _BV(ADSC);
+
+  // Wait for result
+  loop_until_bit_is_clear(ADCSRA, ADSC);
+
+  // ADCL must be read first
+  uint8_t low = ADCL;
+  return (ADCH<<8) | low;
+}
+
+
+inline void sleep(uint8_t prescaler)
+{
+  // Disable watchdog reset flag
+  MCUSR &= ~_BV(WDRF);
+
+  // Enable watchdog
+  WDTCR |= _BV(WDCE) | _BV(WDE);
+
+  // Set timeout value and enable interrupt mode
+  WDTCR = prescaler | _BV(WDIE);
+
+
+  // Turn ADC off
+  ADCSRA &= ~_BV(ADEN);
+  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
+
+  // Set sleep bit and halt the CPU
+  sleep_enable();
+  sei();
+  sleep_cpu();
+
+  // ...goooood morning!
+  cli();
+
+
+  // Disable watchdog (need to write a logic one first, see datasheet)
+  WDTCR |= _BV(WDCE) | _BV(WDE);
+  WDTCR = 0;
+
+
+  sleep_disable();
+  ADCSRA |= _BV(ADEN);
+
+  sei();
+}
+
+
+// Interrupt for watchdog timer
+ISR(WDT_vect)
+{
+}

upload.ps1

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+& platformio run --target upload