Solved (Sorta) - Controlling Lutron Maestro dimmer only works 30% of the time

Other Hardware General Electronics
1

Hi, found the below code and attempted to apply it. I contacted Lutron and they sent me the following specs:
IR carrier Frequency 40.0 kHz
Duty Cycle 40%
Baud Rate 437 bps
Bit on time 10 usec, off time 15 usec

When I run the scrip the up command is processed about 30% of the time. So I assume much of the code is correct, but the processing by the dimmer is inconsistent. I suspect perhaps the baud rate but not sure how to set it or perhaps the duty cycle. I changed the pulse width from 2300 to 2200 and processing improved about 15%. Any other thoughts on how to proceed etc?
Thanks in advance
_Ernie

/* Control a Lutron Maestro light dimmer */
#define BIT_IS_SET(i, bits) (1 << i & bits)
// LED connected to digital pin 4
const int LED_PIN = 4;
// Width of a pulse, in microseconds 2200 is better than 2300
const int PULSE_WIDTH = 2200;
// # of bytes per command
const int COMMAND_LENGTH = 4;

const int UP[] = {255, 136, 130, 34};
const int DOWN[] = {255, 136, 130, 20};
const int ON[] = {255, 136, 132, 184};
const int OFF[] = {255, 136, 189, 18};
const int RECALL[] = {255, 136, 132, 183};

void setup()
{
pinMode(LED_PIN, OUTPUT);
}

/* Modulate pin at 39 kHz for give number of microseconds */
void on(int pin, int time) {
static const int period = 25;
// found wait_time by measuring with oscilloscope
static const int wait_time = 9;

for (time = time/period; time > 0; time--) {
digitalWrite(pin, HIGH);
delayMicroseconds(wait_time);
digitalWrite(pin, LOW);
delayMicroseconds(wait_time);
}
}

/* Leave pin off for time (given in microseconds) */
void off(int pin, int time) {
digitalWrite(pin, LOW);
delayMicroseconds(time);
}

/* Send a byte over the IR LED */
void send_byte(int bits) {
for (int i = 7; i >= 0; i--)
{
if (BIT_IS_SET(i, bits)) {
on(LED_PIN, PULSE_WIDTH);
} else {
off(LED_PIN, PULSE_WIDTH);
}
}
}

/* Send a full command /
void command(const int bytes[]) {
for (int i = 0; i < COMMAND_LENGTH; i++) {
send_byte(bytes);*

  • }*
    off(LED_PIN, 4 * PULSE_WIDTH);
    }
    void loop()
    {
  • command(UP);*
  • delay(2000);*
    }
2 
/* Send a full command */
void command( const int bytes[] ) 
{ for (int i = 0; i < COMMAND_LENGTH; i++) 
  {  send_byte(bytes);                                        <-----  bytes[i]  ???
  }
  off(LED_PIN, 4 * PULSE_WIDTH);
}

Do you have a scope/ logic analyser to take a peek at the signal ?.

This document might be good reference:
www.lutron.com/TechnicalDocumentLibrary/048158.doc

3

The timer 0 interrupt will be interfering with your timing. You need to:

  1. Stop generating the 40kHz by bit toggling and use one of the timers to generate it instead.

  2. For the PULSE_WIDTH delay, don't use delayMicroseconds, instead sit in a loop calling micros() until the required time since the start of the byte has elapsed.

Here is code I use to generate a fixed frequency on pin 9 of a Uno:

// Generate a square wave of a given frequency on the OCR1A pin

#define REQUIRED_FREQUENCY  (38000)
#define REQUIRED_DIVISOR ((F_CPU/REQUIRED_FREQUENCY)/2)

#if (REQUIRED_DIVISOR < 65536)
# define PRESCALER  (1)
# define PRESCALER_BITS  (1)
#elif (REQUIRED_DIVISOR < 8 * 65536)
# define PRESCALER  (8)
# define PRESCALER_BITS  (2)
#elif (REQUIRED_DIVISOR < 64 * 65536)
# define PRESCALER  (64)
# define PRESCALER_BITS  (3)
#elif (REQUIRED_DIVISOR < 256 * 65536)
# define PRESCALER  (256)
# define PRESCALER_BITS  (4)
#elif (REQUIRED_DIVISOR < 1024 * 65536)
# define PRESCALER  (1024)
# define PRESCALER_BITS  (5)
#else
# error Bad frequency
#endif

# define TOP        (((REQUIRED_DIVISOR + (PRESCALER/2))/PRESCALER) - 1)

void setup()
{
  pinMode(9, OUTPUT);
  digitalWrite(9, LOW);
  TCCR1A = 0;
  TCCR1B = (1 << WGM12) | PRESCALER_BITS;
  TCCR1C = 0;
  OCR1AH = (TOP >> 8);
  OCR1AL = (TOP & 0xFF);
}

void on()
{
  TCNT1H = 0;
  TCNT1L = 0;  
  TCCR1A = (1 << COM1A0);
}

void off()
{
  TCCR1A = 0;
}

void loop()
{
  // Generate a burst 2ms long, then wait 10ms before generating the next one
  on();
  delay(2);  
  off();
  delay(10);
}
4

Would it be possible to use the folowing while the IR bits are being send ?.
To disable interrupts: cli(); // disable global interrupts
and to enable them: sei(); // enable interrupts
Note that the millis timer, and serial communication will be affected by disabling interrupts. The delayMicroseconds() function disables interrupts while it is running.

5

Thanks I'll try these ideas tonight or tomorrow.
_Ernie

6

Problem solved - sorta. I gave up trying to send the proper codes with the proper carrier frequency, instead I hacked the Lutron remote. Connected two small wires, one to its ground and the other to the up tracings. I then short the two wires via an optocoupler (4n28) and fire it from the UNO. Works perfectly every time.
_Ernie