The other day my Arduino Mega knock-off arrived. I have a bunch of Arduino Nanos, but a project I'm looking into needs a lot more I/O. The Mega sports 56 I/O pins and will do nicely. Today I hooked up a relay board to give the setup a test. The Mega can drive the relays directly but I'm concerned they may draw too more current than the chip wants to provide. So I think I am going to play it safe and use an external supply to drive the relays. I ran some code that switched the relays just to hear them react. Initially I ran a binary count. I didn't feel like spiking the current and decided to run a
to the relay output. Gray code keeps makes sure only one bit (or relay) changes at a time. That's nice but still causes the first relay to clatter the most. I wanted something that would make all the relays turn on and off the same number of times throughout the count. I found
and that did the trick. This setup isn't useful to me, but it was kind of a cool experiment. Here is the code:
// 8-bit balanced gray code table.
// Copied from: http://gary-williams.livejournal.com/16275.html
uint8_t const GRAY_CODE[ 0x100 ] =
{
0x00, 0x01, 0x03, 0x02, 0x06, 0x0E, 0x0A, 0x0B, 0x09, 0x0D, 0x0F, 0x07, 0x05, 0x04, 0x0C, 0x08,
0x18, 0x1C, 0x14, 0x15, 0x17, 0x1F, 0x3F, 0x37, 0x35, 0x34, 0x3C, 0x38, 0x28, 0x2C, 0x24, 0x25,
0x27, 0x2F, 0x2D, 0x29, 0x39, 0x3D, 0x1D, 0x19, 0x1B, 0x3B, 0x2B, 0x2A, 0x3A, 0x1A, 0x1E, 0x16,
0x36, 0x3E, 0x2E, 0x26, 0x22, 0x32, 0x12, 0x13, 0x33, 0x23, 0x21, 0x31, 0x11, 0x10, 0x30, 0x20,
0x60, 0x70, 0x50, 0x51, 0x71, 0x61, 0x63, 0x73, 0x53, 0x52, 0x72, 0x62, 0x66, 0x6E, 0x7E, 0x76,
0x56, 0x5E, 0x5A, 0x7A, 0x6A, 0x6B, 0xEB, 0xEA, 0xFA, 0xDA, 0xDE, 0xD6, 0xF6, 0xFE, 0xEE, 0xE6,
0xE2, 0xF2, 0xD2, 0xD3, 0xF3, 0xE3, 0xE1, 0xF1, 0xD1, 0xD0, 0xF0, 0xE0, 0xA0, 0xB0, 0x90, 0x91,
0xB1, 0xA1, 0xA3, 0xB3, 0x93, 0x92, 0xB2, 0xA2, 0xA6, 0xAE, 0xBE, 0xB6, 0x96, 0x9E, 0x9A, 0xBA,
0xAA, 0xAB, 0xBB, 0x9B, 0x99, 0x9D, 0xDD, 0xD9, 0xDB, 0xFB, 0x7B, 0x5B, 0x59, 0x5D, 0x7D, 0x79,
0xF9, 0xFD, 0xBD, 0xB9, 0xA9, 0xE9, 0x69, 0x6D, 0x6F, 0x67, 0x65, 0x64, 0xE4, 0xE5, 0xE7, 0xEF,
0xED, 0xAD, 0xAF, 0xA7, 0xA5, 0xA4, 0xAC, 0xEC, 0x6C, 0x68, 0xE8, 0xA8, 0xB8, 0xF8, 0x78, 0x7C,
0xFC, 0xBC, 0xB4, 0xB5, 0xB7, 0xF7, 0xF5, 0xF4, 0x74, 0x75, 0x77, 0x7F, 0xFF, 0xBF, 0x9F, 0xDF,
0x5F, 0x57, 0x55, 0x54, 0xD4, 0xD5, 0xD7, 0x97, 0x95, 0x94, 0x9C, 0xDC, 0x5C, 0x58, 0xD8, 0x98,
0x88, 0xC8, 0x48, 0x4C, 0xCC, 0x8C, 0x84, 0xC4, 0x44, 0x45, 0xC5, 0x85, 0x87, 0xC7, 0x47, 0x4F,
0xCF, 0x8F, 0x8D, 0xCD, 0x4D, 0x49, 0xC9, 0x89, 0x8B, 0xCB, 0x4B, 0x4A, 0xCA, 0x8A, 0x8E, 0xCE,
0x4E, 0x46, 0xC6, 0x86, 0x82, 0xC2, 0x42, 0x43, 0xC3, 0x83, 0x81, 0xC1, 0x41, 0x40, 0xC0, 0x80
};
// LED pin.
enum { LED_PIN = 13 };
void setup()
{
pinMode( LED_PIN, OUTPUT );
// Set all I/O on port F as outputs.
DDRF = 0xFF;
}
static uint8_t count = 0;
void loop()
{
// Translate 'count' to Gray Code and output.
PORTF = GRAY_CODE[ count ];
// Toggle LED pin.
digitalWrite( LED_PIN, ( count & 0x01 ) );
// Delay for a bit.
delay( 250 );
// Next...
count += 1;
}