I need to create a cable that has 4 LEDs attached every 3m. The cable will be 40m long and will have some control electronics at the beginning. The purpose of the cable will be a LED chaser.

I've read whatever I could find here and elsewhere about LED chaser and they all focus on CD4017 and 555's. My requirement is anything that is efficient.

I was thinking of some cheap MCU and 15 miniature PCB's connected with SPI, but at best that would give me about 20 wires in the cable to create a LED chaser.

Is there a better way with less wires?? I don't need the complete solution I just need someone to point me to a better solution.

Anything is acceptable, LED driver chips, I2C, SPI, CAN, whatever can get me to as few wires as possible.

  • \$\begingroup\$ you can get raw ws2811 interfaces or pre-soldered rgb modules for cheap. (4 wires w/power) \$\endgroup\$ – dandavis Jan 13 '18 at 11:48
  • \$\begingroup\$ It depends what you mean by a LED chaser. If 6 groups of LEDs that turned on in pairs like ABcdef -> aBCdef -> abCDef -> abcDEf -> abcdEF -> AbcdeF -> etc etc would be adequate, then that can be done with 3 wires without multiplexing (ie with LEDs at full brightness). The same arrangement can light each group individually to any brightness, multiplexed with a corresponding decrease in maximum brightness. \$\endgroup\$ – Neil_UK Jan 13 '18 at 13:11
  • \$\begingroup\$ Look into NeoPixels and DotStar. \$\endgroup\$ – Russell Borogove Jan 13 '18 at 14:55

You could do it with three wires (power, ground and signal) and a set of MCU's. You have one master node which send data out of the UART TX pin. The others all pick it up at their RX pin. You make a 2-byte protocol. e.g. first byte always has MS bit set which indicates an address giving you 128 slaves to talk to. Second byte has MS bit clear which is the LED pattern to output giving you control of 7 LEDs per MCU. You may need to boost the output of the master TX with a good driver IC but that depends on your baudrate.

Just though of an alternative: chain the MCU's up. The first one picks up the data and re-transmit it at it's tx if it is not for him. This makes that each MCU needs to talk only to the next one: lower driver strength. Note that both schemes give you more then a simple LED chaser as you can make any pattern you want.

  • \$\begingroup\$ +1 good solution. You can deal with the fan out problem in the master controller by using appropriate drivers. Your action section of the message is either LED on or LED off which leaves you potentially with 128 address and 1 action in one byte depending on the protocol chosen. \$\endgroup\$ – RoyC Jan 13 '18 at 15:46

Cable signals Power, Ground, Reset, Shift clock, Shift Signal. Shift signal is daisychained from MCU to MCU.

No need for SPI. First MCU generates a low frequency shift clock at chase frequency and every no of leds shift clocks creates a Shift signal. It also creates the reset at the start of each chase cycle to guarantee the state of the devices in the chain.

All the other MCUs read their shift signal in on the rising edge of the shift clock and if present raise their own shift signal out and turn on the led if no shift signal in turn off the LED and turn off the shift signal out. You can do that with one D type but MCUs are probably cheaper these days and give you some flexibility in what you can do particularly for noise rejection in this application.


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