LEDs

• Blinkenlights make life better
• Original Rott-bot had just three LEDs (Rx alive, X centered, Y centered)
  • LEDs driven directly (with current-limiting resistor) from PIC pins
• Rott-bot 2000 retained those LEDs, plus:
  • "Bar graphs" to show speed (four per wheel)
  • Bi-color LEDs, green for forward, red for backward
  • Added "heartbeat" LED as well
  • And a few more in case I thought of something else
• Twenty-four LEDs in all -- not enough pins on the PIC.
• Solution: shift registers
• 74HC164 has two inputs (data and clock) and eight outputs
• Three of these chips:
  • their outputs wired to LEDs
  • their clock inputs wired to a PIC pin
  • the data input of the first '164 wired to another PIC pin
  • the data input of shift register #n hooked up to O7 of #n-1
• Twenty four bits clocked out, the LEDs show their states
• Improvement: transistor on ground path
  • Turn off LEDs while data being clocked in
  • Or if I'm worried about wasting power

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