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Indicator Lights and Sounds - custom LED and/or piezo electronics allowed?

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  • Indicator Lights and Sounds - custom LED and/or piezo electronics allowed?

    Our team had the idea to mount indicator lights on a motor-driven mechanism, which would be two separate LEDs - one for when the motor is on, and one for when the motor is off. The simplest way to do this is probably with transistors on a circuit board, hooked up passively to the same wires that drive the motor itself. However, it's unclear to me whether that's legal for Freight Frenzy. RE13 suggests that it might be legal, but the prohibition on "custom circuits" suggests that it would not.

    Another way to signal would be with a piezo buzzer, and again, sound effects seem to be allowed, but custom circuits are not.

    Neither of these applications would use a programmable microcontroller. There might be a 555 timer IC at most, with basic electronic parts - LEDs, piezo buzzers, resistors, capacitors, transistors for hardware logic.

    It would be a great way to introduce team members to soldering, as well as to give the robot some character -- but only if it's legal. If anyone has clarity on this, it would be very helpful.


    Patty Rutins
    Coach FTC#16221

  • #2
    Hi Patty, you can connect multiple LEDs to the sensor ports via LED controller or directly to digital out ports. Then command the LEDs on/off in your opmodes when you command the motors on/off. Is there a reason to connect the LEDs to the motor wire instead?


    • #3
      The main reason to hook to the motor wire is that it's right there and has the signals we need. If it's not legal, though, then sure, it's a good idea to hook into the sensor port. We probably won't have so many sensors that we'd run out of available ports, even if it would require a port per device. Can we use a bit of breadboard for mounting with appropriate resistors?

      Also, would a piezo buzzer be legal if hooked into one of the sensor ports, using a timer IC and appropriate resistors?

      At what point does a little bit of style cross the line into "custom circuits"?



      • #4
        If you're soldering components, that's a pretty good indicator that it's a custom circuit.


        • #5
          Rutins, the circuits you've described are unlikely to be legal.

          I recommend the MR Color Beacon. Although initially not legal when fist introduced, the MR color beacon has been legal for the past several seasons.

          You can connect over a dozen MR color beacons to a single I2C bus. The rules say you need to use a REV Logic Level Converter for each color beacon.

          We've tested 4 MR color beacons running off of a single logic level converter. This works flawlessly, as expected, but sadly not legal. So it will cost $41 plus cabling for every MR color beacon on a bot.

          Since you mentioned soldering, a cheaper alternative is a DIY color beacon using the NXP PCA9685 I2C LED Controller. The PCA9685 can control sixteen (16) LEDs which means you can create 5 color beacons using a single PCA9685 (and a single I2C address).

          Adafruit sells a PCA9685 Breakout for only $15. So you can create 5 color beacons for only $15 plus the cost of the LEDs, 3D printing and cabling. It costs $205 for 5 MR color beacons plus 5 REV logic level converters (if you can find them).

          For Input connect [VCC, SDA, SCL, GND] to a I2C bus of a REV hub. For Output connect [PWM, GND] to Red, Green, and Blue LEDs to form a beacon. Do not connect anything to V+.

          Since the PCA9685 is a LED Controller you don't need a resistor to limit the current through the LEDs. The PCA9685 will limit the current to 10mA.

          Use a Adafruit QT Py - SAMD21 and Arduino IDE or CircuitPython to develop and test your PCA9685 I2C driver and color beacon logic. Use Adafruit's PCA9685 I2C drivers as a starting point. After your I2C driver and color beacon logic is production ready, simply port your driver and logic to your OpMode.

          Fantastic fodder for the Engineering Notebook/Portfolio.

          BOM for I2C Driver Development Platform:5 color beacons plus a complete I2C driver development platform for less than the cost of a single MR Color Beacon !!!