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    Axon II Microcontroller


    Technical details for those technically inclined.

    SoR Datasheets Axon Datasheets App for Android
    Offline version of Axon series datasheets - for those emergency situations when you don't have internet access.
    (download at Android Market)


      Axon II Microcontroller Dimensions

      Total weight is 34 grams.
      Four 4-40 screw holes make mounting onto your robot easy.



      Unlike the original Axon, the Axon II has two different power configurations.

      The default battery configuration requires just one battery to operate the Axon II - just like the original Axon. All Axon IIs are manufactured and shipped in this default configuration. You can also attach additional batteries in parallel on the unregulated battery bus (all batteries must be the same voltage, battery type, and charge level) as needed.

      The dual battery configuration allows you to use a small stable battery for powering sensors and the ATmega640, while a much larger less stable power supply can be used for motors and/or servos. In this configuration, the battery meant to be regulated goes on the BAT header, while the other battery goes anywhere on the unregulated battery bus. To enable this configuration, flip over your Axon II and remove the small solder trace between BAT and G5. This trace acts as a high-current jumper.

      For an example on how to change the battery configuration, please see this video:

      Absolute minimum required voltage is 5.35V. If at any time the voltage drops below this amount, even for a milli-second, the Axon II will reset. The recommended battery voltage is 6V to 7.2V (a 6V 1000mAh+ NiMH battery works great). Maximum voltage at 16V, however most servos will have reduced lifetimes at voltages above ~6V and can quickly fail at voltages ~7.2V+.

      There are three power buses. ADC pins 0 to 15 are regulated at 5V, while all other pins are directly connected to your battery. There is also two 3.3V output pins (see current tolerances).

      The Axon II has polarity protection features, meaning that it is designed to protect itself if you accidentally plug your battery in reverse. However, it will NOT protect any external component(s) connected to the unregulated battery bus.

      The 3.3V power bus is NOT protected against polarity or power surges, so be careful or you'll fry your USB.

      This is how the pins are set up in terms of power.

      Axon II Power Bus Key

    Axon II Power Bus Locations
      Pins	Voltage
      Bat	battery (input)
      G5-B7	battery
      H7-L7	battery
      A0-A2	5V regulated
      0-15	5V regulated
      3.3V	3.3V (output)
      G	ground
      -	ground


      In addition to normal digital I/O functionality, some pins come with additional special features.

      Hardware PWM
      Hardware PWM is perfect for creating a perfect high frequency squarewave without any cost to the processor. Servos using hardware PWM can only be used on 16 bit pins, while regular DC motors can be used on any PWM pin.
      8-bit timer pins: G5 (T0), H6/B4 (T2)
      16-bit timer pins: B5/B6/B7 (T1), E3/E4/E5 (T3), H3/H4/H5 (T4), L3/L4/L5 (T5)

      The UART is great for sending and receiving serial data, such as from a GPS, a camera, external memory, other microcontrollers, etc.
      pins: U0, U2, U3, U1 is connected to USB

      The ADC, or analog to digital converter, is great for reading in analog sensor data (Sharp IR, photoresistor, accelerometers, gyros, etc).
      pins: 0-15 (F0-F7, K0-K7)

      External Interrupts
      External interrupts are useful for triggering interrupt code when important external events occur. Use these for encoders, sonar, and other time important sensors.
      pins: E4-E7 and D0-D3 (I2C, UART 1 pins)


      All ADC power bus pins get power from the 5V LDO voltage regulator with maximum allowable current of 1.5A. If the regulator overheats, such as from overuse or shorting, it will protect your Axon by triggering a temporary thermal shutdown. Adding a heat sink to the regulator will allow for higher power consumption. See the FAQ for more on heat sinks.

      The Axon II has been tested to handle at least 6A on each power bus, but can in theory safely handle up to ~13A. Placing your high current draw components near the battery can up this number. This limitation is entirely based on power bus tracing thickness, meaning that if you require higher currents you must make your own separate power bus. Using multiple batteries distributed along the power bus can reduce current across individual traces.

      Individual I/O pins can supply about ~20mA power, each. Exceeding this number could damage/fry the I/O pin.

      The Axon II also has a special regulated 3.3V output bus, great for components or sensors that require this low voltage. This pin cannot supply more than about 73mA, or 90mA if you aren't using USB. If you find that USB becomes unstable or fails to work when using this output, make sure you aren't overdrawing current and place a 4.7mF tantalum capacitor (polarized) between 3.3V and ground. Don't use any device with 3.3V that is likely to transmit a power surge during use.

      If you exceed the specs of the 3.3V output, you can permanently damage the USB. Do not just plug anything into it without first verifying the current draw is ok and that no voltage transients will occur.

      You must also keep in mind the current tolerances of the included Hitec 572125S on/off switch. Quoting Hitec:
      "A conservative estimate would be in the 10 amp range for the 572125S and 16 amp range for the 54407S. But again these are just estimates."
      - Hitec Sales Manager


      The Axon II has an in-built LED display. It can display any number you want, and the small dot works as a status LED. If you want to just activate a particular LED on the display, use this as a guide.

      LED Display


      All electronics creates electronic noise and sudden voltage spikes/drops that can potentially cause problems. The Axon II has been intentionally designed to minimize this noise, and in fact during extensive tests I found no detectable (non-negligible) noise for robotics purposes. However, your needs may be different. If you find you are using highly sensitive sensors, I recommended attaching additional noise suppression ceramic capacitors in parallel with the regulated power bus.


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