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GATOR Microcontroller Board |
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FEATURES
DEVELOPMENT TOOLSThe GATOR GUI software comes with ready-to-run applications, but you can also use the software to upload your own programs to the board. Open source tools such as WinAVR can be used for software development, but any development tool that can create a HEX file will work. For Linux users, See our Linux page for instructions on downloading open source AVR development tools. No programmer hardware or software is required since all GATOR boards come with a USB bootloader pre-installed and ready to accept applications. The GATOR software accepts applications in the standard HEX file format. This open interface approach means you are not locked in to using our firmware or our software (but we’re betting that you’ll want to!) TECHNICAL DETAILSPOWER SUPPLYThe GATOR board is entirely powered from your computer’s USB port. All you need is your computer, a USB cable (included), and the GATOR board and you are ready to go. You can also run the GATOR board in a stand-alone configuration by providing an external 8V-15VDC power supply, such as a laboratory power supply or a 9V battery. This allows the GATOR board to be used as an embedded controller for a robot or other embedded system. Connect the external power supply to the pins shown below:
The GATOR’s power supply inputs are incredibly rugged. Internal current limiting protects your computer’s USB port. For the external power input, the GATOR is overvoltage protected and will shut down if voltages greater than 15V are applied. Up to +30V of continuous overvoltage is tolerated, and reverse voltages are also tolerated, up to -30V continuously! POWER OUTPUTThe GATOR board provides a +5V nominal output voltage for powering external circuitry. This allows you to use your computer’s USB port as a protected, current-limited power supply! See our applications page for examples of experiments that require no external power supply. Light LED’s, power digital logic chips, etc. right from your GATOR board. This +5V nominal output voltage is available regardless of whether your GATOR board is powered from a USB port or an external power supply. The voltage output pins are protected against continuous short circuits and applied positive and negative voltages up to ±30V! So go ahead and power up -- you won’t break it. Connect your external circuitry as follows:
Since this power output is highly protected, its voltage is not regulated. This means the output voltage will be near +5V only at light current loads. As you draw more and more current from this power output, the voltage will decrease (for the EE’s out there, the output voltage is fairly well modeled as a +4.7V voltage source and a 10Ω output resistance). A typical graph of output voltage as a function of load current is shown below.
Digital logic families such as HC and AHC are well-suited to this type of power supply since they will operate down to 2V (e.g., a 74HC00). TTL-logic devices (such as LS and HCT technologies) will not work as well since they expect power supply voltages to be at least 4.5V. You can also use 3.3V logic families if you take the GATOR board power output and follow it with a 3.3V positive voltage regulator. Note from the graph above that you can theoretically source current up to about 250mA, after which the internal current limiter forces the output to 0V, but you should not design for load currents greater than about 100mA. I/O PINSAll of the ATmega324P I/O pins are available for user applications except for PD0 and PD1 (used for USB communication), PC6 (controls the on-board LED) and PC7 (used for USB hardware handshaking). The remaining I/O pins (PA0-PA7, PB0-PB7, PC0-PC5, PD2-PD7) are brought out to quick-connect screw-less terminals that accept standard hookup wire. These terminals are much faster and easier to work with than conventional screw terminals or post headers and enable quick setups and teardowns. Each I/O pin is protected by a 5.1V zener diode and 510Ω series resistor. The electrical model for each pin is as follows:
This protection mechanism allows for a continuous +12V overvoltage or -9V reverse voltage on each I/O pin simultaneously, and even larger short-duration voltages. This means that you can expect your board to last a long time, even if you make mistakes from time to time. The GATOR is perfect for students or hobbyists who have a limited budget and don’t want to buy a new board every time they make a mistake. Because of the 510Ω series resistor you have to be aware of the current limitations of each I/O pin. A graph of the typical voltage-current characteristic for each pin is shown below. Only a few milliamps of current can be sourced or sunk by each pin, and this protects the microcontroller.
Digital logic device families such as HC and AHC require only microamps of input current thus will have no trouble being driven by the GATOR board’s I/O pins. However, high-current inputs, such as optoisolated inputs, may require a current boost using an external transistor or digital buffer such as a 74HC244. ANALOG-TO-DIGITAL CONVERSION PINSThe A/D converter peripheral of the ATmega324P is shared with I/O pins PA0 through PA7. These I/O pins have the same resistor-diode protection as the other I/O pins. Due to the leakage current of the zener diodes, however, applied voltages above +4.0V will be slightly distorted. It is recommended that for A/D applications that need to be highly precise that an external A/D converter be used or the sampled voltages be kept to +4.0V or less. Negative voltage inputs are not supported and will be clamped by the zener diodes. A typical input-output voltage graph of each A/D input pin is shown below. Note that the graph is very linear up to about +4.0V, at which point the zener diode starts conducting causing a voltage drop across the 510Ω series resistor.
HEADER PINSTwo rows of 0.1” header pads are provided for easy mounting to other boards using two 15-pin 0.1” header strips (not provided). These headers provide access to all I/O pins as well as the on-board +5V power supply. The pinout and row spacing are shown below:
Note that the +5V supply available on the header pads is NOT the same protected output available at the quick-connect terminal strip at the top of the board. This +5V supply is the one directly connected to the microcontroller and is not protected against short circuits or applied positive and negative voltages. Be careful in how you connect this +5V supply to external circuitry. Do not attempt to draw more than about 100mA from this supply. MECHANICAL DRAWINGA mechanical drawing of the board (without enclosure), its mounting holes, and header pin locations is shown below. All dimensions are in inches.
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