3.8 Jumper Quick Reference
The Cerebellum package comes with six jumpers; three of these jumpers are used to configure the external power bus options, and three are used to configure serial and i2c communication, as well as update the Cerebellum firmware and force downloading.
3.8.1 Power Bus jumpers
Main input power
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The Cerebellum main input power can be powered by any input source between 5.5V and 25V, that sources at least 50 milliamps. The main input power is fused with a five amp fast-acting fuse, and switched by the power switch. The main input powers a 5V linear regulator, providing logic power to the integrated circuitry, and is also available for use at the i2c port, the analog inputs, and if the user desires, the digital I/O. The 5V regulator can source up to 1 Amp of current for general use.
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Servo Power Bus
The servo power bus can be powered by either on-board 5V power, main input power, or an external power source.
- Using the Cerebellum 5V supply is suggested if you are using the servo bus signal pins as digital I/O, and are not using any servos or other high current devices.
- Using the Cerebellum main power is suggested for using servos if your input power source is in the six to seven volt range for optimal servo operation.
- Using an external power source affords you direct control over the voltage of the servo bus.
 | Always fuse the servo external power supply if you are using it. External power is not protected by the Cerebellum's onboard fuse, nor is it switched off by the main power switch. If you short an unfused external power source and ground together on the Cerebellum, it may permanently damage the Cerebellum and any circuitry attached to it! |
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Motor Power Bus
The motor power bus can be powered by either main input power or an external power source. For applications that require voltages above 12V, it is usually desirable to separate the Cerebellum's main power source from the motor power source.
| Always fuse external motor power supplies if you are using them. The Cerebellum's protective fuse does not protect the motor driver circuit when it is powered by external power. We recommend that you use a four amp fast acting fuse on your external supply. |
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This table provides a quick overview of the maximum voltage and current ratings of each bus. Use this information to choose power sources and appropriate fuses.
| Power Source | Maximum Current | Voltage Range
| | Main Input Power | 5 Amps (fused) | 5.5V-25V
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| Regulated Five volt Power | 1 Amp | 5V
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| Servo External Power | 5 Amps | User-Defined
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| Motor External Power | 4 Amps | 7V-45V
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3.8.2 Serial, i2c, and Firmware jumpers
This jumper routes the serial signals to either use the TTL serial header or the DB9 serial port. TTL serial is useful for communicating with certain external sensors, such as the CMUCam, while RS-232 is primarily used to communicate with a computer, although some external sensors may also use RS-232. More information about the serial ports is available in the serial communications section.
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This jumper enables the I2C pull-up resistors. The pull-ups adjust the line impedance of the i2c communications bus to match specified parameters. For communication with most i2c devices, the pull-ups should be enabled. However, it is occasionally necessary to disable I2C pull-ups in those cases when more than one device has pull-ups. For example, if two or more Cerebellums are communicating over i2c, only one of the Cerebellums should have I2C pull-ups enabled. For this configuration, we suggest placing the i2c jumper on the left most pin of the I2C jumper, leaving one side of the jumper disconnected. More information about the i2c communication bus is available in the i2c communications section.
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In order to download new firmware to the 16F628 firmware PIC, connect a jumper as shown. This will allow the main PIC to update the Cerebellum firmware, see the firmware update section for more information. We suggest storing the jumper on the left most pin of the PGM jumper, leaving one side of the jumper disconnected.
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| Make sure to unplug this jumper once updating is complete. Leaving the jumper in place will cause the Cerebellum to malfunction.
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If your program accidentally blocks the serial port from communicating, you may need to use the emergency program jumper to enter programming mode and download a fixed program. In order to do this, jumper the rightmost pin of the PGM jumper with the rightmost pin of the I2C jumper, as shown. For more information about emergency downloading see the emergency download section.
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| Make sure to unplug this jumper once downloading mode is entered. Leaving the jumper in place will prevent the Cerebellum from downloading the new program properly.
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