Electronics

Electronics for Low Level Control

 

MegaShieldDB:

  • Schematic Image
  • Board Layout Image
  • Board photo: front
    Shown without shield but with the wireless receiver board. We commonly leave out the wireless receiver, since iit has not been effective.
  • Board photo: back
    Shown with pins that accept an Arduino Mega or Uno.
  • Eagle Schematic MegaShieldDB
  • Eagle Board Layout
    Connector X1 DB25 goes to Front Panel.
    Connector X2 DB25 goes to MegaShieldTrio.
    Connector X3 DB15 goes to Joystick / E-Stop.Connector X4 DB9 goes to Steering Servo Controller.
    Connector X5 DB9 goes to Brake Servo Controller.
  • Wiring_C2PCB
  • Status (3/6/14): Operational. Vehicle #1 has connections on X2, X3, X4, and X5. Vehicle #2 has no connection on X3, X4 or X5. In a future board revision, the DB9 connectors on X4 and X5 may be replaced by standard servo interfaces.

 

Power Cable

Motor power is 36V (Red Anderson connector); Servo power is 12V (Orange Anderson connector). There are separate on/off switches for the two power supplies. In this variant, the servo battery is in parallel with the bottom 12V of motor power. In other variants, the supplies are kept separate.

Status (3/6/14): Operational on vehicle #1. The current sensors on the brake and steering servos are not presently connected.

 

Joy Stick and E-Stop

  • Joystick Schematic Image
    Connector X1 DB15 goes to MegaShieldDB.
    Connector X2 goes to the joystick.
    Connector X3 goes to a standard E-bike throttle (useful for testing) or to high level computer.
    Connector X4 is available, and not presently used. Signal names give suggested uses.
    The E-bike controller is powered by 36V, and produces a 5V signal, which powers this circuit. This circuit loses power when the motor is turned off. Turning off power sends the ~EStop signal to microcontroller C2, and tells it that there is no motor power. The Wireless EStop signal on X1-6 will open the relay and kill 36V power, shutting off the motor. This signal does not depend on the C2 processor and will be effective if C2 is halted or unresponsive.
  • Joystick interface Eagle Schematic
  • Joystick Interface Eagle Board Layout
    Status (3/6/14): Present joystick and board is operational on vehicle #1 but hand wired. There is no E-Stop. PCB has not been fabricated.

 

Front Panel

  • Photo
    The front panel has an on/off switch for 12V power. When 5V power is taken from the servos, this switch also controls 5V power to the MegaShields. At present, MegaShield power comes from a separate 9.6V battery connected to Arduino Megas C2 and C6, which produce a regulated 5V supply. Thus computer power is unswitched, and needs to be turned off by disconnecting the smaller battery.
    The front panel has switches to enable manual control or automatic (cruise) control. These are handled separately for Motor, Brakes and Steering. Thus it would be possible for the high level computer to control steering, while the speed is handled manually.
    There is a push button to start the vehicle operating under automatic control, and another button to stop. This stop button is handled by the C2 computer, which will command the brakes on and the motor off. It is separate from the EStop, which turns off power to the motor, but will not brake unless the C2 computer is responsive. The operator EStop consists in turning the key switch to disable the motor. Emergency braking can be done by squeezing the brake lever.There are 10 LEDs for status display. These can mimic the LEDs on the Arduinos which are hidden from view.
    The LED bar at the top of the panel shows battery charge.
  • Schematic Image
  • Panel Eagle Schematic
  • Panel Eagle Board Layout
    Status (3/6/14): No Front Panel. The vehicle is hard-coded to be either under joystick control or high level computer control. A Front Panel was hand-wired, but has been disassembled. The PCB version of the Front Panel has not been fabricated.

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