Another advantage of the board is that it is fully
configurable via a CAN network and no power-cycle is
necessary for any change to take effect. The three classic
models of PID controllers are programmed into the board and
are one of the many parameters that the end user can
select. Controller gains, maximum and minimum PWM commands,
and Device ID are also configurable. All configuration
values are stored in the dsPIC's EEPROM so once it is
configured at the full contempt of the end-user, no more
changes are required.
The board has inputs for two limit switches that indicate
the beginning and end of the total run. The board is able
to position the motor in a range from 0 to 1.677e7 turns
with the resolution depending on the encoder being used. If
the CMRE module is used, then a 0.35 degrees-of-turn
precision is obtained (which can be greatly increased if
the motor is geared or runs a threaded mechanism).
The
board has only one power supply which can range from 7.5 to
40 volts which is used to drive the motor. From the same
power supply a step-down DC-DC converter generates 5 volts
for the TTL logic. Overall the design fits in a 3.1 by 3.1
inches, two layers PCB and, as shown in the included
pictures, is easily mountable on the back-end of a motor.
The board is also equipped with an ICSP connector allowing
the firmware to be completely upgradeable even once it has
been deployed.
This
project won a
Distinctive Excellence award during the Circuit Cellar -
Microchip 2007 Embedded Control Design Contest. You can
read the full project report submission here.