27906 Parallax Inc, 27906 Datasheet - Page 3

• Manufacturer Part Number: 27906
• Description: BASIC STAMP ACT BOARD NO PWR
• Manufacturer: Parallax Inc

Specifications of 27906

• Module/board Type: Activity Board
• For Use With/related Products: BASIC Stamp®
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Theory of Operation
The Position Controller is designed to manage certain operations associated with wheel motion that
traditionally consumed system resources, processing power, and execution time in the main
microcontroller.
microcontroller is free to focus on more important tasks.
Each Position Controller has an on-board microcontroller which continually tracks the position and
average speed of the wheel.
switches generate a quadrature encoded waveform which is processed by the microcontroller. Based on
the rate and specific sequence of the pulses, it is possible for the Position Controller to determine how
fast, and in which direction, the wheel is turning.
The current position value appropriately increments or decrements by 1 each time there is a waveform
transition. The current average speed value is updated every 20 ms and is an accumulated average over
the previous 0.5 seconds.
instantaneous speed of the wheel. See the Command Set Details section for more information.
The Position Controller automatically generates the appropriate pulses to drive an HB-25 motor controller
(#29144; sold separately). See Interfacing with the HB-25 Motor Controller for more information. This
configuration dramatically increases the Position Controller’s functionality since it gains control over the
wheel’s position and speed rather than simply measuring them.
desired location as a set point which it continually seeks. If the wheel is rotated away from the current
set point, it increases power to the motor in the opposite direction in order to return back to the original
position. Additionally, when the wheel is being driven on an incline or decline, the Position Controller
automatically increases or decreases power to the motor to maintain the true desired speed.
The position advancement scheme is designed to move the wheel a user-set distance (TRVL command)
at a user-set maximum speed (SMAX command) with smooth user-set acceleration and deceleration
Copyright © Parallax Inc.
Sensor 1
Sensor 2
Sensor 1
Sensor 2
0 seconds
0 seconds
By using the Position Controller to manage these functions instead, the main
It is important to note that this is an average speed value, not the
1 second
1 second
In conjunction with the plastic encoder disk, two optical interrupter
Position Controller Kit (#27906)
2 seconds
2 seconds
The Position Controller stores the
Figure 1
Quadrature encoded
voltage waveforms for a
wheel rotating at 4
positions per second.
Notice that rising edges
occur first on Sensor 1,
signifying that the wheel is
rotating in the positive
direction.
Figure 2
Quadrature encoded
voltage waveforms for a
wheel rotating at 2
positions per second. In
this case, rising edges are
seen on Sensor 2 first,
signifying a negative
direction of rotation.
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