This page contains the source code portion of the Basic Stamp 2 program that controls the turntable. Note that this program is written using the PBASIC 2.5 version. The complete version 2 code and documentation can be downloaded using this link:  TurntableV2.zip The original code is available here:  Turntable.zip

' ======================================================================
' TurntableV2.bs2                                             5-03-2005
'
' Note: This program is written using {$PBASIC 2.5} features.
'
' This program is used to control the engine terminal turntable on the
' D&B model railroad. This portion of the layout consists of two approach
' tracks and a number of engine storage tracks. A maximum of ten turntable
' track positions are supported. The rotating turntable bridge track is
' positioned using a stepper motor based upon user input via a keypad.
' Track numbers are entered using a 12 button telephone style keypad and
' cause the turntable bridge to rotate and align to the specified track
' number. All turntable track positions are user input via the keypad. This 
' provides completely arbitrary approach and storage track positions.
'
' User input turntable bridge track positions are stored in the Basic Stamp 
' NVRAM. In this way, the bridge track position programming is not lost when 
' power is removed. The following memory map describes this storage area. 
' All storage locations are a word (two bytes) in size.
'
'    Address     Description
'    -------     ----------------------------------------------------
'       0        Circle size - calculated by programming mode 0 key.
'       2        Head end position for key 0 - operate mode 0# keys.
'       4        Head end position for key 1 - operate mode 1# keys.
'      ...       Head end position for keys 2 through 8.
'      20        Head end position for key 9 - operate mode 9# keys.
'      22        Tail end position for key 0 - operate mode 0* keys.
'      24        Tail end position for key 1 - operate mode 1* keys.
'      ...       Tail end position for keys 2 through 8.
'      42        Tail end position for key 9 - operate mode 9* keys.
'
' When programming a bridge track position, the final rail alignment stepping 
' should be done in a clockwise direction for proper gear backlash elimination.
' This program incorporates the program constant PosAdj. In operate mode, the 
' value of this constant is used to overstep the specified track position when 
' moving in a counter-clockwise direction. The turntable bridge is then im-
' mediately stepped the same PosAdj amount in the clockwise direction resulting
' in the final rail aligned position. Depending on the drive gear reduction
' used, this constant may need to be adjusted slightly.
'
' Mechanical considerations:
'
' The D&B model railroad uses a turntable bridge gear ratio of 12 to 1. This 
' results in a step circle of 9,600 steps using a 3.6 degree stepper motor 
' (100 steps) that is 8x micro-stepped (800 steps = 360 degrees). In use, 
' this circle size results in a single step of about one eighth an HO scale
' rail width which has proven to be more than enough accuracy. 
'
' Other combinations of gear ratios, stepper motors (e.g. 1.8 degree step), 
' and micro-step settings can be used up to a maximum of 65,535 steps in the 
' circle (16 bit word). Higher ratios may introduce more gear backlash that 
' must be taken into account (PosAdj constant). Some planning and compromise 
' that involves the desired rotation speed, position accuracy, and gear back-
' lash is necessary. No program code changes are required for other gear 
' ratios or stepper motors other than the backlash PosAdj constant. The total
' steps in the circle is computed and stored by this program in response to 
' the Programming mode '0' key.
'
' This design does not currently include any bridge track position feedback
' other than the home position sensor. All movements are based upon the home 
' position that is located at power on time. The method used to gear the stepper
' motor and bridge track must be carefully considered to ensure accurate and 
' repeatable positioning. Any bridge track rotational binding or rough spots 
' must be eliminated. Gearing backlash should also be minimized. The prototype 
' successfully uses the stock gears provided with the Walthers Cornerstone 
' Series (R) turntable, part number 933-3171. Another method would be to use a
' miniature tooth/timing belt and pulley design.  
'
' Program mode:
'
' The keypad is used to manually position the turntable bridge and assign
' the position to a keypad number button. This information is stored in the
' BS2 NVRAM for reference during operate mode. It is necessary to enter this
' data only when the turntable related track configuration is changed;
' normally following the laying of the track.
'
' Each turntable position has a head-end and tail-end which corresponds to
' the bridge track end. No specific keypad button to track mappings are
' enforced. The same bridge track position and head/tail alignment may be
' programmed for multiple keypad buttons if desired.
'
' The following summarizes the keypad buttons and corresponding functions
' that are used in program mode.
'
'    Button     Function
'    ------     ----------------------------------------------------------
'       0       Find home position and calculate circle size
'       1       Microstep turntable bridge counter-clockwise
'       2       Head-end of turntable bridge track aligned (default)
'       3       Microstep turntable bridge clockwise
'       4       Step turntable bridge counter-clockwise
'       5       Tail-end of turntable bridge track aligned
'       6       Step turntable bridge clockwise
'       7       Slew turntable bridge counter-clockwise
'       8       Remove current position data for track number/alignment
'       9       Slew turntable bridge clockwise
'      **       Enter/exit program mode
'      #x       Associate current turntable bridge position and head/tail
'               input with specified track number.
'
' Note that turntable motion keys 1, 3, 4, 6, 7, and 9 will auto-repeat when
' held down for more than 1/2 second.
'
' The following warning tones can occur in program mode:
'
' 1 tone  - Circle size too large. Need less steps in circle.
'
' 2 tones - Unknown turntable bridge position or circle size. Do program
'           mode key '0' first.
'
' 3 tones - Invalid keypad input.
'
' Programming example:
'
' The following example illustrates the steps used to input the information for
' the approach track and two storage track positions. The approach track is
' assigned to button 1 and the storage tracks to buttons 2 and 3. Storage track
' 2 is then removed. It is assumed that the controller circuit is connected to
' the turntable motor, power is applied, and the BS2 heartbeat indicator is
' flashing.
'
' It is recommended that a locomotive be placed on the bridge track during
' programming. The weight of the locomotive has a slight effect on the final
' position due to gear drive backlash.
'
' For reference in this programming example, the head-end of the turntable is
' the end where the operators shack is mounted. The keypad buttons '1', '3',
' '4', '6', '7', and '9' are collectively referred to below as the 'move'
' buttons.
'
'  1. Press the '*' key twice to enter programming mode. The heartbeat Led
'     changes to solid on to show that programming mode is active. If three
'     short tones are heard, an invalid key value was detected and is likely
'     caused by a keypad wiring error.
'
'  2. Press the '0' key. This finds the turntable bridge home position. If not
'     found, the turntable bridge will rotate continuously in a counter-clockwise
'     direction indicating a wiring or sensor problem. The turntable bridge is
'     then rotated once in a clockwise direction to determine the circle size.
'
'  3. Use the 'move' buttons to rotate the turntable bridge and accurately align
'     the head-end bridge track with the approach track. The final alignment
'     should be done in a clockwise direction to eliminate gear backlash.
'
'  4. Press the following buttons in order: '2', '#', '1'.
'
'  5. Use the 'move' buttons to rotate the turntable bridge and accurately align
'     the tail-end bridge track with the approach track. The final alignment
'     should be done in a clockwise direction to eliminate gear backlash.
'
'  6. Press the following buttons in order: '5', '#', '1'.
'
'  7. Use the 'move' buttons to rotate the turntable bridge and accurately align
'     the head-end bridge track with storage track one. The final alignment
'     should be done in a clockwise direction to eliminate gear backlash.
'
'  8. Press the following buttons in order: '2', '#', '2'.
'
'  9. Use the 'move' buttons to rotate the turntable bridge and accurately align
'     the tail-end bridge track with storage track one. The final alignment
'     should be done in a clockwise direction to eliminate gear backlash.
'
' 10. Press the following buttons in order: '5', '#', '2'.
'
' 11. Use the 'move' buttons to rotate the turntable bridge and accurately align
'     the head-end turntable track with storage track two. The final alignment
'     should be done in a clockwise direction to eliminate gear backlash.
'
' 12. Press the following buttons in order: '2', '#', '3'.
'
' 13. Use the 'move' buttons to rotate the turntable bridge and accurately align
'     the tail-end bridge track with storage track two. The final alignment
'     should be done in a clockwise direction to eliminate gear backlash.
'
' 14. Press the following buttons in order: '5', '#', '3'.
'
' 15. To remove the head-end aligned entry for storage track two, press the
'     following buttons in order: '8', '2', '#', '2'.
'
' 16. To remove the tail-end aligned entry for storage track two, press the
'     following buttons in order: '8', '5', '#', '2'.
'
' 17. Press the '*' key twice to exit programming mode. The heartbeat Led
'     returns to operational flash rate; once per second.
'
' 18. Use operate mode turntable positioning commands to verify proper operation.
'     Reprogram individual tracks if necessary.
'
'     x# - Head-end of turntable should align to the specified track number.
'     x* - Tail-end of turntable should align to the specified track number.
'
' Operate mode:
'
' Two button presses are entered via the keypad to rotate the turntable bridge
' track. The first button pressed is the desired track number. The second button
' pressed is the turntable bridge end to align to the specified track. The
' turntable bridge track is rotated following the second button input. The keypad
' entry indicator will flash during the turntable bridge move operation.
'
' A solid 'on' keypad entry indicator is used to show that a track number has
' been input and the program is waiting for a turntable bridge track end button to
' be pressed. If a turntable bridge track end button is not pressed within about
' 5 seconds, the entered track number button is ignored.
'
' Upon power up, the program initiates a search for the home position sensor.
' This involves stepping the turntable bridge in a counter-clockwise direction
' until the home position sensor returns an active state. This search operation
' can be aborted by pressing any key during the search operation. The next bridge
' movement, in program or operate mode, will redo the home position search.
'
' Two automatic turntable bridge movements can be enabled by the setting of program
' constants.
'
' The first optional movement, if enabled, is performed after initial power up.
' It permits automatic turntable bridge positioning to an initial track position.
' The constants InitPos1 and InitPos2, when both non-zero, identify a track and
' turntable bridge end respectively. The values specified should be the keypad
' number of a programmed track position (InitPos1 e.g. 1, 2, etc.) and the bridge
' end (InitPos2 e.g. 10 (*) tail end or 11(#) head end).
'
' The second optional movement, if enabled, results in random turntable bridge
' positioning. If the constant RandomMove is set to a non-zero value, the value
' represents a time delay. Each toggling of the heartbeat indicator (about 1 second)
' will cause a counter set to this value to be decremented. When the counter reaches
' zero, the turntable bridge will be positioned to a random track and bridge end.
' The time delay is then restarted. A user commanded move will also reset the time
' delay.
'
' RandomMove set to a value of 255 results in about a 4-5 minute delay between auto
' moves. The actual time between moves may be a longer multiple of this time since
' bridge positioning will only be performed if the random track/end position values
' are actually programmed.
'
' The following summarizes the keypad buttons and corresponding functions that
' are used in operate mode.
'
'    Buttons    Function
'    -------    -------------------------------------------------------------
'      x#       Position turntable bridge track head-end to track number 'x'.
'               'x' is a button 1 through 9.
'      x*       Position turntable bridge track tail-end to track number 'x'.
'               'x' is a button 1 through 9.
'      00       Re-index to home position sensor. Same as power on operation.
'      11       Toggle position of lead track turnout 1.
'      22       Toggle position of lead track turnout 2.
'
' The following warning tones can occur in operate mode:
'
' 1 tone  - Unprogrammed track number specified. Program track number.
' 2 tones - Unknown turntable circle size. Redo program mode key '0'.
' 3 tones - Invalid keypad input.
'
' Turntable Lead Track Turnouts:
'
' The turnouts that provide access to the tracks associated with the turntable
' can be controlled by this program. The operational mode command 11 is used
' to change the position of turnout 1. The command 22 is used to change the
' position of turnout 2. Each entry of the 11 or 22 key sequence will toggle
' the position of the respective turnout; from closed to open or open to closed.
' The turnouts do not employ position sensors. The program assumes the turnouts
' are closed at power up.
'
' Turntable Bridge Track Power:
'
' The turntable bridge track must be powered by a polarity reversing circuit. An
' external circuit (MRC-AR auto reverser) is used to control the power polarity
' of the turntable bridge track.
'
' All storage tracks are wired to the same polarity as the lead track. These
' tracks are all connected to the "non-switched" power controller output. The
' turntable bridge track is connected to the power controller "switched" output.
'
' Hardware:
'
' The turntable control circuit uses the 74C922 keypad encoder to interface
' and debounce the push button key input. The capacitors associated with the
' 'osc' and 'msk' inputs determine the key scan rate and debounce time period;
' 600 hz and 10 msec respectively.
'
' The stepper motor is a 12 volt unit with a 3.6 degree step angle. The stepper
' motor is driven by an Allegro 3977 stepper motor controller which provide a
' simplified interface to the BS2 and the ability to microstep the motor. Micro
' stepping is used to provide the necessary accuracy for turntable bridge track
' rail alignment. The resistors used to set the stepper motor holding current
' are a compromise between overall power draw, stepper motor heat, and the 
' weight of the largest locomotive to be turned. 
'
' A 74LS38 quad open collector NAND gate is used to drive the switch machine
' coils for the approach track turnouts. Each turnout control bit is connected
' to the base circuit of a TIP127 5 amp darlington transistor. When a turnout is
' to be positioned, the program selects the appropriate NAND gate and pulses
' the common NAND gate inputs for a nominal 250 ms. This causes the TIP127 driver
' circuit to energize the turnout coil.
'
' An input pin of the Basic Stamp is connected to a position sensor that is
' used to identify the turntable bridge rotation reference point. If continuous
' 360 degree rotation of the turntable bridge occurs, a sensor circuit problem
' is the likely cause.
'
' An output pin of the Basic Stamp is connected to a Led and used to indicate
' the status of operator keypad input.
'
' An input pin of the Basic Stamp is connected to a switch and used to select
' normal or test mode program operation. When off (1), normal turntable func-
' tions as described herein are enabled. When on (0), test mode is enabled.
' In test mode, the turntable bridge will be stepped from its current position
' approximately 60 degrees clockwise. It is then stepped 60 degrees counter-
' clockwise. This sequence will be repeated as long as test mode is enabled.
' If the home sensor position is crossed during either motion, a short chirp
' tone will be sounded.
'
' Also during test mode, pressing a keypad button will result in key number
' of tones being sounded with 0 = 10, * = 11, and # = 12 tones respectively.
'
' The normal/test mode pin is also connected to a led that serves as a
' heartbeat indicator.
'
' An output pin of the Basic Stamp is connected to a speaker and used to
' sound warning or input error tones.
' ======================================================================
      

Navigation:   Turntable   D&B Home   Buczynski.com Index

Copyright © 2006 Don Buczynski
San Diego, California