PCB Plotter (prototype) 
 
 
 
Specifications
Description 3-axis PCB plotter
Processor Intel 8749 Micro
2 Motors 4-Phase Steppers
Power 12V/5V Dual-Voltage Power Supply
4 Limit sensors 2 X-axis, 2 Y-axis
Digital Signals 1 Output, 1 Input
Date Created August 1993
 
The PCB plotter was created to ease circuit board fabrication for prototype circuits.  The  plotter permits movement in 3 axes: 2 horizontal and 1 vertical.   Movement in the horizontal plane is accomplished with 2, 4-phase stepper motors which permit circuit drawings as large as 6" x 7".   The vertical axis of movement is accomplished with a solenoid actuator which engages the pen.  The plotter frame was constructed from 3/4" wood, sectioned into 2 compartments.  The smaller compartment contains the electronics, including power supply and controller board.  The larger compartment houses the mechanisms which drive the table, including belt, motor, and pulley assemblies.
 
PCB Plotter
(click to enlarge)
 

The plotter has 2 moving platforms platforms, each of which has a set of 4 large nylon rollers which ride on metal tracks.  The large, horizontal platform functions as a table on which a circuit board is placed.  The smaller, vertically mounted platform provides support and mounting for the pen actuator.
 
 
Underside view		  
Underside view, power supply
 

The plotter is controlled by a custom-designed intelligent STPC-10 stepper controller.  This controller provides simulatneous control of 2 stepper motors.  It also provides +/- inputs for limit sensor switches which automatically shut off a motor when the limit is actuated.  Also provided is 1 digital input and 1 digital output.  The application of these signals is user-specifiable.  For the purpose of the plotter, the digital output is used to control the solenoid pen actuator.  The digital input confirms the position of the pen, up or down.
 

 
 STPC-10 Controller & Cabling
 
The central component of the STPC-10 is an Intel 8049 microcontroller.  The board contains port connectors for 2 stepper motors, 4 limit sensors, power supply, and host controller.  STPC-10  firmware was developed using custom assembler designed for Intel MCS-48 instructions.  The controller communicates with the host PC via parallel port and accomodates a number of predefined commands including: Set Absolute, Set Relative, Load, Set Direction,  Find Home, Set Velocity, Full-Step, Half-Step, Set User Output, and Get User Input.

 

 Underside view
 

The host software was also custom-developed, written in C.  This software contains a simple GUI for designing a circuit using pads and traces.  Once the circuit has been designed, the user prepares a bare copper-clad board, loads a marker pen, and starts the plotter.   Once the plot has completed, the board is ready to be etched and drilled.
 

Pen Actuator
 
 
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