Breakout Board
Mounted
C1 breakout board (BOB) having opto-isolation
on all lines; independent PC (USB) & stepper-side
power supplies.
This board is in between the PC & the stepper controller. The smaller card
is the LPT2
C22 pendant interface
which uses USB supplied power. The box has a metal cover.
System Schematic
LPT1 (steppers), LPT2 (pendant) & three power cables; two
are USB & the mini-DIN is an external power supply.
The separate external power supply energizes the non-computer, equipment side of the
opto-isolation board.
Opto-isolated LPT1 stepper-motor controller, spindle/mist/vacuum relay
box control, limits/homing,
E-Stop inputs, & MPG2 pendant.
The right ribbon cable seemed to have allowed electrical noise
from the steppers into the pendant circuit so it has since been made into a direct
connection.
Breakout board detail. The LEDs are helpful but an
oscilloscope is better for diagnostics.
Safety Charge Pump
Safety charge pump with the
tachometer buffer chip
mounted off the corner.
The LPT1 pin out logic states are
unknown when they are not under direct control of a program, e.g.,
Mach3.
I/O can change during a system reboot or if the OS/Mach3 become corrupted,
possibly causing unexpected
signals to be sent to the CNC motors. To eliminate this potentially dangerous
problem, Mach3 can generate a
12.5kHz square-wave signal output (pin 1). This signal is only present when
Mach3 has control of the motors.
The safety charge pump circuit monitors these pulses but if they are turned off
or disrupted, it opens a relay in
the E-Stop circuit, drops the enable signal to the opto-isolation board &
signals Mach3 to halt all LPT1 signals.
To activate the charge pump, a momentary (NO) switch is needed to enable the
breakout board. Under Mach3
General Configuration window, the Charge Pump On in EStop is selected to
allow a quick push/release of the
BOB enable button turning on the pump, otherwise, the momentary enable switch
has to be held down while
simultaneously clicking on Mach3's master reset button. The
tachometer input buffer chip is now held by the
plastic
screw mount at the corner of the safety charge pump circuit board. C4 safety pump manual &
wiring.
LPT2 pendant C22 interface board powered via USB. The
C1 breakout board's +5V
enable signal
goes
through the two, NC E-Stops & this board's
NO (blue) relay which is controlled by the pendant's E-Stop
button. The E-Stop circuit now also goes through the NO (blue) relay of the
safety charge pump circuit.
In the BIOS, turned-off the two RS232 serial ports & configured the two LPT
ports to EPP+ECP.
LPT1 is on the motherboard (Hex 0378) & LPT2 is a PCI card (Hex
d000). The Port #1 address
is standard but the Port #2 port address can vary so examine the computer's
devices menu.
Mini-DIN chassis bracket.
A collar with four small set screws holds the mini-DIN connectors together more
securely than friction, alone.
MPG Pendant
This
Manual Pulse Generator (MPG2) has 4 pulses/detent. There are 100 detents/dial
revolution.
Handy Pulser specs.
It is very important to perform the Mach3 jog control CAL. Disable any Mach3
brains (see setup guide) that are not in use.
Pendant stored in its supplied bracket.
Used extra scale brackets to allow hanging the pendant at three different bench edge locations.
Varies from the instructions.
| PENDANT BRAIN SETUP | |
| BRAIN | STATUS |
| Axis JogRes Selector.brn | Enabled |
| Enable.brn | Enabled |
| Disable.brn | Enabled |
| E-Stop W AutoReset.brn | Disabled |
| E-Stop WO AutoReset.brn | Enabled |
| ModIOMPG.brn | Disabled |
Spindle Tachometer
Fairchild QRB1114 E-O sensor, Delrin tachometer pick-up housing & back plastic cover.
This is an updated design from an
earlier
DRO project. E is the emitter & S is the sensor.
Tachometer pick-up housing (back). The cover keeps
out debris & prevents electrical shorts.
The
Fairchild QRB1114 E-O sensor was
first glued
in using water-proof silicon & then wired.
Buffer/Tachometer circuit.
Philips 74HC/HCT244 octal
buffer driver used in the tachometer circuit.
The Fairchild QRB1114
940nm
E-O sensor housing was mounted using Taig, pre-existing 10-32 tapped holes.
Aimed directly at the pulley center hub with a 0.2875"
gap. It easily detects the
dark set screw.
| MEASURED RPM | |
| # | 100% RPM |
| 1 | 555 |
| 2 | 950 |
| 3 | 1456 |
| 4 | 2174 |
| 5 | 3333 |
| 6 | 5555 |
| 7 | 8160 |
| 8 | 25000 |
Motor shaft turns 1795 RPM. Measured
spindle speeds. Mach3 pulley
assignments for
the Taig Micro Mill.
Unless Mach3 is controlling the spindle speed, leave it on defaults (25000
RPM) so no error is generated.
Instead of gluing, a black plastic screw now retains the
sensor.
Infrared Reflectivity
A near-infrared (NIR) camera picture, using the
Sony DSC-F717 night shot
mode, showing
the Fairchild NIR emitter glowing at 940 nanometers (nm) which is invisible to the
naked eye.
Note how the Delrin & sensor housing appear dark but the black plastic retaining screw is
white indicating high
reflectivity in the NIR.
Objects that appear light or dark to the eye can exhibit either high or low
NIR reflectivity.
This characteristic must be taken into account when selecting materials for use in NIR reflective
tachometer
pick-up assemblies.
For example, if the pulley's black set screw had high NIR reflectivity, it
would not have
activated the
sensor properly. This principle applies to all materials including: plastic,
metal, paint, tape, etc.
Selecting a material based solely on its visual appearance may cause a
sensing failure.
Added an index pulse card to sense a slotted disk for the Taig CNC lathe.
The tachometer pick-up cable was run along with the
limit-switch cable, inside the same protective sheathing.
Tachometer (3-conductor stereo type) input jack &
Teflon-covered cable.
Tachometer Buffer Chip
The 74HC/HCT244
(octal buffer driver) signal is inputted to LPT1, pin 15 (LED on). Tachometer/buffer
circuit
The mill tachometer index is now on pin
11 & the lathe
tachometer index is on pin 15.
The original Parallax USB
oscilloscope used to make
the
signal measurements.
Tachometer/buffer signal output
at 555 RPM (9.25 Hz x 60 seconds/minute).
Tachometer/buffer signal output
at 5555.4 RPM (92.59 Hz x 60 seconds/minute).
Tachometer input signal setup via Mach3's ports & pins, input signals,
index
enabled, LPT port 1, pin 15, active low.
The mill tachometer index is now on pin
11 & the lathe
tachometer index is on pin 15.
In General Logic Configuration, do not have high debouncing/noise
rejection values as they affect the higher RPM readings.
PropScope
The PropScope USB storage oscilloscope is supplied with
two, 1x/10x BNC probes & expansion card.
Upgraded USB PropScope by Parallax
has many more measurement capabilities than their original USB oscilloscope.
The plug-in DAC expansion card has connections for the function generator (FGN),
an external
trigger (TRG) & the Logic State Analyzer (LSA).
Channel 2 is disabled when the DAC card is plugged-in.
See the
startup document &
user manual for the PropScope. Also see
XYZs of
Oscilloscopes primer.
An example of the PropScope generating & then measuring a
1kHz square-wave signal. The probe has a trimmer that is adjusted until the
square wave is flat-topped.
An example of a PropScope hybrid screen displaying the
oscilloscope, spectrum analyzer, & XY plot of the two, exactly the same,
in-phase signals.
Another example of a PropScope hybrid screen displaying the oscilloscope &
Logic State Analyzer.
