Breakout Board, Safety Charge Pump (SCHP), MPG Pendant, Spindle Tachometer & Relay Box
Last updated on Monday, January 28, 2019 09:59:11 AM Mountain US Time Zone


Breakout Board, Safety Charge Pump, MPG Pendant, Spindle Tachometer, Infrared Reflectivity,
Tachometer Buffer Chip, PropScope, QRB-1114 Based Portable EO IR Reflective Pickup,
Relay Box

Breakout Board

Mounted 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.  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 output (BOB pin 14). 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.

Breakout board chassis underneath the bench.

The SCHP master enable switch is mounted on the breakout board enclosure underneath the bench.
The cable to the right is attached to the bench switch.

The far left red momentary-on switch now replicates that enable function at a much more accessible location.

LPT2 pendant C22 v2.4 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 (0378 hex) & LPT2 is a PCI card (DF00 hex). The Port #1 address
 is standard but the Port #2 port address can vary so examine the computer's devices menu.

Low-profile LPT2 PCI card.

MOBO LPT1 is the main I/O for the stepper motors & signals like spindle, mist, E-stop, & digitizing probe.
LPT2, shown here, is dedicated to only the MPG pendant control.  Lava Parallel-PCI/LP Installation Manual

Mini-DIN chassis bracket.

A collar with four small set screws holds the mini-DIN connectors together more securely.

MPG Pendant

This Manual Pulse Generator (MPG2) has 4 pulses/detent with 100 detents/dial revolution. Handy Pulser specs.

Pendant stored in its supplied bracket. There are reports that the wireless MPG's are unreliable.


Click on linked thumbnails

Used extra scale brackets to allow hanging the pendant at three different bench edge locations.

Encoder/MPG tab. Pendant Manual Pulse Generator (MPG) inputs to LPT2.
The 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 that are not in use. The MPG's white button is pressed after an axis is selected.
This setup is for the
LPT2 pendant C22 v2.4 interface board powered via USB. Use the latest brain.

Axis_JogRes_SelectorLPT2.brn Enabled
EnableLPT2.brn Enabled
E-stop_W_AutoResetLPT2.brn Enabled
DisableLPT2.brn Disabled
E-stop_WO_AutoResetLPT2.brn Disabled

MPG Calibrate window. The MPG can also be setup using the MPG 4-6 Plug-in & its Readme 1st file.
I found the Mach3 MPG 4-6v3 plug-in control method to be a better implementation than the Brains.

Spindle Tachometer

Fairchild QRB1114 E-O sensor, Delrin tachometer pick-up housing & back plastic cover.
This is an updated design from an earlier DRO projectE 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.

# 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.


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.










Click on linked thumbnails

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.

QRB-1114 Based Portable EO IR Reflective Pickup

Portable EO Infrared (IR) reflective probe. The signal output is measured using a PropScope oscilloscope.

The housing is 1/2" ID PVC with tight-fitting nylon end plugs. A slot was cut to hold the QRB-1114 EO device.

Same circuit as the mill tachometer pick-up.

Entire circuit slides into the front end.

Two, 1/4-20 threaded holes on the right (90 deg apart) are for tripod mounting.

A nylon plug closes the end. It has an 8-32 threaded hole so it can be pulled back out of the housing.

A white, flathead nylon screw holds the sensor in the housing. A 5 VDC wall transformer supplies the power.

IR photo of the QRB-1114 emitter shown glowing at 940 nanometers.

Probe aimed at the turning Taig lathe motor pulley covered with black tape except for an exposed area to sense.

PropScope measurement of the pulley speed. 29.8Hz x 60 = 1788 RPM.

A plastic cap effectively protects the sensor when in storage.

The probe being used to measure the 1s focal-plane shutter speed of my 1951 Leica IIIf GR camera.
A piece of aluminum (duct) tape was inserted into the film plane to provide strong IR reflectivity.

Shutter set to 1s; measured 0.979s. Within ANSI suggested +/-25% low-speed
shutter accuracy standards & quite good for a 60+ years old mechanical camera.

Relay Box

A relay box for Mach3 control of the spindle motor, mist/coolant, vacuum, etc.

Modeled after Tom Benedict's relay box design. Since I used a plastic enclosure instead of metal, I mounted
the two Crydom D2425 solid-state relays onto a 1/4" aluminum heat-sink plate. Heat-sink compound was thinly
spread over the entire back of the relays. The thick plate allowed for tapped holes to mount both the devices
 (8-32) & the plate to the enclosure using (10-32, flush-mounted, 100 deg flat-head screws). Each relay controls two
sockets. These relays are perfect for this application as they use TTL with built-in opto-isolation. The 15A fuse is
for the hot 110VAC input. The plastic enclosure is 4-3/4" x 4-3/4" x 2-3/8". Metal is a better choice for an enclosure.

The plastic cover was supported during milling by clamping the entire assembled box in the vise.
The domed galvanized metal cover gives good durability & extra room for wiring.

Note: Maximum off-state leakage current at rated voltage is 10 mA rms. It can affect certain circuits.

The Mach3 tutorial explains how to setup, enable & test the pin outs.

LEDs indicate the status of Mach3 output signals calling for spindle and/or mist/flood AC power.
The LED current-dropping resistors on the plus data lines are insulated with clear heat-shrink tubing.









Click on linked thumbnails

Uses LPT1 output pins 16 & 17 via the opto-isolated BOB & set in Mach3.
 System Schematic
The relays have opto-isolation built-in so the circuit is (unnecessarily) double-isolated.

Heat would build-up when the circuit powered the spindle at 10K RPM for 5 hours using a 1/3 HP motor.
Though it did not even begin to approach the
Crydom max ambient operating temperature of 176 deg F (80 deg C),
I added an external heat sink that extended the internal mounting plate. First, I cut away the insulating layer.

Two, 1/4" aluminum plates were milled to size. The plastic is 3/32" thick.

Corners filed out for the radius. Both sides of the heat-transfer plate were coated with heat-sink compound.

This modification more than doubled the amount of heat sink metal.

The three plates (inside, transfer, & outside) were then clamped together. Air can circulate via convection
over both sides of the radius-edged plate. The bolt heads will also act as spacers/feet if it is used on its
backside. There are nuts & washers to hold the inner plate in its original place against the plastic housing.
Now the unit only becomes lukewarm after prolonged (>5 hours), high-speed (10K RPM) spindle use.

Breakout Board, Safety Charge Pump, MPG Pendant, Spindle Tachometer, Infrared Reflectivity,
Tachometer Buffer Chip, PropScope, QRB-1114 Based Portable EO IR Reflective Pickup,
Relay Box