Safety Charge Pump (SCHP),
MPG Pendant, Spindle Tachometer & Relay Box
Last updated on Thursday, July 08, 2021 04:41:17 PM Mountain US Time Zone
Safety Charge Pump,
Spindle Tachometer, Infrared Reflectivity,
Tachometer Buffer Chip, PropScope,
QRB-1114 Based Portable EO IR Reflective Pickup, Relay Box
Archived Web Page
Mounted breakout board 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 (breakout board 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
breakout boardenable 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.
This Manual Pulse Generator (MPG2) has 4 pulses/detent
with 100 detents/dial revolution. Handy Pulser specs.
Pendant stored in its supplied bracket.
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.