µMD0 is intended for use in hobbyist, experimental, research, and other
applications where a bug in the hardware, firmware, or software, will not
have a significant impact on the future of the Universe or anything else.
While every effort has been made to avoid this possibility, µMD2 is an
on-going development effort. We will not be responsible for any consequences
of such bugs including but not limited to damage to the construction crane you
picked up on eBay for $1.98 + shipping, financial loss from ending up in
the Antarctic when the compass orientation provided by
your home-built ring laser gyro was off
by 1,536 degrees, or bruising to your pet's ego from any number
of causes directly or indirectly related to µMD0. ;-)
Thanks to Jan Beck for providing support for enhancements
and bug fixes and tolerating my silly C coding questions.
He was also instrumental in developing the initial
µMD1 firmware and GUI. And for getting me interested
in actually getting involved in that project. If anyone had told me
six months ago that I'd be writing code in C, MIPS assembly language,
and Visual Basic - and enjoying it (sort of) - I would have suggested
they were certifiably nuts. ;-) Jan maintains the master GUI source code
as well as slightly different versions of both the µMD1 and
µMD2 firmware and a development blog on these and other projects.
Introduction
The µMD0 kit of parts includes everything necessary for
a 1 axis readout. The extension to 2 or 3 axes is left as an
exercise for the user. But unlike µMD1 and µMD2,
this is quite straightforward without adding too many gray hairs. ;-)
However, total change rate for all 3 axes will not increase above
what is was for a single axis and may actually decline.
This document provides detailed instructions for assembling the SG-µMD0
PCB Version 1.0..
A similar document will be provided when other versions are available
(which is doubful). No major changes are anticipated but since some
parts may change, it is critical to use the correct manual. Check
the marking on the PCB to confirm the version.
All components are through-hole and except as noted,
should seat flush on the
PCB. They shouldn't be suspended in mid-air swinging in the breeze. :)
Unfortunately, due to a minor error, parts are not labeled on the
silkscreen for V1.00, so the schematic and SG-µMD2 PCB layout diagram
will need to be used to identify parts placement.
A low power soldering iron with narrow tip and thin (e.g., #22 AWG) rosin-core
solder will be required. DO NOT even think about attempting this without
suitable soldering equipment. It's well worth the investment. A Weller
soldering gun or propane torch will not work. :) Rosin core solder is also
essential. And while
I'm quite confident that you never make mistakes, a means of component removal
such as a de-soldering pump (e.g., SoldaPullt™) will be highly desirable.
Screwing up component removal can easily ruin the PCB and is not covered
under the unlimited limited warranty. :-) The total investment should
not exceed $100.
Proper soldering technique will be such that the exposed solder on each
pad should be shiny with a concave profile. It should not be a blob and
just needs to fill the hole. Solder is not glue.
Some excess solder doesn't hurt anything
but looks unprofessional. A 10X magnifier may come in handy for
inspection. Residual rosin can be cleaned off with
isopropyl alcohol or an environmentally-friendly electronic solvent.
However, leaving the rosin alone is also acceptable (if ugly).
Total assembly time for a single axis system should be under one half hour
for someone proficient
in fine soldering. Cutting component leads to 1/4 to 3/8 inch before
installation will simplify soldering as the long leads won't be poking
you in the face. :( :) Then trim flush after soldering.
The Atmega 328P Nano 3.0 microcomputer is fully assembled including
all pins. So as noted in the main SG-µMD0 manual, it
can be constructed on a solderless breadboard
for testing at least. Later, it can be transferred to a prototyping
board the SG-µMD0 PCB with soldered connections. The same parts
layout can be used for either. The
only parts not included in the kit are jumper wires for the solderless
breadboard, and wiring for any cables to the photodiodes.
IMPORTANT: All the resistors are labeled using the standard color
as shown below. Normal color vision
is required to be able to identify these reliably. Even then, it is sometimes
difficult to confirm the values that differ in one band or in poor lighting.
And a magnifier may be required to read
some markings on these and other components. If in doubt, have someone
else assemble the kit or assist you.
For those not familiar with the common resistor color code
(Black/0, Blown/1, Red/2, Orange/3, Yellow/4, Green/5, Blue/6, Violet/7,
Gray/8, White/9), two of the resistors near the 8 pin UA9637 ICs in
the layout diagram are are 680 (blue-gray-brown
or 68 with 1 zero) ohms and 330 (33 with 1 zero) ohms. The gold stripe
indicates 5 percent tolerance on the value but for the use here, tolerance
doesn't matter. (It's possible the resistors you use will have 4 stripes
where 3 of them are the value and the 4th is the multiplier, along with one
for tolerance. If in doubt confirm the value with a multimeter.) The chart below is from Digikey. (If the link decays, a Web search will readily
locate another one.)
Resistor Color Code Chart (from the Digikey Web site)
Refer to the SG-µMD2 board layout below. Clicking on these
will bring up higher resolution versions in a single separate tab or window
depending on your browser settings:
.
SG-µMD0 V1.0 PCB Layout Diagrams for V1.0 Schematics (Left)
and PCB Populated for Sin/Cos Input (Right)
Print out this document so each step can be checked off ( ) as it is completed.
The parts list below assumes populating both the Sin/Cos analog parts and the
RS422 input parts. But is not required.
( ) Confirm that all parts are present and undamaged:
( ) 1x blank SG-µMD0 V1.0 PCB. Confirm the version on the
silkscreen below the location of the USB connector. Inspect for plating
or other defects.
( ) 1x Atmega 328P Nano 3.0 PCB with pins in antistatic bag or box.
( ) 1x 30 pin wide DIP socket (may be larger needing trimming) or a
pair of 15 pin SIPP socket strips.
( ) 2x 8 pin DIP socket.
( ) 2x 3 mm red LED.
( ) 2x 3 mm green LED.
( ) 3x 0.1 µF ceramic capacitor (marked with 104 or 0.1).
( ) 1x LM393P, 8 pin DIP in antistatic foam.
( ) 1x UA9637 or UA9639, 8 pin DIP in antistatic foam.
( ) 4x 100K ohm 1/8 W Resistor (Brown-black-Yellow-gold).
( ) 1x 470K ohm 1/8 W Resistor (Yellow-violet-yellow-gold).
( ) 2x 2-3K ohm 1/8 W Resistor (See color code chart).
( ) 2x 20-50K ohm 1/8 W Resistor (See color code chart).
( ) 2x 10K ohm trim-pot.
( ) 2x 100 ohm 1/4 or 1/2 W resistor (Brown-black-brown-gold).
( ) 1x 1K ohm 1/8 W Resistor (Brown-black-red-gold).
( ) 2x Osram sfh206k or similar silicon photodiode
( ) 2x 8 pin 0.3" DIP socket
( ) 4 pole screw terminal block
( ) 6 pole screw terminal block
IMPORTANT: LEDs are really fragile with respect to soldering and tend to
die open easily. Make sure the leads are not stressed when heat is
applied - the LED should be able to jiggle slightly in the holes - and
keep the iron on them for as little time as possible.
( ) If there is a large DIP socket, it is for
is for MPB1, the Teensy 4.0, and may need to be trimmed to 28 positions.
Rather than the DIP socket, there may a deep socket strip requiring
cutting and trimming, or a pair of 14 pin deep socket strips that my just
require smoothing at the ends.. If cutting is required, DO NOT attempt
to slice it between pin positions - sacrifice one position and then file
the ends smooth.
( ) Carefully insert it in the PCB confirming no bent pins. Rather
than flipping a coin :), orient it so the large cutout faces the USB to
the left. Then solder
two corners and confirm it seats flat, then solder the other pins. Inspect
for solder bridges and unsoldered pins.
( ) Install the 8 pin sockets for U1,U2 (SKT2,SKT3).
Note orientation - the cutout goes to the right as viewed in the layout
diagram. Solder and inspect for solder bridges and unsoldered pins.
( ) Install C1,C2 (0.1 µF). C1,C2 are the oval outlines
to the right of U1,U2 respectively.
( ) Install R3,R9 (100K ohms).
( ) Install R4,R10 (470K ohms).
( ) Install R5 (2-3K ohms).
( ) Install R6,R12 (1K ohms).
( ) Install R11 (20-50K ohms).
( ) Install R1,R7 (100K ohm trim-pot).
( ) Install R2,R8 (10K ohm trim-pot).
( ) Install R15 (10K ohm trim-pot).
( ) Install R2,R8 (10K ohm trim-pot).
( ) Install LED1,LED3 (3 mm red LED).
( ) Install LED2,LED4 (3 mm green LED).
The anode is the longer lead
and goes to the right as viewed in the layout diagram. The flat is the
cathode and goes to the left. Cut the leads about 1/10" from the body
if the LED can't be inserted to sit flush on the PCB. Take care not
to overheat or stress the leads on the LED when soldering. Be as quick
as possible.
( ) Install STB1,STB2 (screw terminal blocks). Make sure the entrance
holes for the wires face away from the
PCB! Solder a middle pin and confirm they are flat on the PCB, then
solder the others. Check for solder bridges and unsoldered pins.
Headers may substituted for the screw terminal blocks if desired.
( ) Test the Nano before doing anything to it. If it fails this test,
contact me before proceeding.
Connect it to a USB port using the USB A to USB Mini B cable.
Assuming the µMD0 firmware has been installed, after a
second or so, digital pin D13, the on-board LED, acts as a
heartbeat monitor and
should start flashing in some pattern not yet fully determined, but
it will be unlike the "Blink" sketch. ;-)
IMPORTANT: Don't assume the Nano has the correct firmware! Since Nanos
are used for several different kits and/or there may have been firmware
updates since it was loaded. If in doubt, load the correct firmware
before proceeding beyond this point. The
version can be confirmed in the µMD GUI, below.
It should also be spitting out data via the USB COM port. In the
Arduino IDE, go to Tools->Port and select the port that it is plugged
into. It should show something like: COM5 "Serial".
Go to Tools-Serial Monitor. A window should appear showing data
being sent to the COM port. It will be mostly boring but the 6th value
should be incrementing by 1, probably at around 1 kHz:
(The 6th value is a sequence number which should be incrementing by 1. The
other values are, well, you don't want to know what they are.)
Unplug the USB cable.
The following steps diverge depending on whether the analog (Sin/Cos) or
digital (RS422 A/B) interface is being used. Without some rework to the PCB
and enhancements to the firmware, they cannot be active at the same time,
though most of the parts will happily coexist.
Analog Sin/Cos Version:
( ) Install R0 (1K ohm typical). This is simply protection for the
USB 5V and photodiodes.
( ) Plug the LM393 IC into the U1 position.
The dot or cutout
should face to the right - these ICs are upside-down compared to the
Nano part labeling as shown in the layout diagram.
( ) Carefully plug the Nano into the 30 pin socket. The USB connector
faces off the right side of the PCB as shown in the layout diagram.
Make sure all pins are seated and none are hanging off the socket.
CAUTION: Make sure all the pins line up with their entry points in the
socket to avoid squashing the leaf spring contacts.
( ) Reattach the USB cable. After a second or so, the Nano
LED should start flashing as before. Unplug the USB cable.
( ) (Optional) Any sort of activity on the analog inputs should be able
to fool the GUI into at least twitching, though it may not count properly.
Set all the trim-pots mid-range. If LED1 and LED3 are installed, just
touching the inputs on the 4 pole screw terminal block with a moistened
finger may be sufficient to cause them to change state. If not,
carefully momentarily connecting the inputs through a 10K ohm or larger
resistor to +5 VDC should do it.
( ) Start the µMD GUI and select the COM port.
The graph should start scrolling. But now, if you do the
moistened finger thing, it should be possible to get the displacement
to at least jump up or down, though getting them to actually increment
or decrement continuously will require
a finger dance to simulate a Quad sequence. Once confirmed, unplug the
USB cable.
Congratulations, you're all set to go. ;-)
Assembly of the Photodiode Input Circuit and/or Photodiode PCB:
These simplify the mounting and wiring of the photodiodes and beam-splitters.
There are two types. They both include spots for two photodiodes, a
protection resistor, and bypass capacitor, along with a 4 pole screw
terminal block or 4 pin header. They can be mounted on a optical post or
via small screws, or using duct tape and bailing wire - or putty. ;-)
For both of these, the beam enters from the top (in the diagrams).
The larger one designated "QD1" is designed to accept a
variable attenuator plate oriented at around 30 degrees used as a
non-polarizing beam-splitter. The small angle minimizes the difference
in polarization sensitivity for the two beams. It can also accept
a NPBS or PBS cube.
The smaller one designated "QD2" or "QD3" (same thing) is
intended for a 4-6 mm NPBS or PBS cube, or small (true 50:50) beam-splitter
plate oriented at 45 degrees.
The mounting of the beam-splitter is left as a creative exercise
for the user. One option would be suitable spacers and double-sided tape
or 5 Minute Epoxy.
The photodiodes should be installed at the optimal height taking the same
care in soldering as with the LEDs - no stress on the leads and heating
for a short a time as poosible to achieve a good joint. Note that if\
using the Attenuator Plate, the actual glass piece is alightly tilted
so that the reflected beam ends up lower than the transmitted beam and
thus the two photodiodes must be installed at different heights.
1 or 2 wires or male-male jumpers can be secured at each position of
the 4 pole screw terminal blocks. Molex-type headers can be substituted
for the terminal blocks to be able to use easily detachable cables.
The are readily available but may not be included.
Digital RS422 A/B Version:
( ) Since the default firmware ONLY works using the input pins assigned
to the analog interface, jumpers must be added on the SG-µMD0 PCB to
connect the outputs of the UA9637 to these, which can be done on HDR1: Pins
4 to 2 and pins 5 to 3.
CAUTION: With these jumpers in place, the LM393 for the analog interface
should NOT be installed. Otherwise the outputs of
the UA9637 could be pulled to ground, which it may not like.
( ) (Optional) If intending to power an encoder or similar device from
the +5 VDC available from the PCB, install a jumper wire for JP1. But
pay attention to the maximum available current from your USB. This can't
be used to power a 1/2 HP motor. ;-)
( ) Plug the UA9637 IC into the U2 position. The dot or cutout
should face to the right - the IC is upside-down compared to the
Nano part labeling as shown in the layout diagram.
( ) Reattach the USB cable. One or both LEDs near U1 and U2 (if
installed may come on, and the Nano LED should start flashing as before.
( ) (Optional test) Here is the nifty bit. ;-) Moisten a finger (doesn't
matter which one) and touch the pins on STB2. With some practice, it will be
possible
to make the LEDs near U2 to go on and off as the input to the line receivers
cause them to toggle. While the behavior is not really predictable, just
the fact that they change indicates the the line receiver is working.
Since the UA9637 has some hysteresis, it latches but the slight charge
from your electric personality is enough to toggle it. CAUTION: Don't
get carried away, these parts can be damaged by static discharges.
So, no cat's fur and plastic rods, please. :( ;-)
(This will not be possible if the terminating resistors are installed, thus
the reason for holding off on them for now.)
( ) Start the µMD GUI and select the COM port.
The graph should start scrolling. But now, if you do the
moistened finger thing, it should be possible to get the displacement
to at least jump up or down, though incrementing
or decrementing continuously will require
a finger dance to simulate a Quad sequence. Once confirmed, unplug the
USB cable.
( ) (Optional) Install R13,R15 (100 ohms). These are the terminating
resistors for the RS422 inputs. 100 ohms is the default
for applications using RS422 drivers with long cables. If being driven in
some other way and/or if the cables are short, some other value may
be better or they may not be needed at all. If in doubt, use sockets.
Congratulations, you're all set to go.
Note: Even though the RS422 inputs are differential, there may need to be a
common ground between the systems. This will need to be evaluated on a
case-by-case basis.
Where the input signals are differential with approximately equal average
levels and an amplitude more than about 0.5 V, the UA9637 RS422 receivers
are all that's needed. This includes Quad-Sin-Cos analog which will
automagically convert to digital, but only if there is sufficient
drive current. Direct photodiode signals probably will not work
without buffering.
Where the input signals are single-ended such as normal TTL,
a reference voltage would need to be provided in place of the
other differential inputs Something along the lines of:
The threshold voltage should be selected to be approximately mid-way between
the nominal high and low levels. For standard TTL, this would be 1.4 V. The
resistor values can be in the 10K range with Cb of 0.5 µF. While
the SG-µMD0 PCB doesn't have locations for these parts, they could
easily be added attached to the 6-pole screw terminal block since it has
GND and can have +5 VDC on a pin.
These are for both the analog and RS422 versions. Note that the part numbers
on the PCB and schematic PDF do NOT match the ones on the pseudo-schematics in
the µMD0 manual, sorry.
The LEDs (along with their
associated current limiting resistors) can be omitted if desired.
But every digital system requires some lights! ;-)
Refer to the schematic for more details.
Common Parts
Reference Description Comments
-------------------------------------------------------------------------------
MPB1 Atmega 328P Nano 3.0 Nano soldered to header
PCB1 SG-µMD0 V1.0 PCB Custom PCB
SKT1 30 pin 0.6" DIP socket For Nano (PCB version only)
Quad-Sin-Cos Analog Version Parts List
Reference Description Comments
-------------------------------------------------------------------------------
PCB2 Quad Decoder V1.0 PCB For mounting PDs and beam-splitter
C1 Capacitor 0.1 µF U1 5 V bypass
LED1 3 mm red LED Threshold Sin, A
LED2 3 mm green LED Threshold Cos, B
R1 Trip-pot, 100K, 1/4W Sin (Channel A) Sensitivity
R2 Trim-pot, 10K Sin (Channel A) Threshold
R3 Resistor, 100K, 1/4W Sin (Channel A) trim-pot isolation
R4 Resistor, 470K, 1/4W Sin (Channel A) hysteresis
R5 Resistor, 2-3K, 1/4W Red LED current limitin
R6 Resistor, 1K, 1/8W Channel A pullup
R7 Trip-pot, 100K, 1/4W Cos (Channel B) Sensitivity
R8 Trim-pot, 10K Cos (Channel B) Threshold
R9 Resistor, 100K, 1/4W Cos (Channel B) trim-pot isolation
R10 Resistor, 470K, 1/4W Cos (Channel B ) hysteresis
R11 Resistor, 30-50K, 1/4W Green LED current limiting
R12 Resistor, 1K, 1/8W Channel B pullup
PCB2 Quad Decoder PCB PDs and bias network (optional)
PD1 Silicon photodiode Sin (Channel A) of Quad-A-B detector
PD2 Silicon photodiode Cos (Channel B) of Quad-A-B detector
SKT1 30 pin 0.6" DIP socket For Nano
SKT2 8 pin 0.3" DIP socket For LM393
STB1 4 pole screw terminal block Photodiode bias and inputs
U1 IC, LM393, 8 pin DIP Sin/Cos thresholding
RS422 Version Parts List
Reference Description
-------------------------------------------------------------------------------
C1 Capacitor,0.1 µF U2 5 V bypass
LED3 3 mm red LED RS422 A
LED4 3 mm green LED RS422 B
R13 Resistor, 100 ohms, 1/4 W Termination
R14 Resistor, 2-3K ohm, 1/4 W Red LED current limiting
R15 Resistor, 100 ohms, 1/4 W Termination
R16 Resistor, 20-50K ohm, 1/4 W Green LED current limiting
U2 IC, UA9637, 8 pin DIP RS422 line receiver
SKT3 8 pin 0.3" DIP socket For UA9637
STB2 6 pole screw terminal block Photodiode bias and inputs
.
