Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The general idea is to cut a USB extension cable (Type A plug on one end, Type A receptacle on the other) in half, splice the two data wires, splice the ground / common wire, but connect the +5 V wires to a dual banana plug that goes into a current meter. The Big Box o’ USB Junk produced a cutoff cable end with a Type A plug and a PC jumper that was supposed to connect an internal USB header to the back panel; the red blob of silicone tape conceals the jumper’s socket strip and a five-pin male header with all the wires soldered to it.
You could use a Type B plug that would go directly into an Arduino UNO (or similar), but I figured this way everybody can bring whatever cable they need for their particular Arduino, not all of which have bulky Type B receptacles these days.
The External Power version:
External Power Current Tap
The coaxial power plug goes into the Arduino and whatever you used for power goes into the socket. The Big Box o’ Coaxial Power Stuff actually had a more-or-less properly sized coaxial jack with two wires on it and silicone tape wrapped around it; I regarded that as a Good Omen and pressed it into service as-is.
These will also replace the horribly rickety collection of alligator clip leads I usually use for such measurements…
Although I don’t need another threaded plug, the most recent OpenSCAD version can handle a model including the thread dedendum:
Broom Handle Screw – full thread – solid model
This hyper-close view (as always, clicky for more dots) shows the problem: the region where the addendum and dedendum meet at the pitch cylinder consists of a bazillion tiny faces:
Broom Handle Screw – full thread – detail
The previous version simply couldn’t handle that many elements, but the new version has a parameter that I tweaked (to 100,000), allowing it to complete the rendering. Compiling to a solid model requires about 45 minutes, most of which probably involves those unprintably small facets.
The thread elements now taper slightly in the downhill direction, so that each quasi-cylinder nests cleanly inside the next to avoid the tiny slivers that stuck out of the joints in the previous model.
And the new Slic3r version (from GitHub) has better internal support for those indentations around the base, which means that AC vent plug might be build-able, too.
The OpenSCAD source code, with a few tweaks to nest the thread cylinders and properly locate the dedendum:
// Broom Handle Screw End Plug
// Ed Nisley KE4ZNU June 2013
//- Extrusion parameters must match reality!
// Print with 2 shells and 3 solid layers
HoleWindage = 0.2;
Protrusion = 0.1; // make holes end cleanly
//----------------------
// Dimensions
PostOD = 22.3; // post inside metal handle
PostLength = 25.0;
FlangeOD = 24.0; // stop flange
FlangeLength = 3.0;
PitchDia = 15.5; // thread center diameter
ScrewLength = 20.0;
ThreadFormOD = 2.5; // diameter of thread form
ThreadPitch = 5.0;
BoltOD = 7.0; // clears 1/4-20 bolt
BoltSquare = 6.5; // across flats
BoltHeadThick = 3.0;
RecessDia = 6.0; // recesss to secure post in handle
OALength = PostLength + FlangeLength + ScrewLength;
$fn=8*4; // default cylinder sides
echo("Pitch dia: ",PitchDia);
echo("Root dia: ",PitchDia - ThreadFormOD);
echo("Crest dia: ",PitchDia + ThreadFormOD);
Pi = 3.14159265358979;
//----------------------
// Useful routines
// Wrap cylindrical thread segments around larger plug cylinder
module CylinderThread(Pitch,Length,PitchDia,ThreadOD,PerTurn=32) {
CylFudge = 1.02; // force overlap
RotIncr = 1/PerTurn;
PitchRad = PitchDia/2;
Turns = Length/Pitch;
NumCyls = Turns*PerTurn;
ZStep = Pitch / PerTurn;
HelixAngle = atan(Pitch/(Pi*PitchDia));
CylLength = CylFudge * (Pi*(PitchDia + ThreadOD) / PerTurn) / cos(HelixAngle);
for (i = [0:NumCyls-1]) {
assign(Angle = 360*i/PerTurn)
translate([PitchRad*cos(Angle),PitchRad*sin(Angle),i*ZStep])
rotate([90+HelixAngle,0,Angle])
cylinder(r1=ThreadOD/2,
r2=ThreadOD/(2*CylFudge),
h=CylLength,
center=true,$fn=12);
}
}
module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
FixDia = Dia / cos(180/Sides);
cylinder(r=(FixDia + HoleWindage)/2,
h=Height,
$fn=Sides);
}
module ShowPegGrid(Space = 10.0,Size = 1.0) {
Range = floor(50 / Space);
for (x=[-Range:Range])
for (y=[-Range:Range])
translate([x*Space,y*Space,Size/2])
%cube(Size,center=true);
}
//-------------------
// Build it...
ShowPegGrid();
difference() {
union() {
cylinder(r=PostOD/2,h=PostLength);
cylinder(r=PitchDia/2,h=OALength);
translate([0,0,PostLength])
cylinder(r=FlangeOD/2,h=FlangeLength);
color("Orange")
translate([0,0,(PostLength + FlangeLength)])
CylinderThread(ThreadPitch,(ScrewLength - ThreadFormOD/2),PitchDia,ThreadFormOD);
}
translate([0,0,-Protrusion])
PolyCyl(BoltOD,(OALength + 2*Protrusion),6);
translate([0,0,(OALength - BoltHeadThick)])
PolyCyl(BoltSquare,(BoltHeadThick + Protrusion),4);
translate([0,0,(PostLength + FlangeLength + ThreadFormOD/2)])
rotate(-90)
CylinderThread(ThreadPitch,ScrewLength,PitchDia,ThreadFormOD);
for (i = [0:90:270]) {
rotate(i)
translate([PostOD/2,0,PostLength/2])
sphere(r=RecessDia/2,$fn=8);
}
}
Rather than start with the stepper, I wired an LED and resistor between output bit 07 and Field Ground at the power supply:
Mesa 5i26-7i76 with LED
It’s worth noting that the terminals labeled GND on TB2 and TB3 are isolated from the Field GROUND terminal on TB1. When Mesa says “isolated power supply”, that’s exactly what they mean.
The digital output bits connect +24 VDC Field Power to the load, which should then connect to Field GROUND. I picked a good-looking 5 V panel LED from the pile, simply because it had wires soldered to it from a previous life, and put a 1 K resistor in series to drop the other 19 V.
Then you start up HAL, load the Mesa drivers, and twiddle the bit:
The thread runs with a 1 ms period, mostly because it’s convenient. The .read and .write pins transfer data from and to the 5i25 FPGA each time the thread runs; if you forget those, nothing happens.
Setting the output bit true activates the output bit, turns on the MOSFET driver, and connects the terminal to Field Power = 24 VDC. The 7i76 outputs do not sink current, they source it.
A journey of a thousand 3D printed objects starts with a single LED…
The watchdog timer ought to be connected to something more fragile and UI-related than the main thread, but I haven’t figured out how to do that yet.
First up: note that Mesa uses a capital I (“eye”) in the part numbers, a decision which they’ve surely had plenty of time to regret, as many common fonts exhibit nearly identical capital-I and digit-1 characters.
The 7i76 connects to the 5i25 in the PC through a Mesa-supplied IEEE-1284 printer cable. I cobbled up a 24 VDC power supply (which I’ll eventually be using for the M2 motors) to provide “field power” and let the firmware identify the daughtercard:
24 VDC power supply – Mesa 7i76 – stepper driver
The default jumper positions on both cards work fine.
The unconnected stepper driver brick and motor will serve as a simple demonstration after I’ve built the Eagle parts to represent the 5i25’s components. However, the first demo of any new hardware must be a blinking LED.
To see whether the cards work and are detected, load the hostmot2 drivers in halrun and dump all the information:
halrun
halcmd: loadrt hostmot2
halcmd: loadrt hm2_pci
halcmd: show all
Loaded HAL Components:
ID Type Name PID State
5 RT hm2_pci ready
3 User halcmd5010 5010 ready
4 RT hostmot2 ready
Component Pins:
Owner Type Dir Value Name
5 bit OUT FALSE hm2_5i25.0.7i76.0.0.input-00
5 bit OUT FALSE hm2_5i25.0.7i76.0.0.input-00-not
5 bit OUT FALSE hm2_5i25.0.7i76.0.0.input-01
... snippage ...
5 bit OUT FALSE hm2_5i25.0.7i76.0.0.input-30
5 bit OUT FALSE hm2_5i25.0.7i76.0.0.input-30-not
5 bit OUT FALSE hm2_5i25.0.7i76.0.0.input-31
5 bit OUT FALSE hm2_5i25.0.7i76.0.0.input-31-not
5 bit IN FALSE hm2_5i25.0.7i76.0.0.output-00
5 bit IN FALSE hm2_5i25.0.7i76.0.0.output-01
... snippage ...
5 bit IN FALSE hm2_5i25.0.7i76.0.0.output-15
5 bit IN FALSE hm2_5i25.0.7i76.0.0.spindir
5 bit IN FALSE hm2_5i25.0.7i76.0.0.spinena
5 float IN 0 hm2_5i25.0.7i76.0.0.spinout
5 s32 OUT 0 hm2_5i25.0.encoder.00.count
5 s32 OUT 0 hm2_5i25.0.encoder.00.count-latched
5 bit I/O FALSE hm2_5i25.0.encoder.00.index-enable
5 bit IN FALSE hm2_5i25.0.encoder.00.latch-enable
5 bit IN FALSE hm2_5i25.0.encoder.00.latch-polarity
5 float OUT 0 hm2_5i25.0.encoder.00.position
5 float OUT 0 hm2_5i25.0.encoder.00.position-latched
5 s32 OUT 0 hm2_5i25.0.encoder.00.rawcounts
5 s32 OUT 0 hm2_5i25.0.encoder.00.rawlatch
5 bit IN FALSE hm2_5i25.0.encoder.00.reset
5 float OUT 0 hm2_5i25.0.encoder.00.velocity
5 s32 OUT 0 hm2_5i25.0.encoder.01.count
... snippage ...
5 float OUT 0 hm2_5i25.0.encoder.01.velocity
5 bit OUT FALSE hm2_5i25.0.gpio.000.in
5 bit OUT TRUE hm2_5i25.0.gpio.000.in_not
5 bit OUT FALSE hm2_5i25.0.gpio.001.in
... snippage ...
5 bit OUT TRUE hm2_5i25.0.gpio.032.in
5 bit OUT FALSE hm2_5i25.0.gpio.032.in_not
5 bit OUT TRUE hm2_5i25.0.gpio.033.in
5 bit OUT FALSE hm2_5i25.0.gpio.033.in_not
5 bit IN FALSE hm2_5i25.0.led.CR01
5 bit IN FALSE hm2_5i25.0.led.CR02
5 u32 IN 0x00000000 hm2_5i25.0.sserial.channel
5 u32 IN 0x00000000 hm2_5i25.0.sserial.parameter
5 u32 IN 0x00000000 hm2_5i25.0.sserial.port
5 u32 OUT 0x00000000 hm2_5i25.0.sserial.port-0.fault-count
5 u32 OUT 0x00000000 hm2_5i25.0.sserial.port-0.port_state
5 bit IN TRUE hm2_5i25.0.sserial.port-0.run
5 bit IN FALSE hm2_5i25.0.sserial.read
5 u32 OUT 0x00000000 hm2_5i25.0.sserial.state
5 u32 IN 0x00000000 hm2_5i25.0.sserial.value
5 bit IN FALSE hm2_5i25.0.sserial.write
5 bit IN FALSE hm2_5i25.0.stepgen.00.control-type
5 s32 OUT 0 hm2_5i25.0.stepgen.00.counts
5 float OUT 0 hm2_5i25.0.stepgen.00.dbg_err_at_match
5 float OUT 0 hm2_5i25.0.stepgen.00.dbg_ff_vel
5 float OUT 0 hm2_5i25.0.stepgen.00.dbg_pos_minus_prev_
5 float OUT 0 hm2_5i25.0.stepgen.00.dbg_s_to_match
5 s32 OUT 0 hm2_5i25.0.stepgen.00.dbg_step_rate
5 float OUT 0 hm2_5i25.0.stepgen.00.dbg_vel_error
5 bit IN FALSE hm2_5i25.0.stepgen.00.enable
5 float IN 0 hm2_5i25.0.stepgen.00.position-cmd
5 float OUT 0 hm2_5i25.0.stepgen.00.position-fb
5 float IN 0 hm2_5i25.0.stepgen.00.velocity-cmd
5 float OUT 0 hm2_5i25.0.stepgen.00.velocity-fb
5 bit IN FALSE hm2_5i25.0.stepgen.01.control-type
... snippage ...
5 float OUT 0 hm2_5i25.0.stepgen.09.velocity-fb
5 bit I/O FALSE hm2_5i25.0.watchdog.has_bit
... snippage ...
Parameters:
Owner Type Dir Value Name
5 bit RW FALSE hm2_5i25.0.7i76.0.0.output-00-invert
5 bit RW FALSE hm2_5i25.0.7i76.0.0.output-01-invert
... snippage ...
5 bit RW FALSE hm2_5i25.0.7i76.0.0.output-15-invert
5 u32 RO 0x100000A5 hm2_5i25.0.7i76.0.0.serial-number
5 bit RW FALSE hm2_5i25.0.7i76.0.0.spindir-invert
5 bit RW FALSE hm2_5i25.0.7i76.0.0.spinena-invert
5 float RW 100 hm2_5i25.0.7i76.0.0.spinout-maxlim
5 float RW 0 hm2_5i25.0.7i76.0.0.spinout-minlim
5 float RW 100 hm2_5i25.0.7i76.0.0.spinout-scalemax
5 u32 RO 0x00000000 hm2_5i25.0.7i76.0.0.status
5 bit RW FALSE hm2_5i25.0.encoder.00.counter-mode
5 bit RW TRUE hm2_5i25.0.encoder.00.filter
5 bit RW FALSE hm2_5i25.0.encoder.00.index-invert
5 bit RW FALSE hm2_5i25.0.encoder.00.index-mask
5 bit RW FALSE hm2_5i25.0.encoder.00.index-mask-invert
5 float RW 1 hm2_5i25.0.encoder.00.scale
5 float RW 0.5 hm2_5i25.0.encoder.00.vel-timeout
5 bit RW FALSE hm2_5i25.0.encoder.01.counter-mode
... snippage ...
5 float RW 0.5 hm2_5i25.0.encoder.01.vel-timeout
5 bit RW FALSE hm2_5i25.0.gpio.000.invert_output
5 bit RW FALSE hm2_5i25.0.gpio.000.is_opendrain
5 bit RW FALSE hm2_5i25.0.gpio.001.invert_output
... snippage ...
5 bit RW FALSE hm2_5i25.0.gpio.030.invert_output
5 bit RW FALSE hm2_5i25.0.gpio.030.is_opendrain
5 bit RW FALSE hm2_5i25.0.gpio.030.is_output
5 bit RW FALSE hm2_5i25.0.io_error
5 s32 RO 0 hm2_5i25.0.pet_watchdog.time
5 s32 RW 0 hm2_5i25.0.pet_watchdog.tmax
5 s32 RO 0 hm2_5i25.0.read.time
5 s32 RW 0 hm2_5i25.0.read.tmax
5 s32 RO 0 hm2_5i25.0.read_gpio.time
5 s32 RW 0 hm2_5i25.0.read_gpio.tmax
5 u32 RW 0x00000001 hm2_5i25.0.sserial.port-0.fault-dec
5 u32 RW 0x0000000A hm2_5i25.0.sserial.port-0.fault-inc
5 u32 RW 0x000000C8 hm2_5i25.0.sserial.port-0.fault-lim
5 u32 RW 0x00077FE2 hm2_5i25.0.stepgen.00.dirhold
5 u32 RW 0x00077FE2 hm2_5i25.0.stepgen.00.dirsetup
5 float RW 1 hm2_5i25.0.stepgen.00.maxaccel
5 float RW 0 hm2_5i25.0.stepgen.00.maxvel
5 float RW 1 hm2_5i25.0.stepgen.00.position-scale
5 u32 RW 0x00000000 hm2_5i25.0.stepgen.00.step_type
5 u32 RW 0x00077FE2 hm2_5i25.0.stepgen.00.steplen
5 u32 RW 0x00077FE2 hm2_5i25.0.stepgen.00.stepspace
5 u32 RW 0x00077FE2 hm2_5i25.0.stepgen.01.dirhold
... snippage ...
5 u32 RW 0x00077FE2 hm2_5i25.0.stepgen.09.stepspace
5 u32 RW 0x004C4B40 hm2_5i25.0.watchdog.timeout_ns
5 s32 RO 0 hm2_5i25.0.write.time
5 s32 RW 0 hm2_5i25.0.write.tmax
5 s32 RO 0 hm2_5i25.0.write_gpio.time
5 s32 RW 0 hm2_5i25.0.write_gpio.tmax
Parameter Aliases:
Alias Original Name
Exported Functions:
Owner CodeAddr Arg FP Users Name
00005 fc3d2582 f1b17000 NO 0 hm2_5i25.0.pet_watchdog
00005 fc3c49dc f1b17000 YES 0 hm2_5i25.0.read
00005 fc3c4906 f1b17000 YES 0 hm2_5i25.0.read_gpio
00005 fc3c4936 f1b17000 YES 0 hm2_5i25.0.write
00005 fc3c48d6 f1b17000 YES 0 hm2_5i25.0.write_gpio
... snippage ...
Extract the 5i25 pin assignments from the kernel log file: dmesg | grep hm2
I am, perhaps, easily confused, but it took me a while to realize those pin assignments apply to the 5i25 back panel and on-card connectors, not the 7i76 daughter card’s screw terminals. Yeah, it says 5i25 right there in the dump, but …
The Fine 7i76 Manual gives the 7i76 pin connections, so they’re not even slightly hidden. [sigh]
Unlike most Arduino courses, I assume you’re already OK with the programming, but are getting tired of replacing dead Arduinos and want to know how to keep them alive. The course description says it all:
Learn how to help your Arduino survive its encounter with your project, then live long and prosper. Discover why feeding it the proper voltages, currents, and loads ensures maximum Arduino Love!
Ed will describe some fundamental electronic concepts, guide you at the workbench while you make vital measurements, then show you how to calculate power dissipation, load current, and more. You’ll understand why Arduinos get hot, what kills output bits, and how you can finally stop buying replacements.
Among other lab exercises, we’ll measure the value of the ATmega’s internal pullup resistors, which everybody assumes are 20 kΩ, but probably aren’t. Hint: you can apply Ohm’s Law twice to that simple circuit and come up with the right answer, but only if you’ve measured the actual VCC voltage on the board.
The Mighty Thor will detail how to not prepare Fried Raspberry Pi.
In the unlikely event you’re in Highland NY, stop by: you’re bound to learn something.
I planned to use an old Dell Inspiron 531S AMD desktop for the LinuxCNC installation, but it turned out to have terrible interrupt latency, despite fiddling with all the available BIOS settings and video drivers. Mostly, it ran fine, but would occasionally burp up a millisecond-long latency spike for no apparent reason. So it’s now on the harvest / recycle heap.
A new-to-me off-lease Dell Optiplex 760 Core 2 Duo in the SDT (Small Desktop Tower) configuration has similar latency numbers:
Optiplex 760 latency – isolcpu 1
What’s important here is that the latency remains rock-solid stable at those numbers. Contrary to my experience with the D520 and D525 Atoms, isolating one CPU for the real-time tasks didn’t make any noticeable difference, but it’s running that way because the overall performance isn’t a problem.
Latency around 20 μs is near the upper limit for successful software step generation at any reasonable pace; the LinuxCNC description has more details. In round numbers, running the M2 at 500 mm/s needs a 40 kHz step rate in 1/16 microstep mode = a 25 μs period, which means 20 μs of jitter wouldn’t work well at all. Which is why I’m using Mesa FPGA card to get hardware step generation: it makes such problems Go Away.
The Optiplex arrived with Windows Vista Business preinstalled; it dates back to mid-2009. I used System Rescue CD to shrink the Windows partition, added a few more, then installed LinuxCNC direct from the CD image (based on Ubuntu 10.04 LTS) and Xubuntu 13.04. The latter serves as a general-purpose installation for times when I don’t need LinuxCNC, because 10.04 is pretty much obsolete for anything other than real-time control.
Digression 1: Yes, 10.04 LTS. TheRTAI project hasn’t released the patches that will slip the real-time kernel under the stock 3.x Linux kernel: LinuxCNC remains stuck at 10.04 LTS. Those changes have been coming Real Soon Now for quite a while; as with most Open Source projects, they could use more manpower and money. This isn’t a problem, as LinuxCNC is used for motion control, not a general-purpose operating system.
The SDT case has room for two PCI cards and one PCI-E video card, so I installed the dual-head video card that couldn’t handle the U2711 monitor’s dual-DVI connection (although I’m using only DVI Output 1) and a Mesa 5i25. The middle “card” is actually a tiny PCB connected to a ribbon cable that brings out a second serial port (remember serial ports?) and what could be either or both of a PS2 keyboard or mouse connection (remember PS/2?).
Optiplex 760 SDT – dual DVI – serial – 5i25
The back panel has a parallel printer port (which may come in handy for something) and a serial port, although you’re expected to have USB mice and keyboards these days. The front panel even has a floppy drive…
Digression 2: LinuxCNC does not require a parallel printer port; this seems to be a common misconception among folks who don’t actually know how it works. The Mesa 5i25 FPGA card with a 7i76 step-direction daughter board provides high-resolution timing for five axes, rotary encoder inputs, a bunch of buffered digital I/O bits, a watchdog timer, plus various other useful odds and ends, all behind handy screw terminals.
The Optiplex 760 has on-board VGA-class video that would also work fine, but the monitor I’m using has its VGA input connected to the box driving the Sherline mill and an unused DVI input. Having that dual-DVI monitor card lying around, I figured I could attach the same monitor to both systems and just poke the monitor’s input section button; I’ve found KVM switches unreliable in this application.
The usual setup preps the system for public-key SSH on a nonstandard port, sets up the NFS mounts, and tweaks this-and-that: it’s running just fine.
Digression 3: SSH kvetches when you swap server boxes at the same IP address, as well it should. If you’re foolish enough to have two separate Linux installs on the same box with the same IP, SSH reminds you every time you boot the other distro…
The Smell of Molten Projects in the Morning 