Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
So I stuck a CD-RW drive into the Foxconn Atom box and discovered that the pushbutton on the front panel doesn’t move quite far enough to actually hit the corresponding button on the drive.
Popped another drive off the heap and tried it out, just for grins, with the same result. Evidently the cute little ribbed back on the silvered panel button (near the bottom of the picture) isn’t quite long enough.
Solution: a bit of rubberized high-traction tape stuck to the drive button (near the top of the picture).
This is a black-on-black situation, so I pushed the contrast enough that you can actually see it.
Another pass at my Logitech Dual-Action Gamepad used as an EMC2 control pendant, but this time using an Eagle ULP (User Language Program) that converts a schematic into EMC2 HAL code.
I tweaked Martin Schöneck’s original ULP a bit, added (some of the) new devices found in EMC2.4, added the corresponding Eagle symbols & devices to the library, then drew up a schematic based on my hand-hewn HAL code with some improvements. Ran the script and shazam the HAL code worked just fine (after a bit of debugging the infrastructure, of course).
The new ULP and library are not quite ready for prime time, but this is a stick in the ground to mark some progress. You can certainly use the HAL code directly, without fiddling around in the schematic: stuff the whole program (at the end of the post) in your existing (but likely empty) custom_postgui.hal file.
The schematic is, of course, much fluffier than the corresponding code, particularly because I chopped it into five easily printed pages. Here’s the Big Picture overview of what’s going on in each page; click the pix for bigger images.
The servo thread interface device in the lower left provides the halui timing. The big block in the upper left has all the Logitech gamepad buttons, including the four big ones used for Z and A axis jogging. I changed the two left-rear buttons to activate the Abort signal rather than Estop, not that I use them all that much anyway.
The two joystick knobs have pushbuttons, which I combine and use to toggle a flipflop that will select the jogging speed: fast or crawl.
I also cut the jog deadband from 0.2 to 0.1, which makes the joysticks much more responsive.
Logitech Gamepad HAL Schematic – Page 1
The big block on the left has all the gamepad’s analog axes. The HAT0X and HAT0Y axes correspond to the top-hat pushbuttons; they’re not really analog at all, although they take on -1.0 / 0.0 / + 1.0 floating point values. The window comparators determine which joystick axes are active, which comes in handy later on.
Logitech Gamepad HAL Schematic – Page 2
The HAL jogging control has a single input that sets the default speed, but the proper value is vastly different depending on whether you’re jogging with linear or angular motion. This page picks out which ini file MAX_VELOCITY value to use, converts from units/sec to units/min, then does Cool Thing #1: scales the speed so that the fast/crawl speeds work out nicely.
I use the buttons to jog rapidly from here to there, then creep up on the alignment point using the joysticks. Pressing the joysticks downward switches from Fast to Crawl speeds, which provides sort of a gearshift that’s useful for coarse / fine adjustments.
The buttons run at two speeds:
Fast: the maximum speed for the axis
Crawl: 10% of that value
The joysticks have a lower top speed:
Fast: half the maximum speed of the axis
Crawl: 10% of that value
All those values go into the mux4 block and thence to the HAL jog speed control.
Logitech Gamepad HAL Schematic – Page 3
This page does Cool Thing #2: prioritize the joystick axes and lock out the one that started moving last. The general idea is that it’s painfully easy to move the joysticks diagonally, which is great for gaming and terrible for milling machine control. A pair of flipflops for each joystick remember which axis started moving first.
If you want to move diagonally, just press the buttons; they’re not locked out, so you can do what you want.
Logitech Gamepad HAL Schematic – Page 4
The motion comes together on the last page, where scale blocks flip the direction of the Y and Z joystick axes so positive motion is upward. The multiplexers allow only the active axis of each joystick to reach the HAL analog jog inputs; you can vary the speed of that axis up to the maximum as you’d expect. The buttons drive the digital inputs that jog at that maximum speed; the Y and Z button directions get sorted out appropriately.
Logitech Gamepad HAL Schematic – Page 5
Those five pages boil down into the following code, which I manually insert into my custom_postgui.hal file, along with the tool length probe pin definition.
# HAL config file automatically generated by Eagle-CAD hal-write.ulp
# (C) Martin Schoeneck.de 2008
# Mods Ed Nisley 2010
# Path: [/mnt/bulkdata/Project Files/eagle/projects/EMC2 HAL Configuration/]
# ProjectName: [Logitech Gamepad]
# File name: [/mnt/bulkdata/Project Files/eagle/projects/EMC2 HAL Configuration/Logitech Gamepad.hal]
####################################################
# Load realtime and userspace modules
loadrt constant count=14
loadrt and2 count=9
loadrt flipflop count=4
loadrt mux2 count=5
loadrt mux4 count=1
loadrt not count=8
loadrt or2 count=9
loadrt scale count=7
loadrt toggle count=1
loadrt wcomp count=6
####################################################
# Hook functions into threads
addf toggle.0 servo-thread
addf wcomp.1 servo-thread
addf wcomp.2 servo-thread
addf wcomp.3 servo-thread
addf and2.0 servo-thread
addf and2.4 servo-thread
addf and2.3 servo-thread
addf and2.2 servo-thread
addf and2.1 servo-thread
addf constant.6 servo-thread
addf constant.5 servo-thread
addf constant.4 servo-thread
addf constant.3 servo-thread
addf constant.2 servo-thread
addf constant.1 servo-thread
addf constant.0 servo-thread
addf constant.7 servo-thread
addf constant.8 servo-thread
addf scale.1 servo-thread
addf scale.2 servo-thread
addf scale.3 servo-thread
addf mux4.0 servo-thread
addf mux2.0 servo-thread
addf scale.4 servo-thread
addf scale.0 servo-thread
addf wcomp.5 servo-thread
addf wcomp.4 servo-thread
addf wcomp.0 servo-thread
addf flipflop.1 servo-thread
addf flipflop.0 servo-thread
addf and2.5 servo-thread
addf and2.6 servo-thread
addf and2.7 servo-thread
addf and2.8 servo-thread
addf flipflop.2 servo-thread
addf flipflop.3 servo-thread
addf or2.4 servo-thread
addf or2.8 servo-thread
addf or2.7 servo-thread
addf or2.6 servo-thread
addf or2.5 servo-thread
addf or2.3 servo-thread
addf or2.2 servo-thread
addf or2.1 servo-thread
addf or2.0 servo-thread
addf not.1 servo-thread
addf not.2 servo-thread
addf not.3 servo-thread
addf not.4 servo-thread
addf not.5 servo-thread
addf not.6 servo-thread
addf not.7 servo-thread
addf not.0 servo-thread
addf constant.9 servo-thread
addf mux2.1 servo-thread
addf mux2.2 servo-thread
addf mux2.3 servo-thread
addf mux2.4 servo-thread
addf constant.10 servo-thread
addf constant.11 servo-thread
addf scale.5 servo-thread
addf scale.6 servo-thread
addf constant.12 servo-thread
addf constant.13 servo-thread
####################################################
# Set parameters
####################################################
# Set constants
setp constant.0.value +0.02
setp constant.1.value -0.02
setp constant.2.value 60
setp constant.3.value 1.00
setp constant.4.value 0.10
setp constant.5.value 0.50
setp constant.6.value 0.10
setp constant.7.value +0.5
setp constant.8.value -0.5
setp constant.9.value 0.0
setp constant.10.value [TRAJ]MAX_LINEAR_VELOCITY
setp constant.11.value [TRAJ]MAX_ANGULAR_VELOCITY
setp constant.12.value -1.0
setp constant.13.value 0.1
####################################################
# Connect Modules with nets
net a-button-minus input.0.btn-trigger or2.2.in0 halui.jog.3.minus
net a-button-plus input.0.btn-thumb2 or2.2.in1 halui.jog.3.plus
net a-buttons-active or2.2.out or2.3.in0 or2.4.in1
net a-disable not.7.out and2.5.in1
net a-enable flipflop.3.out not.7.in mux2.4.sel
net a-jog wcomp.2.in input.0.abs-z-position mux2.4.in1
net a-knob-active not.2.out or2.4.in0 and2.7.in1
net a-knob-inactive wcomp.2.out not.2.in and2.6.in1
net a-select and2.8.in0 and2.7.out
net a-set flipflop.3.set and2.8.out
net angular_motion or2.4.out mux2.0.sel
net any-buttons-active mux4.0.sel0 or2.8.out
net az-buttons-active or2.3.out or2.8.in1
net az-reset flipflop.2.reset and2.6.out flipflop.3.reset
net button-crawl scale.4.out mux4.0.in3
net button-fast scale.2.out mux4.0.in1 scale.4.in
net jog-crawl toggle.0.out mux4.0.sel1
net jog-speed halui.jog-speed mux4.0.out
net knob-crawl mux4.0.in2 scale.3.out
net knob-fast mux4.0.in0 scale.1.out scale.3.in
net n_1 constant.10.out mux2.0.in0
net n_2 and2.0.in0 input.0.btn-top2
net n_3 and2.0.in1 input.0.btn-base
net n_4 and2.0.out halui.abort
net n_5 halui.mode.manual input.0.btn-base3
net n_6 wcomp.0.max wcomp.1.max wcomp.2.max wcomp.3.max constant.0.out
net n_7 halui.program.resume input.0.btn-base4
net n_8 wcomp.0.min wcomp.1.min wcomp.2.min wcomp.3.min constant.1.out
net n_9 mux2.0.in1 constant.11.out
net n_10 constant.12.out scale.5.gain scale.6.gain
net n_11 input.0.btn-base5 or2.0.in0
net n_12 input.0.btn-base6 or2.0.in1
net n_13 constant.9.out mux2.1.in0 mux2.2.in0 mux2.3.in0 mux2.4.in0
net n_14 mux2.1.out halui.jog.0.analog
net n_15 toggle.0.in or2.0.out
net n_16 constant.2.out scale.0.gain
net n_17 constant.5.out scale.1.gain
net n_18 constant.3.out scale.2.gain
net n_19 constant.4.out scale.3.gain
net n_20 scale.4.gain constant.6.out
net n_21 halui.jog.1.analog mux2.2.out
net n_22 mux2.2.in1 scale.5.out
net n_23 scale.6.out mux2.3.in1
net n_24 constant.13.out halui.jog-deadband
net n_25 wcomp.4.max constant.7.out wcomp.5.max
net n_26 constant.8.out wcomp.4.min wcomp.5.min
net n_27 mux2.3.out halui.jog.2.analog
net n_28 halui.jog.3.analog mux2.4.out
net vel-per-minute scale.0.out scale.1.in scale.2.in
net vel-per-second mux2.0.out scale.0.in
net x-buttons-active or2.7.in0 or2.5.out
net x-disable not.4.out and2.4.in1
net x-enable not.4.in flipflop.0.out mux2.1.sel
net x-hat-jog wcomp.4.in input.0.abs-hat0x-position
net x-hat-minus wcomp.4.under or2.5.in1 halui.jog.0.minus
net x-hat-plus or2.5.in0 wcomp.4.over halui.jog.0.plus
net x-jog wcomp.0.in input.0.abs-x-position mux2.1.in1
net x-knob-active not.0.out and2.1.in0
net x-knob-inactive wcomp.0.out not.0.in and2.2.in0 and2.3.in0
net x-set and2.1.out flipflop.0.set
net xy-buttons-active or2.7.out or2.8.in0
net xy-reset flipflop.0.reset and2.2.out flipflop.1.reset
net y-buttons-active or2.6.out or2.7.in1
net y-disable not.5.out and2.1.in1
net y-enable flipflop.1.out not.5.in mux2.2.sel
net y-hat-jog input.0.abs-hat0y-position wcomp.5.in
net y-hat-minus wcomp.5.under or2.6.in1 halui.jog.1.plus
net y-hat-plus or2.6.in0 wcomp.5.over halui.jog.1.minus
net y-jog wcomp.1.in input.0.abs-y-position scale.5.in
net y-knob-active not.1.out and2.3.in1
net y-knob-inactive not.1.in wcomp.1.out and2.2.in1
net y-select and2.4.in0 and2.3.out
net y-set flipflop.1.set and2.4.out
net z-button-minus input.0.btn-thumb or2.1.in0 halui.jog.2.minus
net z-button-plus input.0.btn-top or2.1.in1 halui.jog.2.plus
net z-buttons-active or2.1.out or2.3.in1
net z-disable not.6.out and2.8.in1
net z-enable not.6.in flipflop.2.out mux2.3.sel
net z-jog wcomp.3.in input.0.abs-rz-position scale.6.in
net z-knob-active not.3.out and2.5.in0
net z-knob-inactive not.3.in wcomp.3.out and2.7.in0 and2.6.in0
net z-set and2.5.out flipflop.2.set
The ULP script that eats the schematic and poots out the HAL code:
/******************************************************************************
* HAL-Configurator
*
* Author: Martin Schoeneck 2008
* Additional gates & tweaks: Ed Nisley KE4ZNU 2010
*****************************************************************************/
#usage "<h1>HAL-Configurator</h1>Start from a Schematic where symbols from hal-config.lbr are used!";
string output_path = "./";
string dev_loadrt = "LOADRT";
string dev_loadusr = "LOADUSR";
string dev_thread = "THREAD";
string dev_parameter = "PARAMETER";
string dev_names[] = {
"CONSTANT", // must be first entry to make set_constants() work
"ABS", // 2.4
"AND2",
"BLEND", // 2.4
"CHARGE-PUMP", // 2.4
"COMP",
"CONV_S32_FLOAT", // 2.4
"DDT", // 2.4
"DEADZONE", // 2.4
"DEBOUNCE", // 2.4
"EDGE",
"ENCODER", // 2.4
"ENCODER-RATIO", // 2.4
"ESTOP-LATCH",
"FLIPFLOP",
"FREQGEN", // 2.4
"LOWPASS",
"MULT2", // 2.4
"MUX2",
"MUX4", // 2.4
"MUX8", // 2.4
"NEAR", // 2.4
"NOT",
"ONESHOT",
"OR2",
"SAMPLER", // 2.4
"SCALE", // 2.4
"SELECT8", // 2.4
"SUM2",
"TIMEDELAY", // 2.4
"TOGGLE", // 2.4
"WCOMP", // 2.4
"XOR2", // 2.4
"" // end flag
};
string init = "# HAL config file automatically generated by Eagle-CAD hal-write.ulp\n# (C) Martin Schoeneck.de 2008\n# Mods Ed Nisley 2010\n";
/*******************************************************************************
* Global Stuff
******************************************************************************/
string FileName;
string ProjectPath;
string ProjectName;
void Info(string Message) {
dlgMessageBox(";<b>Info</b><p>\n" + Message);
}
void Warn(string Message) {
dlgMessageBox("!<b>Warning</b><p>\n" + Message + "<p>see usage");
}
void Error(string Message) {
dlgMessageBox(":<hr><b>Error</b><p>\n" + Message + "<p>see usage");
exit(1);
}
string replace(string str, char a, char b) {
// in string str replace a with b
int pos = -1;
do {
// find that character
pos = strchr(str, a);
// replace if found
if(pos >= 0) {
str[pos] = b;
}
} while(pos >= 0);
return str;
}
// the part name contains an index and is written in capital letters
string get_module_name(UL_PART P) {
// check module name, syntax: INDEX:NAME
string mod_name = strlwr(P.name);
// split string at the : if exists
string a[];
int c = strsplit(a, mod_name, ':');
mod_name = a[c-1];
// if name starts with '[' we need uppercase letters
if(mod_name[0] == '[') {
mod_name = strupr(mod_name);
}
return mod_name;
}
string comment(string mess) {
string str = "\n\n####################################################\n";
if(mess != "") {
str += "# " + mess + "\n";
}
return str;
}
// if this is a device for loading a module, load it (usr/rt)
string load_module(UL_PART P) {
string str = "";
// it's a module if the device's name starts with LOADRT/LOADUSR
if((strstr(P.device.name, dev_loadrt) == 0) ||
(strstr(P.device.name, dev_loadusr) == 0)) {
// now add the string to our script
str += P.value + "\n";
}
return str;
}
// count used digital gates (and, or, etc) and load module if neccessary
string load_blocks() {
string str = "";
int index;
int dev_counters[];
string dname[];
// count the gates that are used
schematic(S) { S.parts(P) {
strsplit(dname,P.device.name,'.'); // extract first part of name
if ("" != lookup(dev_names,dname[0],0)) {
for (index = 0; (dname[0] != dev_names[index]) ; index++) {
continue;
}
dev_counters[index]++;
}
} }
// force lowercase module names...
for (index = 0; ("" != dev_names[index]) ; index++) {
if (dev_counters[index]) {
sprintf(str,"%sloadrt %s\tcount=%d\n",str,strlwr(dev_names[index]),dev_counters[index]);
}
}
return str;
}
string hook_function(UL_NET N) {
string str = "";
// is this net connected to a thread (work as functions here)?
int noclkpins = 0;
string thread_name = ""; // this net should be connected to a thread
string thread_position = "";
N.pinrefs(PR) {
// this net is connected to a clk-pin
if(PR.pin.function == PIN_FUNCTION_FLAG_CLK) {
// check the part: is it a thread-device?
if(strstr(PR.part.device.name, dev_thread) == 0) {
// we need the name of the thread
thread_name = strlwr(PR.part.name);
// and we need the position (position _ is ignored)
thread_position = strlwr(PR.pin.name);
thread_position = replace(thread_position, '_', ' ');
}
} else {
// no clk-pin, this is no function-net
noclkpins++;
break;
}
}
// found a thread?
if(noclkpins == 0 && thread_name != "") {
// all the other pins are interesting now
N.pinrefs(PR) {
// this pin does not belong to the thread
if(strstr(PR.part.device.name, dev_thread) != 0) {
// name of the pin is name of the function
//string function_name = strlwr(PR.pin.name);
string function_name = strlwr(PR.instance.gate.name);
// if functionname starts with a '.', it will be appended to the modulename
if(function_name[0] == '.') {
// if the name is only a point, it will be ignored
if(strlen(function_name) == 1) {
function_name = "";
}
function_name = get_module_name(PR.part) + function_name;
}
str += "addf " + function_name + "\t" + thread_name + "\t" + thread_position + "\n";
}
}
}
return str;
}
string set_parameter(UL_NET N) {
string str = "";
// is this net connected to a parameter-device?
int nodotpins = 0;
string parameter_value = "";
N.pinrefs(PR) {
// this net is connected to a dot-pin
if(PR.pin.function == PIN_FUNCTION_FLAG_DOT) {
// check the part: is it a parameter-device?
// str += "** dev name [" + PR.part.device.name + "] [" + dev_parameter + "]\n";
if(strstr(PR.part.device.name, dev_parameter) == 0) {
// we need the value of that parameter
parameter_value = PR.part.value;
// str += "** value [" + PR.part.value +"]\n";
}
} else {
// no clk-pin, this is no function-net
nodotpins++;
break;
}
}
// found a parameter?
if(nodotpins == 0 && parameter_value != "") {
// all the other pins are interesting now
N.pinrefs(PR) {
// str += "** dev name [" + PR.part.device.name + "] [" + dev_parameter + "]\n";
// this pin does not belong to the parameter-device
if(strstr(PR.part.device.name, dev_parameter) != 0) {
// name of the pin is name of the function
//string parameter_name = strlwr(PR.pin.name);
string parameter_name = strlwr(PR.instance.gate.name);
// if functionname starts with a '.', it will be appended to the modulename
// str += "** param (gate) name [" + parameter_name + "]\n";
if(parameter_name[0] == '.') {
// if the name is only a point, it will be ignored
if(strlen(parameter_name) == 1) {
parameter_name = "";
}
parameter_name = get_module_name(PR.part) + parameter_name;
// str += "** param (part) name [" + parameter_name + "]\n";
}
str += "setp " + parameter_name + "\t" + parameter_value + "\n";
}
}
}
return str;
}
// if this is a 'constant'-device, set its value
// NOTE: this is hardcoded to use the first entry in the dev_names[] array!
string set_constants(UL_PART P) {
string str = "";
// 'constant'-device?
if(strstr(P.device.name, dev_names[0]) == 0) {
str += "setp " + get_module_name(P) + ".value\t" + P.value + "\n";
}
return str;
}
string connect_net(UL_NET N) {
string str = "";
// find all neccessary net-members
string pins = "";
N.pinrefs(P) {
// only non-functional pins are connected
if(P.pin.function == PIN_FUNCTION_FLAG_NONE) {
string pin_name = strlwr(P.pin.name);
string part_name = strlwr(P.part.name);
pin_name = replace(pin_name, '$', '_');
part_name = replace(part_name, '$', '_');
pins += part_name + "." + pin_name + " ";
}
}
if(pins != "") {
string net_name = strlwr(N.name);
net_name = replace(net_name, '$', '_');
str += "net " + net_name + " " + pins + "\n";
}
return str;
}
/*******************************************************************************
* Main program.
******************************************************************************/
// is the schematic editor running?
if (!schematic) {
Error("No Schematic!<br>This program will only work in the schematic editor.");
}
schematic(S) {
ProjectPath = filedir(S.name);
ProjectName = filesetext(filename(S.name), "");
}
// build configuration
string cs = init + "\n\n";
FileName = ProjectPath + ProjectName + ".hal";
cs += "# Path: [" + ProjectPath + "]\n";
cs += "# ProjectName: [" + ProjectName + "]\n";
//cs += "# File name: [" + FileName + "]\n\n";
// ask for a filename: where should we write the configuration?
FileName = dlgFileSave("Save Configuration", FileName, "*.hal");
if(!FileName) {
exit(0);
}
cs += "# File name: [" + FileName + "]\n\n";
schematic(S) {
// load modules
cs += comment("Load realtime and userspace modules");
S.parts(P) {
cs += load_module(P);
}
// load blocks
cs += load_blocks();
// add functions
cs += comment("Hook functions into threads");
S.nets(N) {
cs += hook_function(N);
}
// set parameters
cs += comment("Set parameters");
S.nets(N) {
cs += set_parameter(N);
}
// set constant values
cs += comment("Set constants");
S.parts(P) {
cs += set_constants(P);
}
// build nets and connect them
cs += comment("Connect Modules with nets");
S.nets(N) {
cs += connect_net(N);
}
}
// open/overwrite the target file to save the configuration
output(FileName, "wt") {
printf(cs);
}
Most of that script is Martin’s work; I just cleaned it up. You can download it by hovering over the code to make the little toolbar pop up near the upper-right corner of the text, then:
click a little button to copy it to the clipboard or
click another little button to view the source, then save that file
You’ll also need the Eagle library that goes along with the script, but WordPress doesn’t like .lbr files. Here’s the hal-config-2.4.lbr file with a totally bogus odt extension. Download it, rename it to remove the .odt extension, and it’s all good.
There is basically no documentation for any of this. I figured out what to do by looking at the source and Martin’s sample schematic, but now you have two sample schematics: the situation is definitely improving!
Of late I’ve been toting an LED flashlight / laser pointer around in my pocket for peering into dark corners and highlighting interesting objects. It started flickering and I discovered the joint just aft of the switch had become slightly loose.
Disassembled LED Flashlight
Well, I always wondered how the thing came apart and now I know!
The threadlocking compound seems to have turned into dusty white powder, although my pocket doesn’t seem all that hostile an environment.
Flashlight innards
The switch assembly pulls out, revealing the LED circuit board with the laser module in the middle. The two wires correspond to the two ON states: flashlight and laser.
For what it’s worth, the 8 LEDs draw 130 mA (16 mA each), far more than the 3 mA each in that pathetic work light.
The laser draws 20 mA.
Screwed everything back together and it works fine again…
The Arduino Mega has an SMD voltage regulator soldered to a copper pad connected with thermal vias to a similar pad on the bottom surface. The datasheet says the (roughly) 10×10 mm copper pad sets RθJA=55 °C/W, more or less; probably a bit less with the double-sided setup.
It’s the chubby black slab snuggled up just to the right of coaxial power input jack. The four vias on each side go to an isolated copper pad under the solder mask on the other side.
Arduino Mega voltage regulator
The board draws about 75 mA with nothing fancy on the I/O pins, so the regulator dissipates half a watt with a 12 VDC input supply. Figuring an ambient of 30 °C, the junction temperature is ticking along at 50-60 °C.
That’s all well and good, but my rule of thumb for semiconductors is:
If you can’t hold your thumb on it for any length of time, it’s too damn hot.
That regulator fails my rule of thumb even before I start adding LEDs and other doodads.
A bit of rummaging turned up an old Thermalloy sample box with a DIP heatsink. A dab of quick-setting epoxy and there it is:
Arduino Mega regulator with heatsink
Now, I’ll grant you there are a number of things wrong with that approach, but my thumb is much happier. If it gets unhappy, I’ll just crack that puppy off and stick something larger in its place.
The Arduino Mega has four, count them, four mounting holes in a more-or-less rectangular pattern around the edge of the board. Three of the four have enough room for standard pan-head 4-40 screws. The fourth hole is squeezed between two pin-header sockets, to the extent that no screw in my collection will fit.
Screw on Arduino Mega board
Having a lathe, however, makes this situation no big deal… and this time, I put the Sherline drill chuck in the 3-jaw because I wanted to, notbecause the 3-jaw was stuck. In truth, the lathe chuck simply won’t grab a 4-40 screw at all.
Turning down the screw
I had that pointy right-cutting tool in the holder, so that’s how I cleared off the burr on the backside of the head.
The chuck did grab the hex standoff just fine, though, and the final result looks like this…
Modified standoff and screw for Arduino Mega
For future reference, the turned-down sections are 0.180 inch in diameter; call it 4.5 mm. The snout on the standoff must clear the pins,so it’s 0.100 inch or 2.5 mm long.
It seems I applied a bit too much pressure to one of the contacts on a metal AA cell holder: the outer rim of the rivet holding the solder tab in place departed for the distant reaches of the Basement Laboratory.
No big deal, I thought: pop another rivet in place and get back in operation…
You really want the rivet to go in with the flat head inside the cell holder where the original flat head was. Unfortunately, the rivet yanker’s head won’t fit into the holder; I’m pretty sure the manufacturer has a Special Machine to make that happen.
So I put the reinforcing washer and lumpy end inside. That meant switching the insulating washers to keep the overall distance from the negative cell contact about the same.
Cell holder rivet – inside
The outside looks much better…
Cell holder rivet – outside
For what it’s worth, these pix came from the Sony DSC-H5 with the flash turned down 1 EV. Much better results than the Casio EX-Z850, even with its flash set to Soft (whatever that is). The H5 has much better macro capability… and with the new Eneloop cells, it lasts long enough to make it usable in the shop.
So I added a cheap 72-LED worklight as a box-filler to a recent order. Popped in four AA alkaline cells, clicked the switch, and … huh, that thing looks dim.
Took it apart and what do we find inside? Resistors!
Over on the left lives a pair of 10-Ω resistors that limit the overall LED current. They’re in parallel, so it’s running with a 5-Ω ballast.
LED ballast resistors
Over on the right, each string of 24 parallel LEDs has a separate 10-Ω equalizing resistor.
LED equalizing resistors
A quick ammeter check gives the dismal news: total current is 220 mA = 73 mA per string of 24 LEDs = 3 mA per LED.
Well, no wonder why it’s dim!
The ballast resistors drop 0.22 x 5 = 1.1 V, each equalizing resistor is good for 0.073 x 10 = 0.73 V, and (as you’d expect) the LEDs run at about 4 V.
Run it on rechargeables and it’s much worse.
Given the low price, I’d expect these LEDs to fall over dead if I goosed them all to 20 mA… not to mention, 0.02 x 72 = 1.44 A is a pretty stiff load for alkalines and the housing wouldn’t stand up to nearly 9 W of power dissipation.
The Smell of Molten Projects in the Morning 