Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Kibitzing on a project involving an Arduino Mega (properly MEGA, but who cares?) with plenty of spare I/O pins led me to slap together a block of LEDs:
Arduino Mega Debugging LEDs
The excessive lead length on the 330 Ω resistors will eventually anchor scope probes syncing on / timing interesting program events.
Not that you have any, but they’re antique HP HDSP-4836 tuning indicators: RRYYGGYYRR. If you were being fussy, you might use 270 Ω resistors on the yellow LEDs to brighten them up.
A simple test program exercises the LEDs:
/*
Debugging LED outputs for Mega board
Ed Nisley - KE4ZNU
Plug the board into the Digital Header pins 34-52 and GND
*/
byte LowLED = 34;
byte HighLED = 52;
byte ThisLED = LowLED;
//-----
void setup() {
pinMode(LED_BUILTIN,OUTPUT);
for (byte p = LowLED; p <= HighLED; p+=2)
pinMode(p, OUTPUT);
// Serial.begin(9600);
}
// -----
void loop() {
digitalWrite(LED_BUILTIN,HIGH);
digitalWrite(ThisLED, HIGH);
delay(100);
digitalWrite(ThisLED, LOW);
// delay(500);
ThisLED = (ThisLED < HighLED) ? (ThisLED + 2) : LowLED;
// Serial.println(ThisLED);
digitalWrite(LED_BUILTIN,LOW);
}
Nothing fancy, but it ought to come in handy at some point.
The need to gnaw a V groove into the side of two 60 mm aluminum bars led to this Sherline CNC mill setup:
Sherline Y-Axis Nut Mishap – setup
Milling the near end of the bars put the angle plate’s rear lock screw within a millimeter of the column; the vise fits in exactly one spot on the angle plate and that’s where the jaws must be.
While controlling the mill with the Joggy Thing and some manual command entry, because it’s easier than real CNC programming, I overshot the near end and rammed the column with enough enthusiasm to dislodge the Y-axis leadscrew nut. An interlude of utter confusion ended with the backlash preload nut firmly jammed against the leadscrew coupler on the other end of travel:
Sherline Y-Axis Nut Mishap – stuck preload nut
The paper shreds show where the bellows formerly stuck on the Y axis stage.
The backlash nut chewed off a few star lock gear teeth on its way out, as seen here just above where they mesh:
Sherline Y-Axis Nut Mishap – chewed star nut
It’s been quite a few years since I took the thing apart to replace the nuts, so I used the opportunity to lube the otherwise inacessible X axis leadscrew inside its table upside down on the bench.
The setscrew locking the Y axis leadscrew nut in place heaves into view with the X axis table off:
Sherline Y-Axis Nut Mishap – setscrew
I thought about jamming it in place with a second 10-32 setscrew, but the ones on hand were just an itsy too long and collided with the X-axis table:
Sherline Y-Axis Nut Mishap – doubled setscrew
The thought of having the additional setscrew work loose, grind into the underside of the table, and require major surgery for recovery persuaded me to drop it back in the drawer.
With everything in place, I adjusted the backlash (on both axes) down to a few mils:
Sherline Y-Axis Nut Mishap – backlash test
Tweaking the X axis preload nut under the table is not my idea of a good time, but it’s been quite a while since I had to do that.
Folding the new paper bellows and installing them took about as long as repairing the mill.
Milling the second V groove worked fine; all is right with the Sherline again.
I noticed something out of place when I fired up the soldering iron:
Soldering Iron Spider
It’s not obvious in a flat photo without depth perception, but here’s a closer look:
Soldering Iron Spider – detail
A tiny spider had set up shop just over the tip cleaning port, with a delicate web linking the sponge to the iron holder.
I tried to deport her outdoors, as is our custom with helpful critters, but she jumped off the web and scurried to an unknown spot on the bench. She’ll surely rebuild in an equally productive spot.
Obviously, I’m not soldering enough electronic gadgetry …
The 15 Ω unswitched resistor sets the LED current at 53 mA = 0.8 V / 15 Ω, with the LED dissipating about 100 mW. The resistor dissipates 43 mW.
Closing the switch puts the two parallel 4.7 Ω resistors in parallel with the 15 Ω resistor to produce 2.0 Ω, which sets the LED current to 390 mA and runs it at 950 mW. Each of the 4.7 Ω resistors dissipates 140 mW.
That much power raises the aluminum body to 50 °C = 120 °F: definitely uncomfortable but probably survivable for the LED inside.
Eyeballometrically, a decimal order of magnitude difference in the LED current produces an obvious brightness difference. My first try ran the LED at 500 mW (a binary order of magnitude less than 1 W) and wasn’t visually different. Given that the LED will run from the Bafang’s headlight output, saving power isn’t all that important.
If this is the first time you’ve encountered parallel resistors, this is why your calculator has a reciprocal button: the total resistance is the reciprocal of the sum of the reciprocals of all the resistances:
A pleasant evening at a virtual Squidwrench meeting produced the raw shape of the front end from a 1 inch aluminum rod:
1 W LED Running Light – heatsink raw
Trace the outline of the LED’s PCB inside the cylinder just for comfort, align to the center, and drill two holes with a little bit of clearance:
1 W LED Running Light – heatsink drilling
For the 24 AWG silicone wire I used, a pair of 2 mm holes 8.75 mm out from the center suffice:
1 W LED Running Light – heatsink fit
Gnaw some wire clearance in the lens holder:
1 W LED Running Light – wiring
Tap the central hole for an M3×0.5 screw, which may come in handy to pull the entire affair together.
Epoxy the PCB onto the heatsink with the lens holder keeping it aligned in the middle:
1 W LED Running Light – heatsink clamp
Then see how hot it gets dissipating 900 mW with 360 mA of current from a 2.2 Ω resistor:
1 W LED Running Light – heatsink test
As you might expect, it gets uncomfortably warm sitting on the bench, so it lacks surface area. The first pass will use a PVC cylinder for easy machining, but a full aluminum shell would eventually be a nice touch.
A doodle with some dimensions and aspirational features:
Running Light – 1 W LED case doodle
Even without a lens and blinkiness, it’s attention-getting!
Being that type of guy, I turn my phone off during the night while it’s charging, turn it on for the next day’s adventures, and check the Google Play App Store to see which apps will get updates.
The vast machine learning / AI / whatever analyzing my every move still hasn’t figured out my morning ritual, so it desperately tries to sell me crap:
Google Play Store – app ad delay
My guess: those blank spots are placeholders for app ads, but, while the phone is busy scanning for malicious apps, the ad bidding process doesn’t complete fast enough to update the display before I see it.
FWIW, I had the Genuine NYS Covid-19 app installed for a while, but I very rarely go anywhere or see anybody, so it seemed to offer no net benefit.
The Smell of Molten Projects in the Morning 