Tour Easy 1 W Amber Running Light: Internal Plate

A semi-scaled doodle laying out an Arduino Nano and the MP1584 regulator board suggested they might fit behind the heatsink with the 1 W LED:

Amber running light - board layout doodle - side
Amber running light – board layout doodle – side

A somewhat more detailed doodle of the end view prompted me to bore the PVC pipe out to 23 mm:

Amber running light - board layout doodle - end
Amber running light – board layout doodle – end

The prospect of designing a 3D printed holder for the boards suggested Quality Shop Time combined with double-stick foam tape would ensure a better outcome.

So I bandsawed the remains of a chunky angle bracket into a pair of rectangles, flycut All The Sides to square them up, and tapped a pair of M3 holes along one edge of each:

1 W LED Running Light - baseplate tapping
1 W LED Running Light – baseplate tapping

The other long edges got the V groove that killed the Sherline’s Y axis nut:

Sherline Y-Axis Nut Mishap - setup
Sherline Y-Axis Nut Mishap – setup

The groove holds a length of 4 mm OD (actually 5/32 inch, but don’t tell anybody) brass tubing:

1 W LED Running Light - baseplate trial fit
1 W LED Running Light – baseplate trial fit

The M3 button head screws are an admission of defeat, as I could see no way of controlling the width + thickness of the aluminum slabs to get a firm push fit in the PVC tube. The screws let me tune for best picture after everything else settled out.

A little more machining opened up the top of the groove:

1 W LED Running Light - baseplate dry assembly
1 W LED Running Light – baseplate dry assembly

A short M3 button head screw (with its head turned down to 4 mm) drops into the slot and holds the slab to the threaded hole in the LED heatsink. The long screw is holding the threaded insert in place for this dry fit.

I doodled a single long screw through the whole thing, but having it fall off the heatsink when taking the rear cover off seemed like a Bad Idea™. An M3 button head screw uses a 2 mm hex key that fits neatly through the threaded insert, thereby making it work.

Butter it up with epoxy, scrape off the excess, and let things cure:

1 W LED Running Light - baseplate curing
1 W LED Running Light – baseplate curing

This was obviously made up as I went along …

Arduino MEGA Debugging LEDs

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
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.

Soldering Iron Spider

I noticed something out of place when I fired up the soldering iron:

Soldering Iron Spider
Soldering Iron Spider

It’s not obvious in a flat photo without depth perception, but here’s a closer look:

Soldering Iron Spider - detail
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 …

Running Light: 1 W LED Switched Parallel Resistors

Manually selecting the current through the 1 W amber LED with a switch actually intended for LED flashlights:

1 W LED Running Light - switched parallel R
1 W LED Running Light – switched parallel R

The resistors on the low side of the LED use the MP1584 regulator for current control, with the orange wire feeding the resistor voltage into the error amplifier.

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:

1/R = 1/R₁ + 1/R₂ + …

A real engineering calculator does not have a shifted reciprocal function.

Running Light: 1 W LED Heatsink

The general idea: a cylindrical holder / heatsink for a 1 W LED on the end of a tube clamped in a Tour Easy fairing mount, much like a flashlight.

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
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
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
1 W LED Running Light – heatsink fit

Gnaw some wire clearance in the lens holder:

1 W LED Running Light - wiring
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
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
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
Running Light – 1 W LED case doodle

Even without a lens and blinkiness, it’s attention-getting!

MP1584 Current Regulator: Arduino Blinkiness

Mostly because I wanted to verify that it really worked:

MP1584 current - red LED - Arduino blinkiness
MP1584 current – red LED – Arduino blinkiness

The Arduino Nano runs the default Blink program that all the knockoff manufacturers use as their final QC test.

The MP1584 specs say the Enable input can accept a logic signal up to 6 V, the Nano runs at 5 V regulated down from the 6.3 V from the bench supply, and the 1 W red LED now flashes 1 s ON / 1 s OFF.

The current feedback works as it did before, too, which is comforting.

The Nano adds 20 mA to the bench supply, so the whole affair runs at 220 mA = 1.4 W. Of course, it’s now at a 50% duty cycle, so that helps.

I doubt hand-hewing an astable multivibrator is the right way to add blinkiness, but it’d definitely be playing on hard mode.

MP1584 Current Feedback: 1 W Red LED

A red 1 W LED works just as well as the amber LED from an MP1584 regulator hacked into current feedback mode:

MP1584 buck regulator - current feedback - red LED
MP1584 buck regulator – current feedback – red LED

I started with the same 1.65 Ω sense resistor and got the same 484 mA current, with the LED forward drop at a surprisingly high 3.3 V = 1.6 W. Ouch.

Adding a 1 Ω series resistor to get 2.65 Ω lowered the current to 300 mA with a forward drop of 2.45 V = 740 mW.

Running the numbers suggested a 2.3 Ω sense resistor made from a pair of parallel 4.7 Ω resistors, which produced 346 mA and an LED drop of 2.66 V = 920 mW. The resistor dissipates 280 mW.

The bench supply provides 6.3 V @ 200 mA = 1.26 W, so the overall efficiency is 94% and the LED burns 73% of the input.

I expected the red LED would have a lower forward drop than the amber LED, but it’s actually higher.

Word: Trust, but verify.