The Almanac

The Almanac

Field notes & findings of Elijah

Vol. I · Hobart, Tasmania
Begun 11 · X · 2026 ·

Entry No. 00111 October 2026Subject: Electronics

Mini Radar

What we're making

A mini radar. A servo motor swings an ultrasonic sensor from side to side, and the Arduino draws whatever it finds on a little screen.

Versions V1 → V2

V1

Pico radar

Raspberry Pi Pico swinging the sensor, with a retro CRT-style radar drawn in Processing on the PC.

  • Big screen, so loads of detail
  • Red blips that clump together and estimate size
  • Needs the laptop plugged in to see anything
  • Not a standalone gadget
V2

Mini radar 11 Oct 2026

Shrunk down onto an Uno kit with its own 1.3" OLED screen. The build on this page.

  • Works on its own, no laptop needed
  • Kit parts, easy to build step by step
  • Tiny one-colour screen, so less detail
  • Only clear for about 40 cm around it

How it works sketch I

  1. The ultrasonic sensor uses echolocation to estimate distances.
  2. The servo is the movement. You tell it an angle and it goes exactly there.
  3. The screen is the map. Angle + distance = a dot on a half circle.

test every part on its own first!

angle distance dot = something found! ~40 cm servo + sensor fig. i: what the screen shows

Parts

  • Arduino Uno (the brain)
  • USB cable
  • Breadboard
  • Servo motor
  • Wires
  • Ultrasonic sensor
  • Screen
  • Blu-Tack or hot glue
  • A laptop with Arduino IDE
Step 1

Laptop prep

  1. Install Arduino IDE arduino.cc/en/software
  2. Plug in the Arduino Uno.
  3. Tools → Board → Arduino Uno
  4. Tools → Port → pick the COM port that showed up.
  5. Tools → Manage Libraries → search U8g2 → Install.
TestFile → Examples → 01.Basics → Blink, then upload. The little L light on the board should start blinking.
Step 2

Screen

Power first: Uno 5V → red (+) rail, Uno GND → blue (−) rail. Everything gets power from these 2 rails.

ArduinoUno 5VGND (+) red rail (−) blue rail screen sensor servo

Screen wiring

  • GND(−) rail
  • VCC(+) rail
  • CLKpin 13
  • MOSIpin 11
  • RESpin 7
  • DCpin 8
  • CSpin 10
TestRun test2.ino. It should show "Hello!", a border and a circle.
Step 3

Distance sensor

Use male-to-female wires so the sensor can move around later on the servo motor.

Sensor wiring

  • VCC(+) rail
  • GND(−) rail
  • Trigpin 5
  • Echopin 6
TestRun test3.ino. Open Tools → Serial Monitor and set it to 9600 baud (bottom right). Move your hand in front and watch the numbers change.
Step 4

Servo motor

Servo wiring

  • Black wire(−) rail
  • Red wire(+) rail
  • Yellow wirepin 3
TestRun test4.ino. The motor should move back and forth.
Step 5

Sensor + servo

Centre the servo with test5.ino. Then put the plastic arm and sensor together with hot glue or Blu-Tack, attach the servo to something to stop it wobbling, and clear an area of about 40 cm radius.

Step 6

The full radar

Keep the wires like they are. Upload fullv2.ino.

If something's wrong

  • Check wiring
  • Change values
— E.entry I
Entry No. 00211 October 2026Subject: Electronics

Colour Mixer

Mix colours on the RGB colour matrix with a joystick. Push down to add blue.

Versions V1 → V1

V1

Joystick mixer 11 Oct 2026

Joystick mixes the colour on the RGB light, push down for blue.

  • Simple, only 9 wires
  • Instant feedback, fun to play with
  • Blue comes from the joystick button, which is only on or off, so it can't fade smoothly

The circuit sketch I

Joystick ArduinoUno RGB VRx→A1 VRy→A2 SW→2 3→R 5→G 6→B push down = add blue colours mix in the light fig. i: stick in, colour out

Wiring

RGB wiring

  • Rpin 3
  • Gpin 5
  • Bpin 6
  • (−)(−) rail

Joystick wiring

  • GND(−) rail
  • +5V(+) rail
  • VRxA1
  • VRyA2
  • SWpin 2

Run it

Upload ColourMixer.ino.

— E.entry II
Entry No. 00322 October 2026Subject: Chemistry & build

The Arc Reactor Cell

Turns out if you run electricity through water it splits into hydrogen & oxygen. Found this out today and now I want to build one. Research first, then I design my own cell that looks like Iron Man's arc reactor.

Versions V1 → V3

V1

Pencil-lead test jar 22 Oct 2026

A 9 V battery and two pencil leads in a jar of water and baking soda.

  • Costs nothing, takes 10 minutes
  • Shows the 2 : 1 bubbles straight away
  • Both gases come up in the same jar
  • Pencil leads crumble after a while
V2

Arc Reactor Cell 22 Oct 2026

Printed arc-reactor housing: steel centre, 10 graphite rods, separator, each gas out its own tube.

  • Gases stay separate the whole way out
  • Graphite rods last, and it looks like an arc reactor
  • Needs printing, sealing and an overnight leak test
  • More parts to buy
V3

Show mode 22 Oct 2026

Adds a current sensor, power-up light sequence, OLED readout and glowing bubble columns. See the 3D model →

  • Glow and pulse follow the real current
  • Looks amazing to people who don't know how it works
  • More electronics to wire (Pico, INA219, OLED)
  • Only exists as a 3D model so far
Part oneResearch notes

The apparatus sketch I

2H₂O → 2H₂ + O₂
2 vol. 1 vol. H₂ ( − ) O₂ ( + ) water + pinch of baking soda 9 V fig. i: the upturned-tube cell

H₂ side fills up TWICE as fast!!

That's the "2" in 2H₂ actually happening. If you count the bubbles the − side is way busier.

Ratios hydrogen : oxygen

By volumeas gas, same temp
H₂ · 2O₂ · 1
2 : 1
By mass4 g H₂ per 32 g O₂
H₂O₂ · 8 parts
1 : 8
From 1 kg waterwhat comes out
112 g888 g O₂
1 kg

checked it: 2 × 2 g = 4 g vs 32 g → 1 : 8 ✓ yep

Power required Faraday's law

Each H₂ needs 2 electrons to make. A mole of electrons is 96,485 coulombs (that's Faraday's constant, F), so that's how you work out how much power it takes.

Q = n · z · F = 1 × 2 × 96,485 ≈ 193,000 C per mole of H₂
1 amp, 1 hour
3,600 C
≈ 0.019 mol of H₂
Gas collected
0.45 L
of H₂, plus 0.22 L of O₂
Least voltage
1.23 V
but really you need 1.8–2 V
1 kg of H₂
39 kWh
on paper · more like 50–55 kWh for real

The rocket secret why engines run fuel-rich

This is the cool bit. You'd think rockets burn it at the perfect 8 : 1, but they actually use less oxygen on purpose.

Perfect burn

8 : 1

Uses up all the fuel, but the exhaust is all heavy water vapour.

Shuttle RS-25

~6 : 1

The leftover H₂ makes the exhaust lighter so it shoots out faster. About 450 s of specific impulse in space.

→ so electrolysis actually makes MORE oxygen than the rocket even wants!

Part twoDesigning the reactor

The idea

So the plan is an electrolysis cell shaped like an arc reactor. The middle is the − side and makes the hydrogen. The ring of 10 segments around it is the + side and makes the oxygen. Then LEDs behind it light up all the bubbles.

the arc reactor already has a middle + a ring around it. that's literally 2 electrodes!

Front view sketch II

steel cathode (−)makes H₂ separator ringcoffee filter on a printed frame 10 graphite anodes (+)make O₂ 12 LEDs behindthe glowing rim fig. ii: front view, Ø100 mm chamber

Keeping the gases apart sketch III

Most important part. The separator lets water and current through but keeps the bubbles on their own side. Each gas gets its own tube going into its own cup of water, so I can watch it bubble out and they never meet.

(−)(+) H₂ bubbler O₂ bubbler H₂ tube, from inside the separator O₂ out LED ring + clear back clear front window separator water + baking soda small air gap at top fig. iii: side cut (depth stretched)

if the H₂ cup bubbles twice as fast as the O₂ cup = it works

Design numbers

Chamber
Ø100 mm
× 30 mm deep ≈ 235 mL of water
Power
5 V USB
through a 5 Ω, 2 W resistor, aiming for about 0.5 A
H₂ at 0.5 A
3.8 mL/min
≈ 0.23 L an hour
O₂ at 0.5 A
1.9 mL/min
always half of the H₂

How much current you actually get depends on how much baking soda goes in. That's what the mixing table is for.

0.5 A ÷ (2 × 96,485) × 24.5 L/mol × 60 ≈ 3.8 mL/min of H₂

Mixing the water ingredient ratios

Plain water barely conducts, so you add a bit of baking soda (sodium bicarbonate). Going for 2% by weight, which is 20 g per litre of distilled water.

  • Batchwater : baking soda
  • Pencil-lead test jar100 mL : 2 g (½ tsp)
  • Reactor fill220 mL : 4.5 g (1 tsp)
  • Big batch to keep1 L : 20 g (4 tsp)
  • Each bubbler cup150 mL : none
  1. Start at half strength (1 g per 100 mL) and check the current with the multimeter.
  2. Add a pinch at a time until it says 0.3–0.5 A, then stop.
  3. Stir till it's totally clear before filling, or the leftover bits clog the filter.

1 level tsp of baking soda ≈ 4.5–5 g

At 0.5 A it only uses up about 0.17 g of water an hour, so one fill should last weeks. When it gets low, top up with just distilled water, NOT more soda (the soda doesn't get used up).

Measurements sketch IV

140 mm Ø140 outerhousing ring, PETGØ127 LED circle12 LEDs, 40 cm of strip6 × M3 on Ø112bolts clamp the discsØ100 chamber30 mm deep10 rods on Ø76graphite Ø5 × 40, 36° apartØ30 separatorprinted cage + coffee filterM6 × 40 boltstainless, the centre (−) fig. iv: measured front, to scale

Body

  • Housing ringØ140 / Ø100 × 30
  • Front + back discsØ140 × 3 acrylic
  • Bolts6 × M3 × 40
  • Water fill220 mL (5 mm gap)

Electrodes

  • Centre (−)M6 × 40 steel
  • Ring (+)10 × Ø5 × 40 graphite
  • In the water25 mm each
  • SeparatorØ30 × 28 deep

Gas + light

  • Tubing4 mm ID, 2 × 30 cm
  • Tube under water2–3 cm
  • LED strip30 LED/m, 40 cm
  • Resistor5 Ω, 2 W

Worked out the graphite ring has about 8 times more area in the water than the middle bolt (3,930 mm² vs 471 mm²). The + side slowly wears away, so more area means the rods last way longer.

Print the ring in see-through PETG and put the LED strip behind it at Ø127. Then the whole rim glows like the real arc reactor.

Parts

  • Housing ring, 3D printed in translucent PETG
  • 2 clear acrylic discs, Ø140 × 3 mm
  • 6 × M3 × 40 bolts + nuts
  • Silicone sealant or O-rings
  • M6 × 40 stainless bolt (− side)
  • 10 plain graphite rods, Ø5 × 40 mm (+ side, not copper-coated)
  • Coffee filter + printed frame (separator)
  • 2 barbed fittings + 60 cm of 4 mm silicone tubing
  • 2 cups of water (bubblers)
  • 40 cm of 30 LED/m NeoPixel strip (12 LEDs) + Pico
  • 5 V USB supply + 5 Ω 2 W resistor
  • Distilled water + baking soda + a multimeter

Use graphite on the + side, NOT steel. The + side eats away whatever metal is on it, and stainless steel can leak nasty chromium into the water. Same goes for copper and solder, keep them out of the water.

Build steps

DangerNever join the two tubes or let the gases mix. Mixed H₂ + O₂ explodes.
No flames or sparks near the cups. Don't block the tubes or try to store the gas.
Run it by an open window and unplug it when I walk away.
— E.entry III