Nest box door

Electricity behaves a lot like water in pipes. Every word below has a water version. Click any card for the longer story.

👆 Click any part: the battery, the fuse, each board, the resistors, and even the long black ground wire.

Read this once and the diagram stops looking like spaghetti. Power flows from left to right. Signals flow from the brain outwards.

1. The battery pushes

   The sealed lead-acid battery pushes at about 12 volts. The fuse sits in the red lead. If a wire ever shorts, the fuse melts and the battery cannot start a fire.

2. The 12 V line feeds three things

   After the fuse, the red wire is called the +12 V line. It feeds the buck, the motor driver's POWER terminal, and the top of the battery sense divider.

3. The buck makes 5 V for the brain

   The buck converter takes 12 V in and gives a steady 5 V out. The XIAO board needs 5 V. Feed it 12 V and it dies instantly.

4. The brain asks the clock what time it is

   The XIAO ESP32-C3 is a tiny computer. It talks to the clock module over two wires, SDA and SCL. From the date and your latitude it works out today's sunrise and sunset.

5. The brain tells the driver to move

   When it is time, the XIAO raises one of two signal pins, IN1 or IN2. The motor driver sees that and connects the battery's full 12 V to the actuator, in one direction or the other.

6. The brain keeps an eye on the battery

   All day, the XIAO peeks at the battery voltage through the battery sense divider. When the battery drops below 11.9 V, the code parks the boxes open and stops moving. A flat battery therefore never locks the hens out.

The same content as the diagram pop-ups, laid out to read straight through. Green text marks a pin you use. Red text marks a pin that must stay empty.

Seeed XIAO ESP32-C3, the brain

It measures 21 × 17.8 mm. The USB-C socket sits at the top. The pin names are printed on the underside.

Pin	GPIO	Goes to
D0	GPIO2	LEAVE EMPTY. It is a strapping pin.
D1	GPIO3	driver IN1
D2	GPIO4	the sense node of the battery divider
D3	GPIO5	driver IN2
D4	GPIO6	clock SDA
D5	GPIO7	clock SCL
D6	GPIO21	spare
5V	—	buck VOUT
GND	—	the ground spine
3V3	—	clock VCC
D10	GPIO10	spare
D9	GPIO9	LEAVE EMPTY. It is the boot button.
D8	GPIO8	LEAVE EMPTY. It is a strapping pin.
D7	GPIO20	spare

The three red pins

The chip reads D0, D8 and D9 at the instant it powers up to decide how to boot. A resistor to ground on any of them stops the board from starting. That is why IN1 and IN2 go to D1 and D3 rather than the obvious D0 and D1.

Photo: Seeed Studio wiki

Adafruit DRV8871, the motor driver

Read the printed labels in the photo. The MOTOR block has screws 2 and 1. The POWER block has + and −. Four header holes run along the bottom edge.

Terminal or pin	Goes to	Solder?
POWER +	the +12 V line, from the fuse	No. It is a screw terminal.
POWER −	ground spine	No. Screw terminal.
MOTOR 1	actuator wire A	No. Screw terminal.
MOTOR 2	actuator wire B	No. Screw terminal.
IN2	XIAO D3	Yes
IN1	XIAO D1	Yes
VM	Skip it. The POWER terminal already feeds it.	No
GND	ground spine, plus one leg of each 10 kΩ pull-down	Yes

Good news

The green screw terminals arrive already soldered on. The two connections that carry the most current therefore need no soldering iron at all.

Photo: Adafruit Learning System

Pololu D36V6F5, the 5 V buck

It measures 10 × 13 mm. The coin in the photo is a US quarter. The names are printed on the underside, which is the face shown here.

Pad	Goes to
VOUT	XIAO 5V
GND	ground spine
VIN	the +12 V line, from the fuse
SHDN	Leave it empty.

Read this order twice

Left to right the pads read VOUT · GND · VIN · SHDN. VIN and VOUT sit two pads apart with ground between them. Swap them and 12 V goes straight into the XIAO. Measure VOUT with the meter before you connect the XIAO.

Photo: Pololu

DFRobot DS3231M, the clock

It measures 22.5 × 21 mm. A CR1220 coin cell sits on the reverse. Seven pads run in one row.

Pad	Position	Goes to
VCC	1st	XIAO 3V3
GND	2nd	ground spine
SCL	3rd	XIAO D5
SDA	4th	XIAO D4
INT	5th	not used
RST	6th	not used
32K	7th	not used

SCL comes before SDA

Most clock modules print them the other way round. If you wire it from habit you will swap them, and the clock will simply not answer.

Photo: DFRobot, DFR0641

Four resistors, one capacitor and one fuse. They come in a bag with no names printed on them, so this is where beginners get lost. Match the coloured bands to the pictures. Click any picture for the full explanation.

You need two types of wire, and the difference matters. The thin wire carries only tiny signals. The thick wire carries the current for the motor.

Everything that ends up in the finished controller. The tools you need to assemble it are in the next section. Prices were checked on 15 September 2026 and the ≈ sign means close but not verified.

These are the things you use to build it rather than things that end up inside it. Skip any you already own. There are two ways to buy: you can walk into Jaycar today, or wait a few days and pay less at Amazon. Prices and ratings were checked on 15 September 2026. The ≈ sign means close but not verified. Bold marks the better buy.

Practise on the spare half of the experimenters board first. Twenty throwaway joints and you will have it.

1. Set the iron to 350 °C and wet the sponge

   Do not go hotter. Hotter does not make it faster. Hotter lifts the copper pads off the board.

2. Tin the tip

   Melt a little solder onto the tip and wipe it on the sponge. It should look bright silver. A dull grey tip transfers almost no heat, so re-tin it every few joints. This is called tinning.

3. Heat the metal, not the solder

   Press the tip against the pad and the pin at the same time. Count to two.

4. Feed solder into the joint, not onto the iron

   Touch the solder to the far side of the pin, away from the tip. It should run around the pin and wrap it in half a second.

5. Take the solder away first, then the iron

   Hold everything still for three seconds. If you move it while it sets, you get a grainy joint that fails in the coop.

6. Look at it

   A good joint is shiny and cone-shaped, like a tiny volcano hugging the pin. A dull ball sitting on top is a cold joint. Reheat it until it collapses and flows.

The wiring diagram tells you what connects to what. This tells you where to physically put it. The board is a 70 × 90 mm perfboard, which is 35 holes across and 27 down. It must be the plain kind, where no hole connects to any other. Stripboard, which links whole rows together, would short this layout out. Holes are named like a map: column letter, then row number. M10 is column M, row 10.

Never wire the whole thing and then switch it on. Add one board, test it, then add the next. A fault is then always in the thing you just touched.

1. Solder headers onto all four boards. Do nothing else yet.

   Set the meter to continuity. Check that every pin connects to its own pad and not to its neighbour.

2. Power the buck on its own

   Connect battery → fuse → VIN and GND. Put the meter across VOUT and GND. It must read 5.0 V ± 0.1. If it reads 12 V, you have VIN and VOUT swapped, and you have just saved your XIAO.

3. Add the XIAO

   Connect VOUT → 5V and GND → GND. Upload the Blink program. If the light blinks, the power chain works.

4. Add the clock

   Connect 3V3, GND, SDA and SCL. Print rtc.now() to the Serial monitor. If the time counts up, the two clock wires are right.

5. Add the divider

   Fit the 220 kΩ, the 33 kΩ and the 100 nF. Compare what batteryVolts() prints against the meter on the battery, then set VBAT_CAL.

6. Add the driver and actuator, on the bench, not on the door

   Fit both pull-downs. Set TEST_MODE to true. Run ten open-and-close cycles before it goes anywhere near the coop.

7. Now mount it

   Use an IP65 box under cover with the cable glands pointing down. Put the battery in a ventilated crate below the box, on spade terminals.

Twenty-three connections. Tick each one as you make it. The ticks stay saved in this browser.

Clear all ticks

The same explanations that pop up when you click a word, laid out to read straight through. Grouped by topic, not alphabetically, so the basics come first.