PICAXE temp / humidity

A gifted meter on acrylic — dusted off, connectors tidied, reading again.

Working unit showing Temp 22.4 C and Humid 71.5 percent — Front — Temp 22.4 °C, Humid 71.5 %

Story

Thank you to the young lady who gifted me this little meter. It had sat long enough to gather a soft grey coat of dust and lint — acrylic scratched, cells still in the holder, rocker left off. A kind handmade thing, and it deserved a cleanup rather than a drawer.

Dusty acrylic front: 1602 LCD, 3xAA pack, and rocker switch — As received — dust on the LCD, pack, and rocker

Back of the gifted unit: PICAXE 08M2 board with green jumper wires — As received — PICAXE 08M2+, green jumpers hard-wired into the loom

I took it apart, wiped the acrylic, and lifted the modules so each piece could be cleaned and checked on its own.

Cleanup

First the display — a QAPASS 1602 with a PCF8574 I2C backpack.

Front of the detached 1602 LCD module — LCD front — 16×2, cleaned

Back of the LCD with PCF8574 I2C backpack — LCD back — PCF8574 (GND / VCC / SDA / SCL)

Then the hand-etched controller — PICAXE 08M2+ in a socket, passives, and headers for power, bus, and sensor.

Component side of the PICAXE board — Component side — PICAXE 08M2+

Solder side of the hand-etched PICAXE board — Solder side — hand-etched copper

Put back together

On the way back I improved the wiring: the old fixed jumpers gave way to pin connectors so the LCD, sensor, and power loom unplug cleanly — no more re-soldering just to lift a module. Routes were shortened and dressed so the acrylic sandwich opens without fighting the harness.

Back after rewiring with connectors, red power LED on — After tidy-up — connectors, power LED on, AM2320 on the corner

Under the hood it is a small PICAXE 08M2+ talking I2C to the 1602 backpack and a four-pin temp/humidity sensor (AM2320-style: VDD / SDA / GND / SCL), running from 3×AA behind a rocker. This page stays light on firmware and focuses on the gifted build and the cleanup that brought it back.

Block diagram

Connections

Headers on the board feed power and a shared I2C bus — all on removable pin connectors after the tidy-up.

Power — switch only the positive lead:

3×AA +  ──► rocker switch ──► board V+
3×AA −  ────────────────────► board GND

LCD backpack (4-pin header on the PCF8574):

board GND ──► GND
board V+  ──► VCC
board SDA ──► SDA
board SCL ──► SCL

AM2320 (common order — confirm silkscreen):

board V+  ──► VDD
board SDA ──► SDA
board GND ──► GND
board SCL ──► SCL

The sensor pin order is easy to flip — match the module marking before powering. Headers stay removable so the panel, LCD, and sensor come apart without cutting wires.

Quick test

AM2320 pin order matches the silkscreen (not assumed from memory).
Fresh 3×AA fitted; rocker off, then on — power LED and LCD backlight should wake.
Display settles to Temp: / Humid: with plausible numbers (not stuck zeros).
Rocker off cleanly; nothing should get hot.