Electronics | Tomokatsu Yukishita | yre.jp

Raspberry Pi 3 + Official 7-inch Touchscreen Photo Frame with Ambient Light Sensor Auto-Brightness (BH1750FVI + I2C + Python)

Tue, 19 Jul 2022 00:00:00 +0000

After building a cloud-connected photo frame with Raspberry Pi 4, I had a spare Raspberry Pi 3 and official 7-inch touchscreen sitting around. I turned them into another photo frame — and added a GY-30 BH1750FVI ambient light sensor to automatically adjust display brightness based on the room’s lighting.

Hardware

Raspberry Pi 3

Raspberry Pi 3 Model B Single-board Computer

Amazonで見る

Official 7-inch Touchscreen

800×480px, 24-bit RGB color, 60 fps, up to 10-point multitouch.

Raspberry Pi Official 7-inch Touchscreen LCD

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Case for the Official Touchscreen

Designed to house both the Raspberry Pi 3 Model B and the 7-inch display.

Raspberry Pi & 7-inch LCD Touchscreen Case ABS (RS Components, Black)

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Connecting the Display

Follow the Raspberry Pi Touch Display official documentation to assemble the display.

When connecting, pay attention to the ribbon cable orientation. For the power wires, connect red to the 5V pin and black to the GND pin.

Display Rotation Setting

By default the display is rotated 180°. The fix depends on your OS version.

The lcd_rotate=2 option below is for Raspberry Pi OS Bullseye and earlier (legacy/FKMS mode). On Bookworm (2023 and later), lcd_rotate is not officially recommended — use the Screen Configuration GUI tool instead.

The config file path also differs by OS version:

Bullseye and earlier: /boot/config.txt
Bookworm and later: /boot/firmware/config.txt

For Bullseye and earlier (legacy/FKMS mode):

sudo vi /boot/config.txt

Add the following line:

lcd_rotate=2

Slideshow Program

The slideshow uses the Python script from the cloud-connected photo frame project (photoView4).

Display Brightness Control

Running the display at full brightness all the time is uncomfortable in a dark room. The official 7-inch display allows brightness control by writing a value (0–255) to a sysfs file:

echo "100" | sudo tee /sys/class/backlight/rpi_backlight/brightness

Adding an Ambient Light Sensor (BH1750FVI)

Rather than setting brightness manually, I wanted it to adjust automatically based on ambient light.

Parts

WINGONEER GY-30 BH1750FVI Digital Light Intensity Sensor Module I2C for Raspberry Pi

Amazonで見る

ELEGOO 120pcs Dupont Jumper Wires Male-Female / Male-Male / Female-Female Set

Amazonで見る

Connecting to Raspberry Pi via I2C

The BH1750FVI communicates over I2C. Refer to the Raspberry Pi GPIO pin layout for wiring.

Raspberry Pi GPIO pinout (source: Raspberry Pi official documentation)

Wiring Table

Raspberry Pi	GPIO Pin	BH1750FVI
GPIO2 (SDA)	3	SDA
GPIO3 (SCL)	5	SCL
5V Power	2	VCC
Ground	14	ADO
Ground	20	GND

BH1750FVI wired to Raspberry Pi 3 via I2C

Verifying the Sensor (Python)

After wiring, confirm data is coming through. Based on a reference implementation on GitHub:

#!/usr/bin/python3

import smbus

Bus = smbus.SMBus(1)
Addr = 0x23
LxRead = Bus.read_i2c_block_data(Addr, 0x11)
print("Illuminance: " + str(LxRead[1] * 10) + " lx")
LxRead2 = Bus.read_i2c_block_data(Addr, 0x10)
print("Brightness: " + str((LxRead2[0] * 256 + LxRead2[1]) / 1.2))

Running it confirms the sensor is working:

root@raspi3-photo:~# python br.py
Illuminance: 1650 lx
Brightness: 990.8333333333334

Auto-brightness Control Program

The final program adjusts backlight brightness smoothly based on ambient light readings:

Target brightness levels are defined per illuminance range
The display brightness is incremented or decremented one step at a time toward the target
The I2C sensor is polled every 300ms — polling faster than this results in incorrect readings with SMBus

Sensor Placement

The sensor is mounted on the protruding back section of the case, where it receives ambient light from the room.

Sensor mounted on the case back where it can see ambient light

Source Code

The complete program (object-oriented version) is on GitHub:

GitHub - yukishita/lcdBrightness2: Auto-brightness control for Raspberry Pi official display using BH1750FVI light sensor

Demonstration

The brightness adjusts smoothly as ambient light changes:

Summary

Component	Role
Raspberry Pi 3	Main computer
Official 7-inch Touchscreen	Photo frame display (800×480px)
GY-30 BH1750FVI	I2C ambient light sensor
Python (smbus)	I2C communication and brightness control logic

Adding the light sensor makes the photo frame genuinely pleasant to use — bright during the day, dimmed at night, automatically.

DIY JJY Simulator with ATOM Lite: Sync a Radio-Controlled Clock Without a Signal

Thu, 12 May 2022 00:00:00 +0000

After moving to a new home where my radio-controlled clock could no longer receive the JJY time signal, I built a low-cost JJY simulator using an M5Stack ATOM Lite and a JJY antenna board. This is a record of how I solved the problem for well under JPY 5,000.

The Problem: Radio-Controlled Clock Stopped Syncing After Moving

Radio-controlled clocks are convenient precisely because they set themselves automatically. After moving, however, my clock stopped receiving the JJY signal indoors, and the displayed time slowly drifted out of sync.

The clock could still pick up the signal near a window, but carrying it there and back every time it needed syncing was not a practical long-term solution.

What Is JJY?

JJY is the call sign for Japan’s standard time radio signal, broadcast by the National Institute of Information and Communications Technology (NICT). Two transmitters cover the country: 40 kHz from Fukushima (Ōtakadoya-yama) and 60 kHz from Saga (Haganeyama). Radio-controlled clocks receive this signal to maintain accurate time automatically.

The device described in this article simulates the JJY signal and rebroadcasts it locally, allowing a clock to sync even when it cannot receive the real transmission.

Commercial Retransmitters Are Expensive

There are commercial products designed to solve exactly this problem — they receive accurate time from NTP servers or GPS and retransmit a JJY-compatible signal indoors.

Kyohritsu Denshi AC-Synchronized Time Transmitter P18-NTPAC

Amazonで見る

KEISEEDS GPS Radio Clock Repeater P18-NTPGR

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Radio Clock Signal Transmitter with Built-in Clock P18-NTPLR

Amazonで見る

These products work well, but they typically cost JPY 10,000–30,000. Hard to justify for a single clock at home.

The DIY Solution: ATOM Lite + JJY Antenna Board

Searching Switch Science (a Japanese electronics parts retailer), I found a JJY antenna board designed to work with M5Stack devices — exactly what I needed.

Required Parts

Product	Link	Notes
JJY antenna board for M5StickC	Switch Science	M5StickC specific
JJY antenna board for M5Atom	Switch Science	For ATOM Lite/Matrix
M5StickC	Switch Science	Discontinued
ATOM Lite	Switch Science	Available now — recommended
ATOM Matrix	Switch Science	Available now

Note: M5StickC has been discontinued. For new builds, the recommended combination is ATOM Lite with the JJY antenna board for M5Atom. The original article used M5StickC, which is what appears in the photos below.

At the time of purchase, the antenna board and M5 device together came to under JPY 5,000 (prices may vary — check current listings before ordering). That is roughly one-third to one-sixth the cost of a commercial retransmitter.

Setup

Setup follows the instructions in the GitHub repository linked from the Switch Science product page:

Flash the firmware following the instructions and there are no unusual steps. It worked on the first attempt without any issues.

Testing

With the firmware flashed, connect the M5 device to the JJY antenna board and place it next to the radio-controlled clock.

Place the device right next to the clock to receive the simulated signal

The transmitted signal is weak and short-range. The device needs to be within a few centimeters to a few tens of centimeters of the clock to sync reliably. In practice this is not a problem — once the clock has synced, it holds accurate time on its own until the next sync cycle.

Known Limitation

One issue worth noting: if the device is used near a microwave oven, the Wi-Fi connection drops and does not automatically reconnect. A manual restart is required. Either keep the device away from the microwave, or add a periodic auto-reset to the firmware.

Summary

Item	Detail
Total parts cost	Under JPY 5,000 (roughly 1/3–1/6 of commercial alternatives)
Soldering required	None
Setup difficulty	Low — flash firmware from GitHub and place next to clock
Signal range	Short (a few cm to a few tens of cm)
Known issue	Wi-Fi drops near microwave, requires manual restart

A practical and affordable way to keep a radio-controlled clock synced in a room with poor JJY reception. If you are in a similar situation, this combination is well worth trying.