From 459d2c5630e1296807bbf23fd4360fb4d4f5bbe7 Mon Sep 17 00:00:00 2001
From: Paul Oliver <contact@pauloliver.dev>
Date: Fri, 12 Dec 2025 17:17:36 +0000
Subject: Adds basic I2C config and documentation

---
 README.md          | 45 +++++++++++++++++++++++++++++++++++++++++++++
 sysconf/config.txt |  3 ++-
 2 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index dbfbc28..9072edd 100644
--- a/README.md
+++ b/README.md
@@ -71,6 +71,51 @@ References:
 - [RPi Kernel Issue #6983](https://github.com/raspberrypi/linux/issues/6983)
 - [Libcamera Installation Guide](https://blog.jirkabalhar.cz/2024/02/raspberry-camera-on-archlinux-arm-in-2024/)
 
+## I2C Setup:
+The provided `config.txt` exposes `/dev/i2c-0` on GPIO pins 0 (SDA) and 1 (SCL).
+Ensure your user has I2C permissions:
+```console
+user@alarm$ sudo usermod ${USER} -aG i2c
+```
+
+Verify the interface works. Expected output (no devices yet):
+```console
+user@alarm$ sudo i2cdetect -y 0
+     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
+00:                         -- -- -- -- -- -- -- --
+10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+70: -- -- -- -- -- -- -- --
+```
+
+## Battery Monitoring with INA226
+This repository includes INA226 voltage/current sensing via I2C.
+For battery-powered operation:
+
+### Hardware Connections
+1. Battery terminals: V+/V- on INA226
+2. Load current path (Pi + motor controllers): I+/I- on INA226
+3. I2C lines: SDA/SCL (GPIO 0/1)
+4. 3V3 power and GND
+
+The INA226 should appear at address `0x40`:
+```console
+user@alarm$ sudo i2cdetect -y 0
+     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
+00:                         -- -- -- -- -- -- -- --
+10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+40: 40 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+70: -- -- -- -- -- -- -- --
+```
+
 ## Build Instructions:
 1. Install [`stack`](https://docs.haskellstack.org/en/stable/). It’s
    recommended to use [`ghcup`](https://www.haskell.org/ghcup/) for
diff --git a/sysconf/config.txt b/sysconf/config.txt
index f9ff6db..b2fdbc7 100644
--- a/sysconf/config.txt
+++ b/sysconf/config.txt
@@ -44,7 +44,7 @@ dtoverlay=disable-bt
 # Run as fast as firmware / board allows
 arm_boost=1
 
-# Set GPIO pins to output / low state on boot
+# Set GPIO pins to output/low state
 gpio=0-27=op,dl
 
 [cm4]
@@ -58,3 +58,4 @@ dtoverlay=dwc2,dr_mode=host
 
 [all]
 dtoverlay=pwm-2chan
+dtoverlay=i2c0-pi5
-- 
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