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Set up of Open Rowing Monitor

This guide roughly explains how to set up your device. I will probably build an automated installation script from this later.

Requirements

A Raspberry Pi that supports Bluetooth Low Energy (Pi 3 or Pi 4). Probably this also runs on other devices.
An SD Card, any size above 4GB should be fine
A rowing machine (obviously) with some way to measure the rotation of the flywheel
- the WRX700 has a build in reed sensor that I can directly connect to the GPIO pins of the Raspberry Pi
- if your machine doesn't have a sensor, it should be easy to build something similar (magnetically or optical)
Some Dupont cables to connect the GPIO pins to the sensor

Software Installation

Set up the Raspberry Pi

Install Raspberry Pi OS Lite on the SD Card i.e. with the Raspberry Pi Imager
Connect the device to your network (headless or via command line)
Enable SSH

Open a SSH-Connection and set up the dependencies

sudo apt-get update
sudo apt-get dist-upgrade
sudo systemctl disable bluetooth
sudo apt-get install bluetooth bluez libbluetooth-dev libudev-dev

Install Node.js

curl -fsSL https://deb.nodesource.com/setup_14.x | bash -
apt-get install -y nodejs

If you want to run Bluetooth Low Energy and the webserver on port 80 without root

sudo setcap cap_net_bind_service,cap_net_raw=+eip $(eval readlink -f `which node`)

Download Open Rowing Monitor and install dependencies

curl -LJO https://github.com/laberning/openrowingmonitor/archive/main.zip
unzip main.zip -d ~/openrowingmonitor
rm main.zip
cd ~/openrowingmonitor
npm install

Configuration and Startup

You should now be able to start the Rowing Monitor: npm start

You should now adjust the rower specific parameters in app/engine/RowingEngine.js to suit your rowing machine.

Automatically start Open Rowing Monitor while booting

Create file /lib/systemd/system/openrowingmonitor.service with the following content:

[Unit]
Description=Open Rowing Monitor
After=multi-user.target

[Service]
Type=simple
User=pi
# Restart=on-failure
WorkingDirectory=/home/pi/openrowingmonitor
ExecStart=/bin/bash -c 'PATH=/home/pi/.nvm/versions/node/v14.15.5/bin:$PATH exec npm start'

[Install]
WantedBy=multi-user.target

Hardware Installation

Basically all that's left to do is hook up your sensor to the GPIO pins of the Raspberry Pi.

Open Rowing Monitor reads the sensor signal from GPIO port 17 and expects it to pull on GND if the sensor is closed. To get a stable reading you should add a pull-up resistor to that pin. I prefer to use the internal resistor of the Raspberry Pi to keep the wiring simple but of course you can also go with an external circuit.

Internal wiring of Raspberry Pi

The internal pull-up can be enabled as described here. So its as simple as adding the following to /boot/config.txt and then rebooting the device.

# configure GPIO 17 as input and enable the pull-up resistor
gpio=17=pu,ip

How to connect this to your rowing machine is specific to your device. You need some kind of mechanism to convert the rotation of the flywheel into impulses. The WRX700 has a reed sensor for this built-in so hooking it up is as simple as connecting the cables. This sensor had one magnet on the wheel, which gives one impulse per rotation. I simply plugged a second magnet to the opposite side of the wheel to double the resolution for more precision.

Connecting the reed sensor

If your machine does not have something like this or if the sensor is not acessible, you can still build something similar quite easily. Some ideas on what to use:

Reed sensor (i.e. of an old bike tachometer)
PAS sensor (i.e. from an E-bike)
Optical chopper wheel

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