willem.com

Sensors on Willem's Blog

Developing a native iOS app

Making a cycling and running tracker

May 11, 2024
How hard can it be to build your own cycling and running workout tracker app using native code with some help from AI? Read along to find out!

As a little side-project, squeezed between my normal work, I have been working on something of personal interest: a native workout tracking app for iOS. I wanted to make my smartwatch obsolete, instead using my phone to track workouts. How hard could it be to gather detailed sensor data using native Swift APIs?

Impact of training

Analysing WHOOP's trend data

May 31, 2023
Join me on an intriguing journey as I explore the transformative impact of effective training and data analysis on my performance in the Fietselfstedentocht 2023.

This Monday I completed 235KM on my fixed gear bike during the Fietselfstedentocht 2023. It was a nice ride with fair weather and favourable wind conditions. Yet, I took the challenge seriously and prepared myself with some proper training. In this post I'll have a look at the trend data from my WHOOP in preparation for the Elfstedentocht.

Wearing WHOOP 4.0

Why you should wear a biometric sensor

Jan. 14, 2022
Use WHOOP to see the impact your choices have on your body, think of it as a special kind of mirror - it's so powerful, that I don't take mine off!

How often do you look in the mirror? Probably more than a few times a week! I have been thinking about this ever since I received my newest WHOOP 4.0 biometric sensor. It's great. But, why do I wear it? What value does it provide? Why should you wear it?

The birth of a child

Impact on daddy and his biometrics

July 13, 2021
Witnessing the birth of a child changes a man, for science and curiosity I wore a biometric sensor capturing the impact of birth on yours truly.

Today I witnessed the birth of my daughter! You feel humble as a man, witnessing the labour and magic. Not sure if I can come up with something having more impact on a man than this. For the purposes of science and curiosity I wore a biometric sensor, and this is what it recorded.

Enter text without keys

Tap: the wearable keyboard and mouse

Apr. 15, 2021
 Worn on your fingers, the Tap Strap recognises tapping and moving to control and type without a mouse or keyboard!

This month a special piece of wearable tech arrived for me to try: the Tap Strap. Worn on your fingers, the Tap Strap recognises tapping and moving. It enables you to control and type your computer without a mouse or keyboard!

Riding with Omata One

Analogue cycling computer with GPS

Sep. 29, 2020
If you're looking for an alternative for common cycling computers, the Omata One is something truely special: it indicates your speed, distance, ascent and time ridden using mechanical hands!

For the past week I have been riding my bicycle with Omata One, a special bike computer. Its mechanical hands indicate speed, distance, ascent and time ridden measured using precise GPS data. It is fun, read along to know why.

Improve your sleep by blocking light

On the benefits of wearing a sleep mask in bed

Jan. 24, 2020
I have been wearing a sleep mask in bed, blocking all light. It has been amazing for my sleep's quality. Read along for my findings!

Over the past few weeks I have been experimenting with wearing a sleep mask in bed, blocking all light. Our bodies produce the sleep hormone, melatonin, in darkness. Living in an environment awash in artificial light, is therefore exactly the sort of thing that disrupts one's circadian rhythm. Can a simple mask help?

Whoop strap review: 24/7 wearable sensor

Beyond fitness tracking and smartwatches

Dec. 31, 2019

The past months I have been wearing the WHOOP Strap 3.0, a wearable sensor that collects health and fitness data. It's different compared to most other fitness bands as it was designed with professional athletes in mind. It is focussed on daily strain, recovery and sleep. Read along to find out how this works.

Realtime human pose recognition through computer vision

Using TensorFlow and PoseNet on a video feed

Dec. 1, 2019
For an exciting new project I have been experimenting with TensorFlow, enabling realtime pose detection using PoseNet.

For an exciting new project I have been experimenting with computer vision using TensorFlow. I wanted to achieve realtime human pose detection to drive interactive video projections and games. Time to dive into the world of machine learning, tensors and computer vision!

Riding with a power meter on your bike

Installing and using the 4iiii Precision Powermeter

Aug. 28, 2019
In this post I describe my experience with installing the 4iiii Precision Powermeter on my road bike.

After I created a minimal road bike, I decided to install a power meter to find out what's it like to measure the power output of my legs. What can you learn from a power meter? Is it difficult to install? Is it worth it? Read along to find out.

Limitations of sleep tracking using a wearable

Comparison with a chest strap HR-monitor

July 16, 2019
Limitations of heart rate analyses during sleep, why you should reconsider tracking your sleep.

Sleep monitoring is a popular feature of many smartwatches and wearables. Devices like Fitbit, Withings, Apple Watch and Biostrap analyse biometrics during your sleep. These wearables are worn on the wrist and use optical sensors to capture your heart rate. I wondered how the optical sensors would compare to a high resolution chest strap HR-monitor.

Optical vs chest strap heart rate monitors

Measuring beats per minute using different sensors

July 15, 2019
Understanding the differences in common HR monitors used in wearables, smartwatches and fitness trackers

With modern wearables, smartwatches and fitness bands, it has become easy and common to measure your heart rate. There are however fundamental differences in sensor types. Some sensors capture the electrical signal from your heart while others use light to analyse the blood flowing through your vessels. If you're interested in measuring heart rate, it's good to understand these differences.

Solo around the Markermeer (211KM)

Tips to prepare, to endure and to enjoy long distance cycling

May 29, 2019
This week I took my bike for a long distance (211)KM ride around the Dutch Markermeer, solo! Read along for practical tips for long distance cycling.

This week I took my bike for a long distance (211KM) ride around the Dutch Markermeer, solo! Unlike participating in an organised event with service, support and company along the way, going solo requires a different preparation, mindset and planning. Read along for some practical tips for long distance cycling.

The best bike computer app: Cyclemeter

Get advanced ride data with a flexible setup

Apr. 30, 2019
Collect advanced bike ride data using your smartphone connected to external Bluetooth sensors and a steer mounted display.

This month I have intensified my training to become fit for this year's Fietselfstedentocht, a 235KM bicycle ride through Friesland. Over the years I have tested different kinds of bike computer setups: from dedicated (and expensive) Garmin Edge bike computers to no data at all. Eventually I came up with a flexible setup to gather advanced ride data using my smartphone, let me explain how this works.

Swimming and cycling with Apple Watch

Different activities in the workout app in watchOS

Sep. 27, 2018
This month I tested the newest watchOS while swimming and cycling.

This month Apple launched a new Apple Watch series and released an update to watchOS. The focus of the smartwatch is more and more gearing towards health and fitness. This made me curious, how well does Apple Watch work for different activities?

Listen to your body

Why I stopped using health and fitness sensors

May 17, 2018
Using health data gathered by sensors and wearables I learned to listen to my body. Now I have stopped using bluetooth sensors all together.

A good customer of mine was once a physiotherapist, he told me about people asking him to "feel their muscles" to tell them how they where doing. "Crazy!" he told me: "I can never feel better than the people themselves, if they only would listen to their body". This caused me to question the health and fitness sensors I use.

Outside the comfort zone: amateur acting

Wearing an heart rate monitor during my debut performance

Apr. 18, 2018
This month I strapped myself with sensors during a little experiment outside my comfort zone: I debuted as amateur actor!

This month I made my debut as amateur actor. I am no Hollywood star, nor do I envy to become one. But I do like crazy experiments and operating outside of my comfort zone often leads to new and refreshing insights. I took part in an amateur drama play and - in the name of science and fun - strapped myself with sensors to measure what happened to my body.

Commuting by bike

One week (240KM) on the VanMoof Electrified S

Dec. 2, 2017
One week on the VanMoof Electrified S E-bike testing it for commuting and comparing it to a normal bike.

For a few years now, I commute to work using a bicycle. I have lost more than 15KG since I stopped using my scooter. This week I tested a VanMoof Electrified S, an electric bike with an industrial, minimal design. Is it any good? How does it compare to a normal bike? Will an electric bike make you lazy? Read along to find out!

Collecting health data with Biostrap

Wearing a clinical-grade photoplethysmography (PPG) sensor for a month

Nov. 15, 2017
Wearing a clinical-grade PPG sensor for a month to collect advanced biometrics from my wrist.

Most wearables (smartwatches, fitness trackers, etc.) use very basic sensors to capture heart rate. Their signal is binary: just counting beats. Biostrap is different, instead of just checking pulses, it captures a high-fidelity PPG waveform. These waveforms are the same kind that doctors use, making me wonder what I could learn from them!

Fietselfstedentocht 2017

Cycling the 235KM bicycle tour through Friesland

June 30, 2017
Cycling the 235KM long Fietselfstedentocht through Friesland

This month I cycled the Fietselfstedentocht, a 235KM tour through Friesland. This tour brings you through various Frisian cities throughout one of the most Northern provinces of the Netherlands. The tour was first organised in 1912 and has grown to become legendary due to its history, challenge and popularity; well worthy of a blog post!

One year of cycling

GPS recording an entire year of bike rides using Garmin and Strava

Dec. 31, 2016
GPS recording an entire year of bike rides using Garmin and Strava.

One year ago I started recording all my bike rides, including commutes, short grocery trips and long Gran Fondos. I equipped my bicycles with Garmin Edge computers that recorded location (GPS), speed, cadence and my heart rate. I covered more than 7683 kilometers during 320 hours of riding. It's time to review all the data and share some photos I took along the ride!

All blog posts
Not your average debugging session: Fietselfstedentocht 2024
Not your average debugging session: Fietselfstedentocht 2024
Flyer announcing the play
Flyer announcing the play "Zusters in Zaken" by "De Opregte Amateur"
The outer ring is easy to operate with gloves on, it is precisely engineered from 6063 aluminium and has a nice tactile feel to it
The outer ring is easy to operate with gloves on, it is precisely engineered from 6063 aluminium and has a nice tactile feel to it
Apple Watch uses an optical sensor to perform its automated heart rate monitoring
Apple Watch uses an optical sensor to perform its automated heart rate monitoring
Front light is integrated into the frame
Front light is integrated into the frame
In addition to commutes and grand fondos I also recorded short trips to the grocery store. Like this one on the
In addition to commutes and grand fondos I also recorded short trips to the grocery store. Like this one on the "Beer Bike".
WHOOP 4.0 is smaller than its predecessor - packs more sensor technology - allows for easy charging while wearing it
WHOOP 4.0 is smaller than its predecessor - packs more sensor technology - allows for easy charging while wearing it
Something is missing... my front wheel!
Something is missing... my front wheel!
4iiii Precision Powermeter - used by the professional cycling team Quick-Step / Bora Hansgrohe
4iiii Precision Powermeter - used by the professional cycling team Quick-Step / Bora Hansgrohe
Apple Watch workout app shows large buttons to start a workout - no need for additional configuration
Apple Watch workout app shows large buttons to start a workout - no need for additional configuration
My HRV measurements going down... as result from lack of training during my family's move from the city to country side
My HRV measurements going down... as result from lack of training during my family's move from the city to country side
I have gained weight as I lost fitness: confirming that WHOOP is on to something: there seems to be an inverse correlation between my weight and HRV trends
I have gained weight as I lost fitness: confirming that WHOOP is on to something: there seems to be an inverse correlation between my weight and HRV trends
Worn on the bicep, WHOOP easily hides under your clothing - indicated with blue arrows - keeping your wrists free for mechanical watches
Worn on the bicep, WHOOP easily hides under your clothing - indicated with blue arrows - keeping your wrists free for mechanical watches
Yours truly dressed up and ready - it's an incredible privilege to be able to witness the surgery as a man - big, big thanks to the hospital staff!!
Yours truly dressed up and ready - it's an incredible privilege to be able to witness the surgery as a man - big, big thanks to the hospital staff!!
First gran fondo was cycling around the Dutch
First gran fondo was cycling around the Dutch "Markermeer", a 208.5KM ride.
Bike in the local bike shop
Bike in the local bike shop "werkplaats" (Dutch for workshop)
Riding my bike as workout (photo by Niels)
Riding my bike as workout (photo by Niels)
How the Tap Strap works
How the Tap Strap works

More Sensors on Willem's Blog

All blog posts

Articles (151)