Difference between revisions of "User:Bertrik Sikken"

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This is a list of ideas I'm thinking about, but have not fully developed into an actual project yet.
This is a list of ideas I'm thinking about, but have not fully developed into an actual project yet.
=== Interact with Umeter ===
Umeter.nl can request electricity usage data from an energy provider.
This project is about interacting with their backend.
Source code: https://github.com/bertrik/umeter-api
=== Visualisation of dutch day-ahead energy price ===
=== Visualisation of dutch day-ahead energy price ===

Latest revision as of 13:45, 29 September 2022

User info Bertrik Sikken
Name Bertrik Sikken
Nick bertrik
Tagline heb ik niet

You can reach me at bertrik@sikken.nl or bertrik@gmail.com.

Studied Electrical Engineering at Twente University.

Main interests:

  • reverse-engineering things (USB stuff, mp3 players), working on http://rockbox.org
  • studying bats and making electronics for recording/listening to bat sounds
  • radio stuff, in particular software-defined radio

Projects I work(ed) on (refresh):

 Project Status
Pico TrackersAbandoned
Secure iButtonCompleted
AntiLostIn progress
AudioMothIn progress
CubeCellIn progress
EspAudioSensorIn progress
Esp32camIn progress
FMCWRadarIn progress
LoRa-E5-miniIn progress
LoraWanDustSensorIn progress
Msi2500SDRIn progress
Sim7020In progress
StereoBatRecorderIn progress
UltrasonicPlayerIn progress
... further results

Project ideas


This is a list of ideas I'm thinking about, but have not fully developed into an actual project yet.

Interact with Umeter

Umeter.nl can request electricity usage data from an energy provider. This project is about interacting with their backend.

Source code: https://github.com/bertrik/umeter-api

Visualisation of dutch day-ahead energy price

A simple display showing the electrical energy price applicable to the current moment, from yesterday's day-ahead price from https://transparency.entsoe.eu/transmission-domain/r2/dayAheadPrices/show?name=&defaultValue=false&viewType=GRAPH&areaType=BZN&atch=false&dateTime.dateTime=28.07.2022+00:00%7CCET%7CDAY&biddingZone.values=CTY%7C10YNL----------L!BZN%7C10YNL----------L&resolution.values=PT15M&resolution.values=PT30M&resolution.values=PT60M&dateTime.timezone=CET_CEST&dateTime.timezone_input=CET+(UTC+1)+/+CEST+(UTC+2) (for example)

Consists of a REST service that fetches the day-ahead prices and serves the price appropriate to the current time as a JSON message. Also calculates the *median* of energy prices over 24 hour period, so the light can indicate if the current price is 'low' or 'high' (hourly price > median price).

The light consists of an ESP8266 controlling a 4-digit 7-segment display.

Automated bat counting

Can we automatically count the number of bats from the image of a webcam mounted in a bat colony? Perhaps using some kind of AI or machine learning algorithm?

The image in question: https://stofradar.nl/coenecoop/


I received a kind of XBEE zigbee router/repeater. Info

Use TheThingsIndoorGateway as Helium hotspot

I have a spare TTIG that could perhaps be used as a Helium gateway, investigate what is possible.

One possiblity is to capture the gateway traffic from the TTN gateway events API, convert uplink data to a format that the Helium network understands and forward it. I don't really care about the Helium crypto tokens, this is just for fun and science.

What I definitely can do:

  • Capture data from the TTN gateway events API, convert it back to Semtech UP format and forward it somewhere to Helium (just not sure where!)
  • See also my https://github.com/bertrik/ttn-gateway-collector project which contains an initial implementation of TTN-to-UDP conversion


  • If you want to be a gateway on the Helium network, you have to *pay Helium*! Obviously I don't want that, I just want to share data to improve *their* network.

Open work:

  • investigate if Helium has an open uplink API for their hotspots, if so study it etc, without paying the gateway fee

Interesting stuff:

Adding BLE GATT interface to sensors

The GATT specification allows measurement properties to be defined and transferred continuously over Bluetooth low-energy.

With GATT you can define a collection of properties (e.g. measurement items like temperature/humidity/particulate matter/noise, etc) organised in a simple structure of a BLE service. The 'notification' method allows you to basically push the data continuously to a connected host, e.g. a smart phone.

Services collects characteristic, a characteristic has values with units. Each of these (service, characteristic, unit) have their own unique "UUID". This is described in the so-called 16-bit UUID numbers document

Interesting stuff in GATT:

  • See GATT_Specification_Supplement_v5 paragraph 3.151, it has a noise characteristic with 1 dB resolution.
  • 0x27C3 is the GATT *unit* for sound pressure
  • 0x181A is the GATT environmental sensing *service*, document name "ESP_V1.0.0.pdf"
  • 0x2A6E is the GATT Characteristic and Object Type for temperature
  • 0x2A6F is the GATT Characteristic and Object Type for humidity
  • 0x2BD5 is the GATT Characteristic and Object Type for Particulate Matter - PM1 Concentration
  • 0x2BD6 is the GATT Characteristic and Object Type for Particulate Matter - PM2.5 Concentration
  • 0x2BD7 is the GATT Characteristic and Object Type for Particulate Matter - PM10 Concentration
  • Unfortunately I cannot find a characteristic for carbon-dioxide (CO2) in the BLE GATT unit document

See also https://programmaticponderings.com/2020/08/04/getting-started-with-bluetooth-low-energy-ble-and-generic-attribute-profile-gatt-specification-for-iot/

Reverse engineering XS-8217 bluetooth air quality meter

This is a thing that measures CO2, humidity, temperature, TVOC and formaldehyde.

See also https://wiki.liutyi.info/display/CO2/ZN-2CO3+Inside

This teardown looks a lot like my sensor: https://www.youtube.com/watch?v=APnjhMrJChI Mine contains a "TPM-300A" sensor for measuring VOC.

It has a bluetooth interface, device name is XS-8217. It has a BLE GATT profile, with the following services

  • service 0xC760
    • characteristic 0xC762 (WRITE)
    • characteristic 0xC761 (NOTIFY)
      • example data: 0x23 0x06 0x10 0x04 0xF1 0x00 0x23 0x65
      • example data: 0x23 0x08 0x10 0x04 0x01 0x9A 0x00 0x0A 0x00 0x03 0x0E
      • data shown on screen was approximately: CO2=418ppm, HCHO=0.003mg/m3, TVOC=0.013mg/m3, temp=24degC, humi=35%

So data in the characteristic 0xC761 seems to have a 4 byte constant header:

  • 0x23
  • length byte

Then we have for the first message: 0x10 0x04 0xF1 0x00 0x23 0x65

  • 0x10 0x04 fixed header
  • 0xF1 is temperature in 0.1 degree Celcius most likely (24.1)
  • 0x00 is ...
  • 0x23 is humidity most likely (35)
  • 0x65 is ... checksum perhaps

And for the second message: 0x10 0x04 0x01 0x9A 0x00 0x0A 0x00 0x03 0x0E

  • 0x10 0x04 fixed header
  • 0x01 0x9A is the CO2 concentration (410)
  • 0x00 0x0A is TVOC most likely (10)
  • 0x00 0x03 is HCHO most likely (3)
  • 0x0E is ... checksum perhaps

ribbon tweeter for bat audio

Someone gave me this idea: Use a ribbon tweeter like this for playing back bat audio: https://nl.aliexpress.com/item/4000973201791.html

The frequency spectrum shows no sign of dropping off at 20 kHz.

3d glasses

I got some 2nd hand 3d glasses, they look exactly like these ones:

The common name appears to be "G15-DLP".

A tear-down here:

Interesting documents:

Someone claims he got something to work with some hacks: https://www.avsforum.com/threads/how-i-got-cheap-dlp-link-glasses-to-work-great.1887145/


Op verschillende plekken in Gouda staat er water in de kruipruimte van huizen van bewoners. Kunnen we dat meten en inzichtelijk maken, voor bewoners, op een kaart bijvoorbeeld?


  • in de kruipruimte plaats je een module die waterhoogte kan meten
  • de module bestaat uit een microcontroller en een afstandsmeter, die de waterhoogte bepaalt
  • de gegevens worden via WiFi doorgestuurd naar een centraal punt, waar de data wordt verwerkt en gevisualiseerd
  • op een webpagina kan je een overzicht zien van alle meters die online zijn
  • de meting wordt gedaan door bijv. een laser-afstandsmeter of een ultrasoon-afstandsmeter
  • voeding? lastig, hoe krijg je 5v naar een potentieel natte plek?
  • kosten? verwachting < E 40,-

In Gouda wordt op veel verschillende plekken de grondwaterstand gemeten, zie https://opendata.munisense.net/portal/wareco-water2/group/581/Gouda-KJ38A , maar:

  • geen visualisatie op de kaart, je ziet alleen de meetlokaties d.m.v. een icoontje!
  • geen meetpunten in Gouda noord!

Online bat detector

Idea: use an ultrasonic microphone, connect it to a WebSDR, so people can tune into bat sounds remotely.

Blood pressure meter hacking

Apparently some blood pressure monitors can be hacked.

My goal is to be able to extract the list of the last 100 measurements somehow, so you don't have to type them over manually. Either using bluetooth (serial), or by adding something like an ESP8266 to sniff internally an make it available over WiFi.

Raspberry pi airplane tracking

Apparently now you can also participate in MLAT tracking of planes that don't transmit GPS coordinates themselves.

APRS gateway



Small inexpensive modules that play mp3 from an internal flash. Could be nice for a custom door bell for example.

More info at:


Cheap FPGA boards and nice applications:

Neural networks on low-end hardware

Investigate if you can run a powerful neural network on relatively low-end/cheap/low-power hardware. For example a Raspberry pi. A RPI runs Linux, run python, just like some common neural frameworks. Do we need hardware acceleration from the GPU and does the RPI GPU support that?

Read list:

Bought a MaixPy:

mini word clock in dutch

Basically an monochrome 8x8 word clock, in Dutch, showing local time in the Netherlands.

This git repo has the current code.

See here for a demo running on an arduino nano.

The plan is to run this from an ESP8266 instead of an arduino nano, so it can get the time from the internet using NTP. Andreas Spiess demonstrated on youtube how existing libraries on the ESP8266 can be used to do the local time (including summer-time) calculations.

Cypress PSOC5

Play with the Cypress PSOC5 platform, which combines a ARM Cortex-m3 processor with configurable analog blocks. I'm thinking of combining it with a 24 GHz doppler radar sensor, to process the signal and present it as a USB audio device (stereo signal contains I and Q parts). See RadarOnAStick.

Simple Doppler motion sensors

You can find basic doppler microwave motion sensors based on a single transistor, with some weird traces on the PCB very cheaply, for example

Typically the microwave part of these consists of a single transistor with a rectangular area on one leg and a meandering trace (with lots of vias to the other side) on the other leg. The output of this circuit seems to go into a chip very much like the ones used in PIR sensors.

See also https://github.com/jdesbonnet/RCWL-0516 for a reverse engineering effort of these doppler radar modules.

Bare-bones Arduino bat detector

This is an idea for a very basic heterodyne bat detector, doing signal processing on an Arduino, requiring minimal external components.

The basic principle of a heterodyne detector is that it just mixes (multiplies) the audio signal with a square wave, low-pass filters the result and puts it on a speaker.

Multiplying with a square wave can also be considered to be just alternatively inverting and not-inverting the signal. So if you sample an ultrasonic signal at twice the rate you want to multiply, you can just subtract odd samples from even samples and low-pass filter that.

How this can be done in an AVR Arduino:

  • sample the audio signal at twice the detection frequency, say 84 kHz. An AVR should just be able to do that.
  • apply a 1-pole IIR high-pass filter to remove DC bias, this takes one shift instruction and one addition.
  • multiply by the detection frequency, this means just inverting the odd samples.
  • low-pass filter the signal, this can be done using a moving average filter, say 16 samples long (first null at 5.25 kHz). Theoretically, averaging 16 samples should result in two bits extra accuracy. This operation takes some storage, an addition and a subtraction.
  • output the filtered signal using PWM, possibly at the same rate that we are sampling the input audio.

The microphone can be a 40 kHz piezo transducer, to keep it cheap (but also limited to 40 kHz). The pre-amplifier can be a single transistor with some resistors around it, providing about 40x gain. The arduino does the signal processing (mixing, low-pass filter) to shift the bat audio to human range. The speaker amplifier can just be a simple two transistor push-pull circuit, since the output from the Arduino is digital/PWM.

AVR Arduino sample rate

As far as I understand, the ADC clock can be set to 1 MHz. Conversion takes 13 cycles, so this can be a problem to reach a sample rate above 80 kHz.

GPS repeater

This idea is about experimenting with a cheap GPS repeater built out of an "active" GPS antenna.

The problem this solves is that often indoors you have no GPS reception, but you like to have some signal to experiment with (e.g. a LoRa tracker).


  • get a cheap active GPS antenna from AliExpress (some as cheap as E2,- !), most just mention one frequency (1575.42 MHz)
  • get a bias-T circuit to feed it the supply voltage (e.g. from a KOPPLA) and pass the RF signal onto an indoor antenna
  • the indoor antenna may be as simple as a 1/4 wave coax dipole: center conductor sticking up (about 47 mm), coax shielding is divided into 3 of 4 ground radials sticking sideways
  • build it and test it with a smart phone, tracker hardware, etc.

See also:

Indoor radar speed sign

This idea about placing a simple IQ-output radar sensor indoors in the hacker space, do some basic signal processing on the IQ doppler signal and determine movement speed and direction, then display this on a LED display. This is of no immediate practical use other than fun, but helps me to gain a bit more experience with microwave radar sensors and eventually build a more effective setup for detecting/counting bats flying in and out of a roost.

Implement this on a PSOC5 platform or on the STM32 using Arduino.