Tiny Particle Sensor Node with Decorative Case

This article is about a small sensor node with a decorative case. It is based on the Raspberry Pi Zero W board with a custom sensor shield on top.

I publish all hardware files for a simple version of the sensor, so you should be able to build this kind of sensor nodes and use it to monitor anything you like. You can also extend/modify the design easily with additional sensors. Nevertheless, the case lid design is based around the Plantower PMSA003 particle sensor. It has all required air vents for this use.

The term “node” is used, because the idea of this sensor is to use a large number of these nodes in a network to monitor location and time based sensor data.

I cannot publish any software at this point, until I have a simplified and redacted version which I can publish under an open source license. Yet, accessing the sensors of this node is dead simple and can be easily done.

The Required Hardware

The simplified design is assemble using the following components:

The Raspberry Pi Zero W

I use the Raspberry Pi Zero W because of the very compact size and computing power. Each node can prepare the sensor data, which takes a lot of load from the central processing unit. Also, using a platform like the Raspberry Pi easily allows to run a whole web server on each node – so one can query the sensor data of each node independently. This makes testing a breeze.

Continue reading Tiny Particle Sensor Node with Decorative Case
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How to Automate the Turn-On Time of a Deco Light

I own a decorative light for the winter which I controlled using a simple time switch in the past. The time of dusk is continually shifting, so I had to adjust the turn-on time multiple times each year.

This year, I planned to automate the turn-on time. I tried to find a light controlled switch, which automatically enables the decoration on dusk and disable it on dawn. I saw no suitable one.

I ended adding an own switching circuit to the decoration. This article describes how to build an own controller as I did and highlights a few problems you may encounter.

The Issues with Off-the-Shelf Solutions

My requirements for the off-the-shelf solutions were:

  • Setting to adjust the light level.
  • Suppression/identify the light from the decoration.
  • Turn off at a given time or dawn.
  • It shall work at a temperature of -10ºC.

Sadly, I found no simple device, which matched all my requirements. I also noticed, most of these devices had horrible ratings and reviews – mainly because they lacked the described features.

Adjusting the light level seems a straight forward requirement. The brightness, where you like to turn the decoration on is a matter of personal taste. Most devices I found do not let you adjust this.

If the decoration is turned on, it will naturally get brighter outside. If the switch does not compensate for this fact, the light will start to blink. In this case, you had to place the sensor somewhere carefully it is not affected by the light of the decoration.

Most devices just let you select a duration, how long the light stays on. This is the cheapest way to implement a device like this. It makes not much sense though. Because the time of the dusk is moving, the time when the light turns off shifts as well. Useful is either turning the light off at dawn, or at a fixed time.

Then, there I found one device which had all the previous features, but it was rated to indoor use only. The minimum working temperature was 5ºC.

Initial Situation

The initial situation is shown in the following illustration:

A timer connects to the mains plug. The mains adapter of the decoration connects to this timer and converts the 240V AC power to 24V AC. This AC voltage is somehow a standard way to power old, filament lamp based decorations.

Continue reading How to Automate the Turn-On Time of a Deco Light

Snow Flake Project Documentation

I wrote a short page about the snow flake project from end of 2017. On the page you will find a summary of the project and the link to the repository with all the required files.

Everything is open source, including the design files for the hardware and a base version of the firmware for the project.

You need some experience if you plan to produce your own snow flake boards, but this is a beautiful and very rewarding decoration. 

Click on the following link to visit the project page:

Snow Flake Decoration

If you have questions, miss some information or just have any feedback, feel free to add a comment below.

Have fun!

Good Quality Boards from PCBWay

Recently I received boards for a sensor array from PCBWay. This boards were made in a very good quality considering the low price level.

I really like the green solder mask they use, it creates a nice optical effect shifting the green colour towards yellow somehow. The solder mask produces a very nice contrast between the copper and non-copper areas, easy to see all traces.

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The small traces on this board have a width of 0.2mm with an insulation of 0.3mm. It is a lead free HAL which is nice and flat.

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Production time was two days (over the weekend) and shipping using DHL took four days.

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Routing of the boards is nice and smooth, there are no traces of tabs left on the boards.

All boards will be connected with a kind of bus in a circle arrangement as shown in the title image and the image below. There is an address selector on each board, to assign each sensor board an unique address.

By splitting the design of the sensor array into five equal boards, I could save a huge amount of production costs. Producing 10 of the shown boards, lead free HAL, with a production time of 2-3 days was just $19.

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If you have questions, miss some information or just have any feedback, feel free to add a comment below.

Have fun!

How to Deal with Badly Written Code

Sadly there is a ton of badly written code out in the wild. Hardware related code, seem to suffer more in this regards. I imagine, many developer in this segment are unwillingly to invest time in quality or are just inexperienced.

Even if you are dedicated in reliable and high quality code, you will probably run into the situation, where you have to use a library with really low standards.

Strategies

There are a number of strategies to deal with this code:

  1. Rewrite the library.
  2. Refactor the code.
  3. Wrap the library.
  4. Wrap the interface.

Rewrite the Library

This is actually the best you can do and it is also the most time-consuming approach. Yet, write the code from scratch will give you several benefits:

  • You will perfectly understand how the original library and the accessed hardware works. Actually you have to understand it, otherwise you are unable to rewrite the code.
  • The new code will be modern, fast, reliable and in your coding style.
  • If you open source the new code, you will give people an alternative and a better example how to implement something the right way.
  • You can also selectively remove unwanted/bloated parts from the original code, which can reduce the overall binary size of the final project.
  • It will also give you the option to implement a proper error handling in the new code.

If you have the time and motivation to rewrite the code, do it!

Refactor the Code

Changing the code, without changing the functionality is called code refactoring. This is a good strategy, a compromise, between rewriting and wrapping. Usually you will just go, line by line, through the original code, modernise it and cleaning it up.

Continue reading How to Deal with Badly Written Code

Make your Code Safe and Readable with Flags

Flags play an important role in embedded software development. Microcontrollers and chips are using registers where single bits or combinations of bits play a big role in the configuration. All the bits and their role are described in the specification, but writing the bits directly in the code would be very confusing and hard to read:

AHBMASK.reg = 0x14 // Huh!?

For this reason it makes sense to write an interface to access the registers of a chip. This interface will define identifiers, in the form of constant values, to build bit combinations to write into the registers.

The Outdated and Bad Approach

Chip manufacturers are well known for their extremely bad and outdated interfaces to access chip registers. Let us have a look at the CMSIS implementation from Atmel. This is part of the interface to access registers in one of the microcontrollers. Please ignore the copyright block, it is just added for legal reasons.

To be fair, CMSIS is a hardware abstraction layer standard defined by ARM. It shall standardise the software interfaces across all Cortex-M products. Therefore Atmel had no choice as to follow this standard.

Do you feel the dust on this code? There are a vast amount of problems caused by this interface.

First the values are defined as macros instead of constants. All this identifiers will clutter the global namespace of your code and make naming conflicts very likely. Way better would be using simple constants like this:

const uint8_t PM_AHBMASK_DSU_Pos = 3;
const uint32_t PM_AHBMASK_DSU = (0x1ul << PM_AHBMASK_DSU_Pos);

This would give the compiler the correct hint about the used data type for the registers. All this constants could be put into a own namespace to prevent any name collisions with the user code.  It would still not prevent incorrect assignments.

I can write and compile the following code, which absolutely makes no sense:

CPUSEL.reg = PM_AHBMASK_DSU; // nonsense!

There will be not even a compiler warning about any problems and this is exactly what makes debugging embedded code very difficult.

Use the C++ Language!

I personally think, many software developers writing C++ code for hardware do not make fully use of the language. One reason could be the lack of support of many language features at the beginning or just the lack of experience.

In the the last 10 years, there was a huge progress in the development of the C++ language. Ignoring this progress would be silly in my opinion. Especially the C++11 standard added lots of useful features to the language.

A good support for the C++11, C++14 or even better for C++17 is very important, especially for embedded software development. Many of the introduced features will improve your code, make it simpler and more readable, without adding any additional byte to your firmware.

The features I describe in this article will not increase the size of the final firmware, they will just affect safety, readability and simplicity of your code. At the end, the optimiser in the compiler will resolve all the code and generate small and compact binaries.

Continue reading Make your Code Safe and Readable with Flags

Testing the TPS61092 Boost Converter

For my current project I searched for a good boost power converter which is able to deliver continuous 400mA power for various sensors.

There are an endless number of good boost converters around, but not many can be hand soldered to a board. I would really like to see some like the TPS61092 with SOIC or similar packages. The biggest problem seems to be the heat transport, why most chips have to be mounted flat on the board.

Before using the chip in my project, I created a small test board. Using this board I can test various things. First I liked to test the performance under load. Next I tested if the chip can be hand soldered and finally I tested the final board layout I will use in my project.

Performance

The performance of this chip is really good, producing a very stable output. I designed everything for a load up to 2A with all suggested components from the specification. There will never be a higher load than 0.5A, so I probably could use a smaller coil for the final project.

thermal image

Running under 0.5A load from 3.3V for over half an hour, the chip stays quite cold. Even in my case, where the chip bottom is not directly soldered to the board, it seems to be able to transfer the heat into the board. This is nicely visible in the thermal image of the board.

The Board

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The board was produced by OSH Park in a good quality. If you like to experiment with this chip, you can order this board very cheap at OSH Park using the following link.

Continue reading Testing the TPS61092 Boost Converter

PCBite Kit 2.0 from Sensepeek Arrived

Last week the new PCBite Kit 2.0 from Sensepeek arrived. The new kit comes with the great PCBite holder from the previous version, which are very useful to fasten a PCB for soldering, rework or analysis. New to this kit are the handy probes, which also can be magnetically attached to the mirror board.

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The mirror finish of the board let you keep the bottom side of the board in sight while you are working on the top side. It is a very useful feature, like in the example shown in my photos where I analyse the communication of the snow flake board and can see the LEDs on the bottom side.

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The probes have a nice weight and come with a very precise gold needle tip. You can easily place them on even the finest pin or trace. The tip contains a spring like a pogo pin, therefore it keeps an equal amount of pressure on the board and does not move if there are vibrations or if you carefully move the board around.

With each probe, there is also a different needle with a crown tip. This alternative tip is more like a really tiny fork to be placed on small wires and pins. Continue reading PCBite Kit 2.0 from Sensepeek Arrived

Open Position for Step-Up Converter

For a current project I need a step-up converter to get 5 volts from 2.5V-5.5V input. The output of this converter is used to power sensors which drive motors and small heat elements from this source. The average consumed current is 160mA with a peek at 320mA.

In the photo you can see the latest Boldport project with a test setup for the XC9142B50DMR-G from Torex Semiconductor. I made the mistake and just relied on the specifications stated on the website from Mouser:

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This looks really good: 500mA output current… So I did a quick test. Obviously the magic smoke in the photo is a composition, but this is what actually happened somewhere at a constant ~250mA load with 5V input. Continue reading Open Position for Step-Up Converter

Adafruit PCB Coaster Arrived

Today I got the PCB coaster from Adafruit. They look so much better in real than on the photos in the shop. The coasters are made from 2.4mm FR4 PCB material. There is a transparent solder mask on the top to protect the copper and gold elements. The frame around the image is black silkscreen.

I really like the combination of the cold and coper colours.

The coasters were designed by Saar Drimer at Boldport. You can buy them in the Adafruit shop.

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