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Turbidity Visualization – alternative design

In the first turbidity node design I re-used leftover plastic of one of the bottle designs as the circuit carrier and copper tape for connections. This proved to be tricky as the heat during soldering would distort the plastic and dissolve the glue of the copper tape, making it lift off the surface and weaken the connections.

In a new attempt to provide a seamful design, this new prototype uses copper coated welding rods and copper wire as conducting elements and at the same time as structural element. This means the circuit would not require a surface, such as paper or plastic, but would only consist of conducting copper elements. For a first test I used a 1.2mm rod and experimented with soldering various wires and components to the rod. Soldering wire to the copper rod works well after removing the oxidation layer with sandpaper. The enameled copper wire also only solders well after sanding, which is time consuming when many components are involved. The advantage of this, however, is that the 3 dimensional circuit is less likely to be short-circuited, if parts accidentally touch – except for the conductive elements of the LEDs and the solder points.

I envisioned the test design to contain a set of 3 addressable LED sets that fit inside a glass jar. I bent the Ground wire into a circular shape to act as a base for the circuit which will connect to a set of LEDs to be controlled by a Wemos D1 board. After a hopeless attempt to use SMD LEDs for this circuit I found that 3mm LED diodes are much better suited for this kind of circuit.

In the end, I connected a set of three LEDs to three individually addressable wires. The copper rod needs to be bent carefully with flat pliers while the copper wire bends into shapes very easily. This gives the final circuit a quite messy look and I am unsure the design in this form would be suitable to provide any meaningful visualization of the turbidity reading.

The circuit appears quite fragile, the copper wires can be bent and crushed in the hand which gives it quite a unique aesthetic when handheld. Once transferred into a glass jar, the intricacies of the circuit design fade into the background, and the bright blue LEDs, as well as the battery and the small circuit board, distract from the fragile wires. I programmed the board with a simple test sketch that loops through the three LEDs.

The next step involves connecting this design to the turbidity sensor through my local MQTT network. I submerge my turbidity sensor into a glass bowl filled with water to get more realistic sensor data readings for this test. Unfortunately, the circuit design appears to be tricky to be programmed, and only after a while am I able to successfully de-tangle the wires that must have short-circuited somewhere, causing the code to malfunction and print nonsensical glyphs in the serial monitor when I try to debug my code.

Once my LED node is properly connecting to the WiFi network and correctly receiving the sensor data I map the turbidity to the amount of LEDs being switched on. To achieve a more murky fluid for this test I add a teabag to the water. I notice that the value changes are not as extreme as i would have hoped for and assume that a different resistor, perhaps a trimpot, would help to get more accurate data. Another issue with the sensor data is jumpiness. This could be because the LDR is just not suitable for an accurate measurement, or perhaps the sensor design is not waterproof and hence unreliable. Perhaps the code could be improved by measuring a running average over a couple of miliseconds, instead of measuring the brightness only once sand immediately transmitting this data.

Despite issues with the quality of sensor data, I learned a lot about the feasibility of this circuit design. While the copper wire gives the circuit a unique, messy look that I generally like, it is unsuitable for providing an easily understandable visualization of sensor data. Using only copper rods in combination with 3mm LEDs could work with a refined sketch on how to accurately map the sensor reading to an arrat of LEDs.

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Turbidity Output

For this turbidity LED prototype, I wanted to test if I could use a transparent material instead of paper. This would make the microcontroller and the battery more visible and provide more literal transparency in the design.

Planning an designing the circuit

To avoid more plastic usage I recycled an old bottle from the Moturoa installation for this prototype. As a first step, I removed the Moturoa stickers and cleaned it with methylated spirits.

During my initial research I looked for known scales or visual indicators for turbidity but mostly found visual gradients.

My first idea for visualisation was to link the brightness of an LED to the sensor value. For example, if the LED is at full brightness this means the water is clear; if it is of low brightness the visibility of the water is low. An issue with this approach is, that it might be difficult for a viewer to estimate the maximum brightness of a single LED. Hence, a viewer might not be able to extract meaning from the displayed value. LED brightness is generally a hard thing to estimate, especially in bright sunlight.

A solution could be to have a reference LED next to the indicator LED that is always at full brightness as a comparative value. The indicating LED could also be faded on first to a complete maximum brightness and then dimmed to the readout value read by the sensor. This could work, but this method might be too complex and create confusion on how to understand turbidity.

A simpler idea would involve visualising turbidity with an array of LEDs. If water clarity is at 100%, all LEDs are on. At 0% all LEDs are off, at 50% half of the LEDs are on (see sketch above). Using a variable brightness of the rightmost LED could work here to indicate a finer range of turbidity (25% would be one LED on maximum brightness and the neighboring LED at 50%). This idea is simple but does align with the design of previous prototypes. The Wemos D1 mini has nine digital pins in total. I chose to use six LEDs for this prototype because this allows seeing all LEDs from one angle while leaving enough space (around 15mm) in between the 5mm copper tape lines.

Assembly of the copper tape circuit

The plastic insert should fit inside a glass jar and it should be fitting into a variety of jar sizes. I place the six copper trails to the digital pins on the top of the plastic cylinder. I decided to line the bottom of the cylinder with one continuous piece of tape as ground (GND).

For this light probe, I chose blue SMD LEDs, mostly because I haven’t used this colour in any other probes so far. I apply some solder on the copper tapes first before placing the SMD on the circuit with a pair of tweezers. Then I melt one solder to tentatively put the LED in place before finalising the solder points on both sides. As anticipated, plastic and copper tape are not an ideal combination. Too much heat from the soldering iron melts the tape layer of the copper tape and lifts it off the surface (as with paper). The heat additionally shrinks the plastic and eventually deforms the entire surface.

Before adding another LED I test every solder connection immediately by connecting a 3V power supply. This involves checking whether the solder point is good enough and if the polarity of the LED is correct. This batch of LEDs was easier to place on the circuit as they feature a clear polarity mark on the top.

To finalise the circuit I decided to solder copper tape ends together instead of taping them. Using sellotape to bridge copper tape ends has turned out to be a weak connection point in previous prototypes. This turned out to be a problem especially once I needed to bend the paper circuit to fit into the jars. The soldered connections are more stable and reliable. Unfortunately, the additionally applied heat and solder gave the GND copper tape a somewhat messy look.

Connecting the circuit to the micro controller

After placing the finished circuit into a glass, aesthetic details of the copper tapes become less obvious. The bright blue LED becoming the visual focus of the prototype.

The final soldering job involved attaching wires to the circuit that could connect to the WeMos D1 mini microcontroller.
I chose a piece of CAT5 wire and first soldered seven strands (6 digital pins plus 1 GND) to a row of pin headers to be plugged into the microcontroller. Once completed, I soldered them one by one to the copper tape circuit.

The assembly of the electronic components of the prototype are completed now. The next step involves writing code to link the LED brightness to the readout of the turbidity sensor.

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A stream wellbeing LED jar: Water Temperature Visualization: Part I

My DIY water sensor nodes need field-compatible outputs so that visitors can easily access and understand the sensor data of the IoT network in real-time. The design for the temperature visualisation is based on the concept of the previous paper circuit for the EC probe, because research participants generally gave the design with cardboard, copper tape and white LEDs positive feedback. For the water temperature jar, however, I am using coloured LEDs, as suggested by one participant. In my development notes below, you can learn how I designed and assembled the device, and how the SHMAK manual (NIWA, 2008) helped to make the visual output meaningful. The idea for using cardboard and copper tape for these prototypes is inspired by the work by Jie Qi (2012) and the High-Low Tech Group at MIT Media Lab (2012). 

Development Notes

Similar to the previous LED prototype I use a 12cm high sheet of white card paper as a base for my copper tape trails. During an evaluation discussion on the EC jar design, participant 18 suggested the use of coloured LEDs for future iterations. I am attempting to implement this suggestion in the design for the jar that visualises the data coming from the water temperature sensor (DS18B20).

Evaluating the EC jar design with research participant in the lab (Jan 2019)

Visualising stream wellbeing

During the ideation phase, I focused on a suitable way to connect coloured lights meaningfully to the water temperature readouts. Hence, instead of opting for a traditional water temperature colour scale for blue (cold) and red (warm) I departed from the perspective of the stream, and what effect water temperature has on the more-than-human wellbeing of the stream.

Water temperature

Water temperature

Stream temperature is important because every species has a preferred temperature range. The range varies considerably from species to species. Sometimes, a temperature change is important, for example, as a trigger for egg hatching in some mayflies. Many organisms are unable to survive in temperatures above about 30 °C (except for some adapted to life in hot springs). At the other end of the scale, temperatures below freezing point constitute a very harsh environment because of the effects of ice.

A single temperature measurement is not particularly informative, but a series over time will provide a rough picture of the temperature regime in a stream. The longer the series and the closer together the measurements, the more informative the series will be.

Temperature depends largely on time of year and weather conditions. Stream type also plays a part. For example, lowland streams tend to experience quite stable temperatures (i.e., closely following average air temperatures). Shading along streams reduces the occurrence of extremely high water temperatures.

Water temperature fluctuates on a daily basis and for this reason it is suggested that measurements are always conducted at the same time of day.
Less than 5
Rating: fair
Score: 5

Less than 5°C

Values below 5 ºC are low and indicative of winter conditions in southern regions. Invertebrate and periphyton growth would be slow in such waters. Some species may be excluded.
5 to 9.9
Rating: good
Score: 8

5 to 9.9°C

Values of 5 to 10°C are moderate to low and indicative of winter conditions. Most invertebrates and periphyton can survive well in these temperatures.
10 to 14.9
Rating: excellent
Score: 10

10 to 14.9 °C

Values of 10 to 15°C are very suitable for most invertebrates and periphyton.
15 to 19.9
Rating: good
Score: 5

15 to 19.9°C

Temperatures of 15 to 20°C will start to be stressful for some invertebrates (e.g., stoneflies).
20 to 24.9
Rating: fair
Score: 5

20 to 24.9 °C

Temperatures of 20 to 25°C are moderately high. Some invertebrates, such as some mayflies, stoneflies, and some fish, such as trout, are unlikely to survive such conditions for prolonged periods (e.g., several weeks).
25 to 29.9
Rating: poor
Score: 0

25 to 29.9 °C

Temperatures between 25 and 30°C are likely to be stressful to fish, stoneflies, mayflies and some caddis flies. Such high temperatures may be a result of lack of shading and very sluggish flows.
30°C or more
Rating: poor
Score: -5

30 °C or more

Temperatures over 30°C are likely to be very stressful to most stream life and result in their death. Again, such high temperatures may be a result of lack of shading and very sluggish flows. However, stream temperatures will rarely get to these levels.

Table 1: Habitat indicators of stream health. From NIWA (National Institute of Water and Atmospheric Research), 2008.

The table contains seven water temperature bands rated from poor to good. I opt to use one LED for each band, representing the ratings (poor, fair, good, excellent) with colour. I choose red, yellow and green LEDs to indicate the stream health rating:

Red Poor
Yellow Fair
Green Good
Green x2 Excellent

Copper tape circuit design and assembly

To accelerate the development, I aim to build simple straight copper trails first as a proof of concept instead of spending time on developing a unique visual aesthetic for the circuit design without knowing whether the general concept works. I use the same circuit design as for the LED jar, but I need to recalculate the spacing for this version to fit eight rows of copper tape on the paper.

The Wemos D1 has seven digital outputs which makes it suitable for addressing seven LEDs individually. With the 8th digital output unused there is an opportunity for of adding a white LED on top later crossing all other outputs with sellotape, that could indicate the status of the network, similar to the EC jar.

The biggest challenge when making circuits with copper tape is the needs careful treatment and patience to make sure connections don’t break.

I use a craft knife to make precise cuts where the LEDs will be soldered in later.

I align the LEDs on the page so that the output can be seen best from one single perspective, that should later face towards an accessible area by the stream.

After all the LEDs are soldered into the circuit I test the quality of my solder points with a voltmeter.

Then I manually apply the forward voltage of each LED separately to test whether the connections work up until the edge of my circuit, where I will later add the connections to the microcontroller.

Challenges, reflections and learning outcomes

When working with SMD LEDs, I encountered the following issues:

  1. The LEDs are tiny and their polarity is barely visible from the top.  Sometimes LEDs move during soldering or don’t connect properly. I need to make sure I don’t accidentally move or flip them when working on the circuit touching the circuit with my hands or the tip of my soldering iron.
  2. The LEDs that I am using have a clear lens. I need to be careful to not mix up LEDs of different colours. The only way to know their colour is to power them on, which is tedious when dealing with the SMD form factor.
  3. Components close to each other don’t work well with copper tape. There need to be at least some centimetres of tape between two components.

In the sketch above you can see that my reference paper for the LEDs has moved in the process of adding LEDs which resulted in me picking the wrong LEDs for the first two rows. After removing the wrongly coloured LED I also realise that two green LEDs in series will not work for the “excellent” category as that would require a voltage of 2*2.2V which the microcontroller cannot supply. After making too many errors, I decided that I call it a day after testing that all the other LEDs work and will continue lab development after a healthy amount of sleep.

  

References

High-Low Tech Group, MIT Media Lab. (2012, August 21). Paper circuits. Retrieved February 27, 2019, from http://highlowtech.org/?p=2505
 
NIWA. (2008, December 17). Habitat indicators of stream health. Retrieved February 27, 2019, from https://www.niwa.co.nz/our-science/freshwater/tools/shmak/manual/9habitat
 
Qi, J. (2012). The Fine Art of Electronics: Paper-based Circuits for Creative Expression (Master of Science in Media Arts and Sciences). Massachusetts Institute of Technology, Massachusetts, NE. Retrieved from http://web.mit.edu/~jieqi/Public/Jie_Qi_MS_thesis.pdf
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Temperature visualization: Part II

The design for the temperature visualisation is based on the concept of the previous paper circuit for the EC probe but uses coloured LEDs that indicate the water temperature in relation to stream health, as listed in the SHMAK manual by NIWA (2008). The idea for using cardboard and copper tape for these prototypes is inspired by the work by Jie Qi (2012) and the High-Low Tech Group at MIT Media Lab (2012).

For finishing the circuit, I need to add resistors to the design as they have a smaller forward voltage than the white LEDs I used in the previous design. Using Ohm’s law, I calculated that 43 Ohm resistors are a good choice for all three colours.

After all the LEDs are lighting up when tested with a constant 3.3V output from a desk power supply, I use a Cat5-cable to connect the paper to two sets of header pins so I can test the work with the WEMOS D1.


Here you can see me testing the connectivity of components on bent paper. It appears that the angled copper-tape connections are the most fragile element of the design, especially the bent overlap that I have taped down with sellotape.

After powering the circuit with the desk power supply once more to test whether the LEDs still work with the cable bridges I add header pins to the end of the cables to provide a stable connection to the Wemos D1 mini microcontroller. I use colored heat shrink at the end of the header pins to identify cables with the respective LED color for more clarity if  debugging is required later.

The next step involves addressing all LEDs correctly with the Wemos D1 mini.

I had previously noted down the temperature ranges from the SHMAK manual (NIWA, 2008) and also added all values to the header comment of the testing code for easier reference later. This information also contains the colour of CAT5-wire strand, the digital pin connected, and the range of temperature as per SHMAK kit and the colour of LED (red/yellow/green) used to represent each state.

After some bugs in my code addressing all LEDs correctly (I ended up using digital ports D1–D8) I finally got all LEDs working with a simple looping sketch.

// Kaituhituhi-rua prototype - temperature

// blue wire - G

// brown wire          D7 - <5°C – 5°C - fair:5 (yel)
// green wire          D4 - 5°C – 9.9°C - good:8 (grn)
// orange wire         D2 - 10°C – 14.9°C - excellent:10 (grn)
// blue/white wire     D4 - 15°C – 19.9°C - good:5 (grn)
// green/white wire    D8 - 20°C – 24.9°C - fair:5 (yel)
// brown/white wire    D5 - 25°C – 29.9°C - poor:0 (red)
// orange/white wire   D6 - 30°C< - poor:-5 (red)


// LEDs
int ledPins[] = {D1, D2, D3, D4, D5, D6, D7, D8};

int ledState[8];

unsigned long previousMillis = 0;

const long interval = 1000;

void setup() {
  for (int p = 0; p < 8; p++) {
    pinMode(ledPins[p], OUTPUT);
    ledState[p] = LOW;
  }
}

void loop() {
  for (int c = 0; c < 4; c++) {
    for (int p = 0; p < 8; p++) {

      digitalWrite(ledPins[p], HIGH);
    }
    delay(500);


    for (int p = 0; p < 8; p++) {

      digitalWrite(ledPins[p], LOW);

    }


    delay(500);
  }

}

Next, I cut the paper into a smaller size and test how it fits in two different types of jars.

While fitting the paper into the jar I leave the microcontroller connected to evaluate how stable the solder and copper tape connections are. The power supply to the LEDs needs to remain stable while repeatedly inserting and removing the circuit from a jar. The LEDs indeed keep blinking which is a good sign. The smaller jar that was initially intended for the circuit has a pattern on the top and bottom of the glass which diffracts the LEDs and might make it hard to read.
The taller jar is clearer which makes it easier to see the LEDs, but from an aesthetical point of view, the circuit paper would have needed to be cut a bit larger to neatly fill the height of the jar.

In the end, I decide that both jars are suitable from a technical and practical perspective. The final choice of enclosure needs to be made after testing the prototype with the final code, showing only the LED of the respective temperature zone on.

High-Low Tech Group, MIT Media Lab. (2012, August 21). Paper circuits. Retrieved February 27, 2019, from http://highlowtech.org/?p=2505
NIWA. (2008, December 17). Habitat indicators of stream health. Retrieved February 27, 2019, from https://www.niwa.co.nz/our-science/freshwater/tools/shmak/manual/9habitat
Qi, J. (2012). The Fine Art of Electronics: Paper-based Circuits for Creative Expression (Master of Science in Media Arts and Sciences). Massachusetts Institute of Technology, Massachusetts, NE. Retrieved from http://web.mit.edu/~jieqi/Public/Jie_Qi_MS_thesis.pdf
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LED resistor overview

To make sure I supply the right amount of voltage for my Wemos D1 mini projects I need to know a little bit more about the kinds of LEDs I intend to use.

With the Wemos D1 mini typically supplying components with 3.3 V, I need calculate the approproate resistors for my various SMD LEDs.
An online web app (“LED Resistor Calculator,” n.d.) was very handy to find the right values. Below is a table of all the LEDs I have in my stash and the most important values from their data sheet for easy reference.

Type If Vf (max) R 3.3V
Red SMD LED red 70mcd
Gullwing  ZD2000 9061		 30.0mA 2.0V (2.5V) 43 Ω 43Ω (Datasheet)
Yellow SMD LED  yel 40mcd Gullwing ZD2005 9061 30.0mA 2.1V
(2.5V)		 40 Ω
Green SMD LED grn 100mcd Gullwing ZD2010 9061 25.0mA 2.2V
(2.5V)		 44 Ω
White SML-LX1206UWW-TR LED, QuasarBrite, White, SMD 20.0mA 3.5V (4.0V) – – Datasheet

Below is an image of how I use my coloured LEDs for the visualisation of water temperature in combination with resistors on a copper tape paper circuit (inspired by Qi, 2012 and High-Low Tech Group, MIT Media Lab, 2012).

High-Low Tech Group, MIT Media Lab. (2012, August 21). Paper circuits. Retrieved February 27, 2019, from http://highlowtech.org/?p=2505
LED Resistor Calculator. (n.d.). Retrieved February 28, 2019, from http://www.ohmslawcalculator.com/led-resistor-calculator
Qi, J. (2012). The Fine Art of Electronics: Paper-based Circuits for Creative Expression (Master of Science in Media Arts and Sciences). Massachusetts Institute of Technology, Massachusetts, NE. Retrieved from http://web.mit.edu/~jieqi/Public/Jie_Qi_MS_thesis.pdf