The Making of an Indoor Pool Climate Controller

Photo by Fancycrave on Unsplash


This was a very interesting, yet demanding project (see the brief here) I undertook in April/May 2018 in my second-year course Electronics I. This project required us to create a collection of circuits that would work together to control the lighting, temperature and humidity inside a model indoor pool as well as control the number of people in the pool by closing the entrance if there are too many people. The project involved six parts and was therefore split between the six individuals in my group. These six components included the power supply, the bathing load, the internal lighting (designed and implemented by myself), the external lighting, the temperature control and the humidity control of the pool area. This solution we created could be scaled and used to model real pool systems, ensuring R & D costs decrease and many more people can afford pool control systems.

Technical Stuff

This is what each of these components entailed:

  1. Power Supply – This circuit involved suppling different voltages to each member’s circuit and having LED indicators showing if the supply is on or off. This was done using a standard FWBR circuit with capacitor-filtering and regulators.
  2. Bathing Load – This component required a counter circuit to count (in decimal) the number of people who have entered the pool (using a gap sensor). This counter should also stop counting and ‘not allow any more people into the pool’ if the counter count exceeded a specified number unique to each group (ours was 82). The output of this circuit was supplied to the internal and external lighting.
  3. Internal Lighting – This circuit has three LEDs as its output. The stage one LED is found in the external lighting circuit and is detailed in the next point, the stage two LED is designed to turn on when the bathing load is more than zero (achieved using a OR gate from the external lighting and bathing load circuit) or the light level is below a certain intensity (measured in lux). This change in light intensity is simulated using a cone of yellow filter paper. The light intensity of the circuit was measured using a photodiode. The stage three LED is designed to turn on if the bathing load is more than zero and a switch is flipped to on. This third LED represents flood lights for a possible competition at the pool.

    The block diagram I used for the indoor lighting
  4. External Lighting – This circuit has two LEDs as it’s output. The first being used as security lights and the second as lights for the parking lot. The security lights turn on when light falls below a certain intensity, represented using a blue cone of filter paper. The security lights also serve as the stage one light for the internal lighting system. Additionally, this circuit uses the PIN photodiode sensor. The parking lot lights turn on when light falls below a certain intensity and there are people in the pool, like the internal lighting. This circuit uses the PIN photodiode sensor.
  5. Temperature Control – This circuit is designed to keep the indoor temperature of the pool area between 26 and 29 °C. When the circuit is in ‘winter’ the circuit will try to keep the indoor temperature at 26°C, while in ‘summer’ the circuit will try to keep the indoor area at 29°C. This is done to ensue there is not such a great drop in temperature when pool-goers exit the pool area. This is achieved using a temperature sensor and DC fan.
  6. Humidity Control – This final circuit is designed to keep the humidity stable, this is measured using RH (relative humidity). In winter this value should be kept at 50%RH and in summer this value should be kept at 60%RH. This is implemented using a humidity sensor circuit.

    Blue – Power Supply (with external transformer). Red – Bathing Load. Green – Internal Lighting. Orange – External Lighting. Purple – Temperature Control. Yellow – Humidity Control. (Photo by Nic Reus in group 1)

How I Did It

Now that that technical stuff is out the way, here is the process my teammates and I went through to get this project up and running.

The project had to be designed, implemented and documented. This was supervised by our tutor for Electronics I, who was to meet us three times to consult on our progress and suggest improvements. For myself the design process started with researching LED circuits on YouTube and in our textbook (I will have another post on tips and links to useful web pages and textbooks for doing electronics projects).

Once I had got a general idea of how my circuit should work and the type of components that are best suited to making it work as it should, I implemented it on the circuit simulation software EveryCircuit and then Multisim. Thereafter, I acquired the components needed to test my prototype circuit from my school’s electronics store and built and tested my circuit to see how it behaved in real life and how this differed from the simulated circuit.

The Multisim simulated op amp circuit used to convert the input signal from 5V to 9V
The Multisim simulated stage 2 and 3 phototransistor LED lighting circuit

Once I had tweaked my real circuit resistor values and minor layout changes, I reimplemented in back in simulation and then acquired the final components to build my final circuit. My first design using op-amps didn’t work well with the light sensor I was required to use. This meant that late in the implementation process, I changed my design to use transistors to amplify the required current for the LEDs to shine. This designed worked well and so was the final design I used for my section of the project.

On the day the project was due, my friends and I went to Mantech, a supplier of electronic parts in Johannesburg to get last minute components for our final design and extra components in case something broke just before the testing period.

Group 1 working on their final implementation. (Photo by Nic Reus in group 1)

My teammates and I then presented our project, aiming to show off its strengths and shield (without lying) its flaws. Improvements were mentioned, but ultimately the project worked largely as was required, everyone’s system functioned individually and together. The power supply could run every component simultaneously and we had extra diodes for the rectifier in case they blew. The same went for the other individual circuits.

The next part of the project was to write a report on how each of our components functioned, the data we obtained to determine if the project worked as specified and how we analyse these results. I have linked this report here.

The report was not too difficult for me to do as I had documented my process and results along the way of making my circuit. Unfortunately, there was not much space to put in the diagrams and results we would have liked to, and we received a disappointing mark for the report as a result. This was a lesson in brevity we all learned the hard way.

What I Learned

We all learned a lot from this project. Most importantly how to structure the process of future projects. I also learned:

  1. Time management – How to plan projects over several months, making sure certain thing happen at the right time and what to do if they don’t happen.
  2. People management – Having a team of people that feel they are involved, have a purpose, can rely on each other and know what is required of them will achieve much more that a team that does not communicate or are a group of lone wolves. I was a bit of a lone wolf in this project at times. But this was because I knew I had to finish my section before implementing it in with everyone else’s circuits and no one really knew more about my section than I did. If this is the case, at least keep up with your team about your overall progress and ask them how they are getting along. Also keep the big picture and goal in everyone’s mind.In addition, consult with your tutor and other group’s members doing the same section as you. Maybe there is something you are not considering or having a mental block about. Whatever it is, keep the communication channels open.

    Photo by Priscilla Du Preez on Unsplash
  3. Having a plan B – This enabled me to not rely solely on my plan A design if it didn’t work as I wanted it to, this took a lot of pressure off me and proved vital by the end of the project.
  4. Decision making – At the end of the project, my plan A was not working well, and I gave myself a deadline to decide whether I should change to plan B. I reached that deadline and had to swallow my pride and try this second circuit plan. This was a hard decision that worked out in the end.
  5. To document my work – This sounds tiresome, and at times it is, but having a space to plan and document your work means all the information your need is neatly formulated in your head and you can make more informed decisions going forward. Documenting your work also allows you to easily recall your design process and data if you are required to do a technical report on your work later. At Wits, this was advised our lecturer and we were all given an A5 book in which to do this. Use it!

    Photo by Green Chameleon on Unsplash
  6. To have extra parts – These were important in case anything blew on the day of testing and we wouldn’t have to stand in the long queue at my university or travel to and buy more parts at Mantech.


The Electronics 1: Indoor Pool Climate Controller project I did in April/May 2018 was our first real opportunity to implement all the theory we had learned in the last year and a quarter. It was challenging, but with every challenge comes a reward. For us, this was the finished project that worked and the lessons and companionship we had gained along the way. I look forward to next semester’s course on microprocessors and the project that will come with it!