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The Alchemy Lab

Published on: | Author: Thomas Wimmer | Categories: 2016b, Projects

The Alchemy Lab – Professor Pooly’s Potion Plotting

This years topic for the course was “Scavenger’s hunt” – creating a puzzle/riddle that can also survive outdoors. After being introduced with several sensors and what the Arduino can actually do we quickly decided to include the four elements – water, fire, earth and wind – into our project. Some research and discussions later we agreed on building our own little alchemy lab which also fits perfectly with the four elements.


The story behind…

A long time ago in a long forgotten land a crazy mysterious professor and his faithful and inferior imp Hogsworth aspired eternal life. Day in day out they tried new invented recipes and brewed potions of all colors in an old laboratory up in an even older tower to finally achieve their goal of immortality. Sometimes their tongues would turn to gold, sometimes they grew new body parts, other times they shrank or grew and most of the time simply nothing happened – at least nothing they immediately noticed. One day they were sure to have finally found the right recipe which would make their lives never-ending. Greedy as the old professor was – already looking for the potion that would grant him immortality for way too long – he took the first sip. With a huge gulp he chugged almost the whole bottle but instead of eternal life he found … eternal death. The small Hogsworth might have been simple but not completely dumb. Seeing his old master being dead he decided to quit the potion brewing business immediately. But this sounds easier than it is. Imps of his kind need to be granted a potion of special kind by a stranger from foreign lands to be freed forever. So he was sitting in the chambers of the old tower waiting for a stranger to release him from his grim destiny, promising this person one wish (or just a hint, or maybe nothing but well it is still worth a try, isn’t it?). And who knows, maybe this poor fellow is still living his damned old life in the even older tower…

The idea

After hearing this sad story we had to help Hogsworth and build up his alchemy lab again.

So the question was how it is supposed to look and how we create a fun puzzle that can also be done within a few days. Some brainstorming later we eventually decided to split the project into four parts equal to the four elements. When completing all four parts the potion is brewed and the imp provides a hint to the next destination – therefore the next station of the scavenger’s hunt.


The basis of every potion is some kind of liquid. So we start of with water.

This part was mostly based on a riddle. The idea is to have three pipes where water can be poured in, but only one of them is the correct one. This part of the puzzle is based on simple physics – more precisely the principle of communicating vessels.

One of the three pipes is connected to a fourth one which contains a small ball. If water is now poured into the correct one the water level in the connected pipe will rise as well and the little ball will float up. If the water level is high enough the ball connects two wires and a circuit is closed. The ball is – of course – covered with copper and therefore conducted.


Now you might wonder how to find the correct pipe. We thought about a more or less difficult riddle. In advance, to solve this riddle Google or a major in chemistry might be helpful – but most likely you will need both.

  1. While burning I turn a fiery red.
  2. Correctly I shall be called Dihydrogen Monoxide, my place is left to a gas.
  3. Inhaling me will make people around you laugh.
####### SPOILER ALERT #######
Explanation: Because of the water symbol it should be obvious that water is supposed to be poured in one of the pipes. So the challenge is to find out which pipe is the correct one. Lithium which is a metal is turning red when it is burned. So the solution to 1 is Lithium which has the atomic number 3 in the periodic table. Therefore, water does not belong into pipe III. Dihydrogen Monoxide which is described in the second hint is H2O which again is water. The second part of this hint says that water is left to a gas. Lithium – on position III – is not a gas so water cannot belong in II – which would be left of III. Thus, water must be poured in I. As an additional hint 3 describes something that makes people around you laugh when you inhale it. As everyone knows, inhaling Helium changes your voice in a funny way making everyone laugh. Helium has atomic number 2 and is obviously a gas. As we know from hint 2 water is left to a gas, so left to helium at II – so again water belongs in I.

A friendly reminder: Keep in mind that water and electronics are usually not best friends. So on the one hand make sure that all tubes and pipes are waterproof and on the other hand place the Arduino and everything water-sensitive above all tubes and pipes – just in case.


This part which needs to be solved to brew the potion is wind-themed and actually quite simple. It follows a similar approach as Water. When a copper covered ball connects two wires we have a closed circuit. We used another pipe with a small hole in the bottom – big enough for a straw but too small for a ball to fall through. At the top of the pipe are two wires, which need to be connected to close a circuit. So the idea is to push the ball up the pipe with the pure power of your lungs.



Let’s come to the most difficult part we had to create. Earth is also the reason why we finished about 20 minutes prior to presenting our project.
But first the idea: The goal of this puzzle is to put the right gem on the appropriate panel. With sapphire, emerald and ruby we chose three of the most famous gems. Each of this gem has to be placed on one of five panels – surprisingly labelled with the numbers I, II, III, IV and V. If all gems are placed correctly the riddle is solved.


How to know where to put what? We thought about three one-liners to provide first the gem and then the position:

  1. I am royal therefore I come first.
  2. Dear to Saturn I stay right left of him.
  3. Born in May I belong in the middle.
####### SPOILER ALERT #######
1. Ruby is considered a royal stone and ‘I come first’ obviously means panel I. Ruby on I.
2. The word sapphire derives from a sacred language of Hinduism and literally means ‘Dear to Saturn’. Saturn on the other hand is the sixth planet in our solar system, so staying left of him means on position five. Therefore: Sapphire on V.
3. The birthstone of May is emerald and the panel in the center of five panels is the third one. Emerald on III.

And now to all the issues we had. We first tried to figure out how to see which gem is on which panel. With different weights of the gems we would have been able to find that out. So we experimented with Force Sensing Resistors (FSE) – which simply measure pressure. With different weights we can measure different pressures and therefore react to that. The problem though is that those FSEs need a lot of pressure to give a valuable result and we were not able to get anything small but heavy (e.g. lead) in any of the stores we went. So FSEs were disqualified (only took us 1.5 days to find out).

So we went on to a similar approach we used before: closing a circuit. We did some testing with sponges. If a sponge is squeezed far enough, two wires would connect and a circuit closed. With different sizes of sponges we thought we can influence the weight needed to close the circuit and therefore sense the various weights. Another couple of hours later we threw the sponges in the trash… the sponges unfortunately were too steady and the weight we had was not enough to squeeze them as strong as we needed.


We were sure we followed the right attempt. Another thirty minutes later of thinking we agreed on using cotton wool which is a lot less steady than the sponges we had. But how to keep the cotton wool in place and how much to use for which weight?
Long story short, we eventually found a way to close a circuit when putting a weight on a panel using cotton wool but we were not able to sense different weights. At least not a few minutes before the deadline.


As every experienced alchemist knows a potion is only good if it is boiling. So the idea was to make fire – or at least see if there is some fire. Temperature sensors are often quite expensive or have a maximum temperature that was not high enough for a simple lighter.


Our first approach was another principle of physics: positive temperature coefficient. If a metal is heated up its resistance increases. To test this we burned some resistors we found and measured the changing voltage which was actually a lot of fun and is what this course is all about – having fun with hacking.


Unfortunately the difference in voltage was not high enough and we changed plans. Luckily, Bernhard provided us with a temperature sensor which worked perfectly. So making a fire was finally possible.

The looks

For designing our lab we had three goals. First, the four parts should not look independent, but they are supposed to be one so that every part is equally important to master the potion making. Second, all wires should be hidden. Keep in mind, we are in a really old tower without any electricity. And finally, make the whole project look old and mystical.


As seen on the images, every part is built out of wooden boxes we cut with a laser cutter. They are then attached on a back plate with mystical engravings and the riddles for Water and Earth. All wires lead to the back of the plate and are attached out of line of sight.  

Putting everything together

After building all four puzzles and the back plate it was time to put everything together and make it one. We attached the boxes on the plate and hid all wires behind it. Above Fire we placed our potion that changed its color whenever one of the riddles was solved. That’s why we placed three RGB-LEDs underneath. This also helps the user to find out when a riddle is solved through visual feedback. Additionally, it has a fun effect.


The hint provided by the imp when he is happy and free (so when the potion is done) is provided by a LED. We placed eight LEDs, labeled with 1-8 (we were 8 teams in total) on the back plate. The LED with the correct number will light up when the whole puzzle is done.

Electronics and code

Due to the fact that the Force Sensing Resistors we wanted to use for Earth did not work as expected we ended up with one main technology: Closing a circuit.

As already mentioned, Water, Wind and Earth worked with closing a circuit by moving balls or pushing something down. It is as simple as it sounds. If the circuit is open there is no voltage and if the circuit is closed there is voltage. This can be measured with the Arduino and when using various pins the circuits can be differentiated.

For Fire we used a PT1000 Thermosensor which works perfectly to measure temperature. It has a 1000 Ohm resistor which is valid at 0° Celsius. With changing temperature the resistor changes and therefore a different voltage can be measured (for further information: Resistance thermometer). We took the initial value provided by the sensor and then constantly checked. If the value changed by a certain threshold we knew someone heated up the sensor and completed the task.

We used normal colored LEDs as well as RGB-LEDs. Normal LEDs have two pins. One for Ground one for Power. If there is power, the LED lights up. The more power, the brighter it is. RGB-LEDs work in a similar way, considering the brightness. But they have four pins instead: one for red, one for green, one for blue and one for Ground. Depending on how much power is provided for each pin the color can be changed – simple color theory.

How everything is wired and connected can be seen in this fritzing layout:


The documented code can be downloaded on github.

A video of the project can be seen on YouTube.

linked categories 2016b, Projects


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