Which between lemon and orange is the most acid (sour)?
The answer is obvious: lemon !
We, humans, can sense different tastes (bitter, sour, salty and sweet) thanks to our tongue. But how? Our tongue is covered of many small buds, each connected to more than 100 receptors that are also connected to our brain. So when our tongue is in contact with lemon, our buds will send a message to our brain and our brain will think: “Oh this is very acid!”.
Here is a funny video showing a baby trying lemon for the first time.
Human’s tongue (connected to the brain) is very good example of a biological sensor, as it can differentiate different tastes. The tongue is also able classify flavours from less tasty to more tasty (orange, for example, seems less acid compared to lemon).
Biological sensors are not the only ones that can sense and classify different “concentrations” of tastes. The Grove Water Sensor is an example of an electronic sensor which can detect water and differentiate different salt concentrations. But again, how? As you can see on the image, this sensor is composed of a grid of electrodes which can sense the presence of ions in water. Salt is mainly made of ions, so the Grove Water Sensor can easily make the difference between different salt concentrations in water.
So which between the human’s tongue and the Grove Water Sensor can best sense different concentrations of salt in water?
This is a question we (a team of bachelor students) tried to answer this week, by performing series of experiments.
So what were the experiments? First, we asked 30 people (mostly students) to try and classify cups of water with different salt concentrations (0, 1, 2, 3, 4 and 5g/L) from the lowest salt concentration to the highest. These people had 3 mins to perform this task, in the way they wanted. Also, in the experiment, we disposed 2 cups instead of 1, with the 3g/L concentration, to test human’s ability to recognise the same concentrations.
Before we started the chronometer, and to make sure they react to salt, we let them taste two cups, one filled with only water, and the other with water and the highest salt concentration they would encounter during the experiment.
Then, to compare the human’s salt concentration classification with the Grove Water Sensor we built a simple electrical circuit with this sensor connected to an Arduino Uno and a computer. Wait… what is an Arduino Uno? It is an electronic device that records data and sends it to a computer, thanks to an informatic code. So with this electrical circuit, we were able to read values given by the sensor, on the computer!
We dipped the Grove Water Sensor in the same water salted solutions as the human experiment, 15 times (to have a good amount of data for our comparison and analysis) and we picked up the sensor’s values (values decreased as the salt concentration increased).
Here is an image showing basically our both experiments:
And below are the graphs we finally obtained: The first graph shows the percentages of errors in ordering the cups (for humans), in function of the salt concentrations; and the second graph shows the values given by the Grove Water Sensor for each cups.
As you can see, very few of our human cobayes did not place the cups in the correct concentration order. That is why we can observe random mistakes on the first graph. Also, as you can see, the error bars for the 2 cups filled with the concentration 3g/L are not the same: that meen that some of the humans did not recognise that these 2 cups were filled with the same salt solution.
The second graph shows, in contrary, that the Grove Water Sensor did make precisely the difference between less salted waters and higher salted water. Indeed, more the salt concentrations in the cups increased, lower were the values given by the sensor, on the computer. Also, this sensor did recognise twice the same 3g/L concentration (that is why there is only one dot for 3g/L on the second graph).
So what can we conclude? Well, both humans and the Grove Water Sensor can sense several salt concentrations in water. But the Grove Water Sensor can best make the difference between different concentrations. As it gave us more values compared to the humans, who only placed the cups in the right order, the Grove Water Sensor is more precise. But, the values given by the sensor are more dispersed (the second graph shows only the averages of the values, as we tested this sensor 15 times for each concentrations). So that makes the electronic sensor less accurate compared to humans.
It would be interesting and fun to repeat this experiment again with more cobayes, more solutions of different salt concentrations and more than 1 Grove Water Sensor. Maybe with more samples, humans will be able to beat the electronic sensor?!
Read this article! If you want to learn more about the link biology-electronics:
And this blogpost about the brain’s power using the tongue:
Salteam twitter : @SALTyeam
Our resources:
https://en.wikipedia.org/wiki/Pull-up_resistor
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