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Makahiya – first tests

Hi everybody,
During this second part of the week, we had the opportunity to test several components of our project.

First, on Thursday, I tested the capacitive proximity sensor with a coaxial cable (~ 50cm long) and an aluminium plate. By chance, it worked immediately: no parameter tuning was needed on order to detect the proximity of my hand, in all directions and even through a 3cm wood table. Friday evening, I decided to do the same test but with a real plant this time (the calathea I’ve already told about before). I attached the coaxial cable to a leaf with some scotch and once again, it worked perfectly !! I was able to see how close my hand was from the leaf. And if I approached my hand of another leaf, it was not detected, which is good if we want to turn each leaf into a separate button (this is probably due to the fact that on the calathea, each leaf has a separate trunk) We can thus definitely validate the choice of this component.

On Friday, we received some of the components we ordered: the LEDs and all the stuff required to test them (resistors & transistors). We first tested the 2 types of LEDs with a laboratory power supply: they are really powerful, which is good. Then, we decided to try to control them with PWM. With a lot of help from Alexis, I soldered the different components required on the breadboard part of the Olimex P407 board while Tanguy wrote the code. First, it didn’t work and after some exploration, Alexis found a short circuit between 2 pins. Once it has been removed, it worked perfectly well. We had time to test only one of the 2 LEDs. Before taking the final decision about the leds, we want to test with the optical fiber. This will be done as soon as we receive it.

Next week, we have to do the schematic of our board. And I would like to write some code in order to detect how close my hand is from the sensor (up to now, I’ve just visually analysed the graph).

PS: I forgot to say, I’ve bought a new plant yesterday: a banana tree. I hope this species will move less than the Calathea. Answer on Wednesday.

Makahiya: many changes and components search

Hi everybody,

As Tanguy said, this week has seen many changes in the definition of our project. Indeed, Alexis suggested to use a real living plant. Obviously, this choice adds several difficulties: a true plant needs water to live and thus we’ll have to design a waterproof product. Moreover, a real plant grows which can be a problem as we want to put wires on leaves. Alexis and us made some research to find an appropriate plant, one which keeps its leaves all the year long, that grows as slowly as possible and has quite big leaves. Tanguy already told about the stabilized plants so I won’t explain it again.  Yesterday afternoon, I went to Truffaut in order to have a better view of the possibilities. I exposed our needs to the vendors and they showed me several plants. A Yucca is too rigid for our project, and another plant that I don’t remember the name has too many small leaves. In this shop, they didn’t have banana tree, unfortunately,which was one of the suitable plant we had found. I finally decided to take a Calathea. It will at least help us to size our project.

This week, we have also begun to look at the components that we could use. We are almost certain to use Flexinol in order to make the leaves move. It will probably be the main factor that will affect the battery size. For the proximity detection, Lélio (from Expelliarose) lended us their magic sticks so we can see how they used the capacitive sensors. For now, the most suitable chip I’ve found is the PCF8885, made by NXP. It can have up to 8 inputs and 2 chips can be connected in order to get up to 16 inputs. Moreover, it’s clearly stated that it’s possible to use remote sensing plates. We still have to check the minimum and maximum dimensions of the sensing plates before validating this choice.

Next week will be mainly dedicated to components selection.