Fruit Computer Laboratory

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Making a computer with fruits



Descripción del proyecto / Project description

El laboratorio temporal establecido durante el taller "interactivos? - ciencia de garaje" durante el 28 de enero al 14 de febrero del 2009, investigó cómo el material orgánico (frutas) podría emplearse como soporte para almacenar información binaria, [ y cómo éste a la vez podría ser instrumentado para la construcción de dispositivos lógicos, que en suma, conforman los elementos básicos de una computadora.

The temporal laboratory initiated during "interactivos? - garage science" workshop between Jan . 28 - Feb.14, 2009 investigated how organic material (fruits) could be used for representing binary information and how it could be possible to use it for implementing logic decision devicesweb b, that in sum, constitute the building blocks of computers.

Inicio del proyecto / How the project started

Este proyecto comenzó con la idea de crear un experimento colaborativo que hiciera reflexionar sobre la naturaleza de la máquina computacional de una nueva forma, proponiendo explorar la idea de crear una computadora a partir de frutas.

Un factor inicial decisivo del proyecto consistía en encontrar una propiedad química presente en las frutas que pudiera ser usada como representación de información binaria. Esta propiedad química debería ser reversible, esto es, que permitiera que la información pudiera ser programada y reprogramada más de una vez.

A través del foro del proyecto (, Andreas propone emplear los niveles de pH. Esta idea fue tomada y explorada a todo lo largo del taller.

This project started as a thought-provoking experiment to raise questions and reflections about the nature of the computer. It proposed to create a collaborative experiment to explore the idea of constructing of a computer with fruits.

An initial and decisive factor of the project was to find a chemical property of fruits that could be used for storing binary information. This chemical property was to be reversible, this is, that it  could allow for programming and reprogramming binary information more than one time.

While reading the project's forum Andreas proposed to consider the pH levels of fruits. This idea was taken and explored throughout the workshop.

Estado actual y metas futuras del proyecto / Present state and future goals of the project

En la actualidad el proyecto ha evidenciado la posibilidad de "programar" y "reprogramar" un bit de memoria orgánica al agregar gotas de limón o de mandarina, mostrando que este proceso es reversible.

En un futuro se plantea implementar una memoria orgánica de 88 bits que permitirá programar una palabra de 10 caracteres. Al observar un mensaje grabado a lo largo del tiempo se podría observar de qué manera la información es sensible (o no) a los procesos de degradación natural.

Paralelamente al proceso de construcción de una memoria orgánica, el proyecto busca continuar explorando las posibilidades de implementación de una unidad lógica basada en cambios de pH.

Presently, the project has evidenced the possibility to program and reprogram a bit of organic memory while adding drops of lemon or mandarin juices, showing that this process can be in fact reversible.

The future goal of the project consists of building an organic memory composed of 88 bits. This state will allow to make ,read or write a 11 character word (just enough to write the "hello world" message), allowing to experiment with the natural processes of degradation and to observe how this processes affect (or not) the storing of information. number theory homework

Parallel to this, the project continues to explore the possibilities of building an organic logic gate based on pH changes.

Notas de laboratorio / Laboratory notes

See also a collection of lab notebook images in

pH and what we have learned about it (02.02.2009 - 02.12.2009)

pHseems at first a very metaphysical concept (starting by its name), but it has some graspable characteristics:

pH is a measure related to the acidity or basicity of a solution. Solutions with pH levels lower than 7.0 are considered acid, whereas solutions with pH levels higher than 7.0 are considered basic (alkaline). Solutions of 7.0 pH are considered neutral.

                          Acidic  <    7.0    >  Basic


The following are approximate pH ranges of various fruit juices and substances:

        2.0-2.5       2.7-3.5        3.0-3.8           3.8-4.3       4.5-5.2         5.8-7.0          6.5      7.34-7.45        9-10          

       Lemon      Orange      Mandarine     Apple(red)    Banana     Green peas     Milk        Blood       Hand soap  

Living systems are very sensitive to pH levels. In order to survive, a system must maintain an internal balance between acids and bases. This process is known as
acid-base homeosthasis. Therefore, the concept of pH seems to be directly associated with the conservation of life.

Mathematically, it is defined as a (minus) logarythmic expression, that is dependent on the concetration/activity of Hydrogen ions (H+) present in a given solution.

Since pH is a logarithmic scale a difference of one pH unit is equivalent to a ten-fold difference in hydrogen ion concentration.

More info: [n]
pH measurements can be practically obtained with the use of special glass electrodes known as

Reversibility (02.05.2009)

We have succesfully experimented with changing back and forth the pH value of a solution. Just by adding a few drops of a specific solution to a base solution the pH changes. Then, by adding some drops from the base solution the pH can be reversed to the first state.

To obtain negative changes in the pH scale seems to requiere less drops than positive pH changes (02.05.2009)

We have observed that for creating a positive change in the pH concentration, let's say, from changing from 2.5 pH (lemon juice) to 3.0 (mandarine juice) we need to add a lot more drops than for creating a negative change, that is, for going back from 3.0 to 2.5 levels.

We keep experimenting as the reasons for this fact are still unclear to us. It could also be the result of some mixed-up in our measurements.

Why we have selected two fruits with close pH values (02.05.2009)

We also observed that when the pH values of two different substances were more afar from eachother in the pH scale (lemon juice and tea for example), the more drops we had to add to the solution to make a reversible change in the pH concentration. For this reason we selected two fruits with close pH levels (lemon and mandarine) for building our first bit of organic memory.'

Experimenting with conductive electrodes and why this option has been left aside (02.06.2009)

As commercial pH electrodes are expensive and not so easy to find (average 60 euros, and mostly available in specialized stores) we began experimenting with alternative ways to replace them. '

We found that there is a direct relation between conductivity of a given solution and its pH value, so we decided to experiment building our own electrodes for measuring conductivity. '

After trying different sizes and forms our measurings varied but they didn't get reliable enough for inferring the pH concentration. '

It seems that home-made conductive electrodes tend to create a small electrical potencial in the terminal points, and it seems to change gradually over time, in turn affecting the actual measurement. Thanks Yago for pointing out this fact. '

We decided to buy a pH meter (70 euros at La Tecnica industrial S.L. on San Bernardo street). A pH meter is composed of a pH electrode attached to an integrated circuit that amplifies and converts the analog measurement and sends the information to a liquid crystal display.'

First experiments with chitosan (02.09.2009)

We are trying to make a pH sensitive gel that could be the base for our pH sensitive logic gate. We are experimenting with Chitofort, a commercial version of chitosan that is sold at nutrition stores as a fat attractor. Thanks Carla for finding about it. '

No great results so far.

Difficulties extrancting information from the pH meter (02.11.2009)

We are facing the problem of how to obtain information from the pH meter without afecting the measurement at the same time. pH meter uses ICL7126 analog to digital chip (datasheet) that sends data to a liquid crystal display (LCD).

To control the state of the different segments of the LCD the chip uses a signal frequency known as Back Plane (BP). When a particular segment is in phase with the BP frequency the segment is off, otherwise the segment is on. Julian Bleecker and Yago Torroja have been helping us with this.

We are experimenting with the use of optocouplers to read from the chip without affecting the measurement.

Fruit computer generating discussion in the DIYbio group discussion board (02.12.2009)

Kelly Andres has suggested the fruit computer lab in the DIYbio group discussion board. An interesting discussion is taking place. Thanks a lot for all the comments and suggestions.

Constructing pH electrodes from Christmas-tree ornamental balls (03.16.2009)

Renato Ianhez ( has written us pointing to this article mentions the construction of a pH electrode from a Christmas-tree ornamental ball. We are starting to experiment with this possibility.

Thanks Renato

Finding Christmas-tree ornamental balls in March (03.30.2009)

I innitially thought that getting Xmas tree ornamental balls in March was going to be a bit of a challenge. But I was wrong. I have found half a dozen of places here in Bogotá that still carry them. The actual challenge has been in fact to find the ones that are made of glass. It seems that they are becoming extinct, being replaced by plastic ones. Children are safer, parents are happy but pH memories will need to wait a little bit more.

Primeras aproximaciones a la implementación de una memoria orgánica binaria y como funciona? / Our first approach to implementing an organic binary memory and how it works

fruit computer lab // programming the organic memory // lemon and orange //

Selección de los niveles de pH de dos frutas diferentes como representación de información binaria

Las medidas de pH de dos frutas diferentes son seleccionadas como representación de información binaria. Se han seleccionado el limón y la mandarina, dos frutas de pH cercanos. Esta selección se ha hecho en pro de facilitar la “reprogramación” de la memoria con un número discreto de gotas.

Medidas de pH ubicadas en el rango de pH del limón (alrededor de 2.5 - 2.0) son consideradas como un cero lógico, mientras que medidas ubicadas en el rango de pH de la mandarina (3.0 - 3.8) son consideradas como un uno lógico. Estas medidas son obtenidas a partir de un electrodo de pH y buscan ser transferidas a un display para indicar un cero o un uno de acuerdo con la lectura.

Al agregar gotas de una fruta u otra se hace posible “reprogramar” el bit de memoria cuantas veces se desee (o hasta que el tamaño del recipiente lo permita).

                  Limón                                                                      Mandarina

      rango de pH: 2.0 -2.5       rango de pH: 2.5 - 3.0       rango de pH: 3.0 - 3.8
     |||||||||||||||||||||||||||||||||||||       ||||||||||||||||||||||||||||||||||||||      ||||||||||||||||||||||||||||||||||||||||
       →            0            ←       zona de "lógica difusa"      →             1               ←

Selecting  pH levels of two different fruits as representation for binary information

The pH value of two different fruits is selected for representing binary information. We have selected two fruits with close pH levels (lemon and mandarin). This selection has been made to facilitate the programming and reprogramming of the organic memory by adding a few number of juice drops.

Measurements located in the lemon pH range (2.5 - 2.0) are considered as logic zero, whereas measurements located in the pH range of mandarins (3.0 - 3.8) are considered as logic one. These measurements are currently obtained with the use of a pH meter. We are working the way to transfer them to a seven segment display that will show a zero or one according to the measurement.

By adding drops of one juice or another it is possible to program the bit of memory as many times as desired (or at least, until the recipient is full).

                  Lemon                                                                           Mandarin

         pH range: 2.0 -2.5              pH range: 2.5 - 3.0                pH range: 3.0 - 3.8
|||||||||||||||||||||||||||||||||||||         ||||||||||||||||||||||||||||||||||||||        ||||||||||||||||||||||||||||||||||||||||
       →        logic  0       ←              "fuzzy logic" zone             →          logic 1        ←

Documentación / Documentation


First day, visiting the grocery store.


Conversations begin with collaborators. Creating a theory for organic memory system for the fruit computer and an organic transistor which can make logical AND decisions.


This page shows a direct relation between pH levels and conductivity of a given solution. We began experimenting with the fabrication of our own electrodes for measuring conductivity.


Experimenting with moisture sensor as a possibility to infer conductivity and therefore pH levels. Thanks Hernani.


Marc measuring fruit resistivity.


Reading conductivity from the electrodes.




New idea emerges and bocadillo de calamares at Museo del Jamón.


Comparing lemon and tea pH values.


using processing and arduino as tools for measuring conductivity


Carla testing the electrodes.


We have been following an open lab notebook during the process. Notes has been transfered here and images can be seen here.



Change in conductivity caused by one drop of lemon


a drop of water in the solution creates no difference in conductivity



Idea for making a logic gate using a pH sensitive gel based on chitosan (thanks Marc!).

fruit computer lab / the day we hacked the pH meter

Hacking the pH meter. Thanks Dani!.



Yago, Andreas.


Chitofort is a commercial version of chitosan. We are experimenting with it, trying to make a pH sensitive gel. No succesful results so far.

Tecnologías y herramientas / Technologies and tools

Electrodos de conductividad

Químicos de calibración de pH

Papeles indicadores de pH

Arduino y Processing como herramientas para medir conductividad

DIY electrodes for measuring conductivity

pH meter

pH calibration chemicals

pH sensitive paper

Arduino and Processing as tools for measuring conductivity

Autor del proyecto / Project's Author

Alejandro Tamayo

Colaboradores / Collaborators

Andreas Puck

Carla Capeto

Kelly Jaclynn Andres

Johanna Villamil

Yedra Ayuso




Agradecimientos / Special thanks to

Marc Dusseiller - our materials science advisor

Adrian Bowyer - for a very inspiring "pH sensitive gel" disertation on a napkin

Yago Torroja - for helping us in better understanding the intricacies of the pH meter

Andy Gracie - for suggesting a very nice mixing alternative

All other groups with whom we shared the garage space - for constant inspiration and motivation

Enlaces / Links

Foro de inicio del taller / workshop forum

Desea colaborar? / Want to help?

Son necesarias contribuciones en estos campos:

Cómo construir electrodos de pH de bajo costo?

Información, sugerencias de cómo fabricar geles caseros sensibles al pH?

Suggestions for building low budget pH electrodes?

Suggestions for making pH sensitive gels at home?

Contacto / Contact:



Desea iniciar su propio laboratorio? / Do you want to start your own lab?

Quizás las notas de esta wiki hayan sido de inspiración y usted está pensando en iniciar su propio laboratorio para explorar la construcción de un ordenador a base de frutas. Si es el caso y tiene alguna pregunta o si simplemente desea contarnos de sus progresos puede ponerse en contacto con nosotros:



Perhaps the notes on this wiki have inspired you to start your own fruit computer lab. If you have any questions or want to tell us about your progress, you can contact us: