Sunday, November 22, 2015

Mini plotter based on arduino

The technology is advancing very fast, allowing almost anyone to build CNC routers and 3d printers.
In the past years, a CNC machine was very expensive, the same was when the first 3d printers were released.
However, now it is relative cheap and easy to build one of those two.
Recently i found some tutorials on how to build a mini plotter with two dvd drives, one arduino board, and two L293D motor drivers.
Unfortunately i did not make photos on the building process, but for who is interested here is a detailed tutorial, similar with what i did:

What i did not had, was the servo motor, so my plotter could not lift the pen from the paper. However i don't think that is a problem, because i plan to mount a burning laser instead of a pen, to engrave text or cut slim pieces of plastic.
Here are two videos with the plotter in action:

I am planning on building a big version of this, with NEMA stepper motors.

Saturday, November 7, 2015

NFC shortcut button

What i enjoyed on old devices such as Psion series 5, HP Jornada 720, and other qwerty devices, was the shortcut buttons:

Those buttons allowed me to quick jump form word to calendar, or mail with a singe touch of a button.
I'm not exactly sure when those useful buttons were removed from devices, the last smartphone that had them, i think, was Nokia E90 communicator (which is unfortunately is no longer working due to broken flex cables).
The past is the past, we will never see those shortcut buttons again. 
However there is a way to have the same functionality on a today smartphone. The solution is NFC (near field communication) technology.
There are several apps on google play that allow the write of NFC tags. Those app can write a link, a shortcut to a file, or a shortcut to an application to a NFC tag.
The NFC technology works by power a small chip, which can store a few hundred of bytes of information, by radio frequency at 13.56 MHz.
In order to red or write a tag, that tag must be at a small distance from the nfc anthenna.
On smartphones the idea is to put the back of the phone on a tag and get the information from it or write it.
I saw in this a possibility of bringing back the functionality of those old shortcut buttons, but for this i needed to modify the tag by cutting its anthenna and then add a button which, when pressed, reconnects the anthenna:

Here is the complete tag with the button soldered:

I put this tag under a silicon case on the back of my note 4. But because the case was made of transparent plastic, and the modified tag didn't look very good, i decided to print some pictures with the application that the tag launches:

I simply put the paper on the tag just to mask it. I can write any application i want on the tag, so if i am browsing the web and want to quickly check my email, i simply press on the tag button and i'm on the mail.
And here is it, those very useful buttons are now back. I did this only with one button for test, but i can put several tag with buttons on the back of the phone.
Here is a video with the tag in action:

I will post a video with more buttons on the back of the phone.
Mini multimeter based on Arduino

The first development board i came in contact with was the Raspberry Pi, a few years ago. After building a tablet and a home automation system based on that board, i came across Arduino.
This because i had a work project that had to boot instantly (raspberry boot time is longer than a minute). It was a counting system for a conveyor, that can send the counted data to a server by ethernet. 
Arduino is different of Raspberry, first because of the programming language. For Raspberry the main programming language is Python, while for Arduino is C, the other main difference is that Raspberry uses an operating system, while arduino only runs C programs, it does not run an operating system. Arduino bassicly a single chip microcontroller.
The main advantage of this board over Raspberry is that this have 6 analog ports, without any analog-to-digital converter.
After a few weeks of playing with arduino, i finished the counter project, and i learn a lot about this board, but what sparked my interest was connecting a Nokia 3310 LCD and display a text.
You can find more information about this here:
Here is the pinout diagram:

As you can see, in order to make the display to work properly, i had to solder a 10 uf capacitor between the Vout and GND pins. However on some lcd models that capacitor is not really necessary.

While i searched for more details about the atmega 328 (the arduino microcontroller) i found the Reduino core:

It is just like a Arduino uno board, but as basic as possible, with the Atmega cpu and the crystal. Also this board can be powered with no more than 5 volts.
To program it it is necessary to connect it to an arduino uno board:

It is perfect for small devices, or automation systems where the space is very small.

After i ordered several of this small boards (they are also very cheap), and because i had a spare Nokia 3310 lcd, i decided to create a small portable multimeter.
This is possible thanks to the built in analog inputs which can directly measure voltage up to 5V.

So i got a BL-5C Nokia battery to power the reduino board, (it does not deliver 5 volts, but it power the arduino and the nokia lcd quite well).
A small switch is connected to the + of the battery in order to turn it on/off . The 4 wires are plug in the arduino uno for reprogramming. Here are a few pictures of the building states.

1 Ohmmeter

Arduino can measure, with the analog inputs, the voltage at the middle of two resistors.
The schematic is very simple:

The arduino reads the voltage at the selected analog pin (A0). This voltage cross the resistor which is being measured.
You can find the source code of the ohmmeter on google. Here is one example:

What i did was to modify the code according to the voltage supplied by the battery (arduino works with 5V, but my battery can supply only 3.7 to 4 volts), and add some lines to display the value of the resistor on the nokia LCD.

2. Measure capacitors

After the the the small device could measure resistors,  i decided to enhance it further by adding the posibility to measure capacitors.
The working principle is by measure the charging time of the capacitor.
The schematic and the source code are from here:
I modified the code, as was the case of the ohmmeter, and combine the two programs into one and upload them in the Reduino.

3. Voltmeter

The principle is simple since it is possible to measure voltage directly with the analog inputs. However there is the maximum 5V limit that can be applied to the input. So i used a 100 K ohm resistor. Here is the diagram:

The source code can be found here:

Again i modified the code to display the data on the nokia LCD and combine this code withe the first two, and the end result is a portable multimeter, which work quite good (there are limits in its accuracy), but for a quick measure is good, and very portable.

Here is a video with the multimeter in action:

This is the first version, i am going to make a plastic case for it and some sockets for probes.