Tag Archive | "extreme"

Arduino and TM1640 LED Display Modules

Introduction

The purpose of this article is to demonstrate the use of the second (here’s the first) interesting LED display module I discovered on the dealextreme website, for example:

As you can see the display unit holds a total of sixteen seven-segment LED digits using four modules. However thanks to the use of the TM1640 controller IC

… the entire display is controlled with only four wires – 5V, GND, data in and clock:

Here is the data sheet for the TM1640. The board also ships with the 30cm long four-wire lead and fitted plug. Finally, there is a ‘power on’ LED on the right-hand end of the board:

Getting Started

Now to make things happen. From a hardware perspective – it couldn’t be easier. Connect the 5V and GND leads to … 5V and GND. The data and clock leads will connect to two Arduino digital pins. That’s it. The maximum current drawn by the display with all segments on is ~213mA:

So you should be able to drive this from a normal Arduino-compatible board without any hassle. Please note that the TM1640 IC does heat up somewhat, so you may want to consider some sort of heatsink if intending to max out the display in this manner.

From the software side of things you will need to download and install the TM1638 library (yes) which also handles the TM1640 chip. To simply display text from a string on the display, examine the following sketch:

Which will display:

The sixteen digit binary number in the module.setDisplayToString() line controls the decimal points – 0 for off and 1 for on. For example, changing it to

will display:

You can also display text in a somewhat readable form – using the characters available in this list. Displaying numbers is very easy, you can address each digit individually using:

where x is the digit, y is the position (0~15), and true/false is the decimal point. At this time you can’t just send a long integer down to the display, so you will need to either convert your numbers to a string or failing that, split it up into digits and display them one at a time.

In the following example sketch we display integers and unsigned integers by using the C command sprintf(). Note the use of %i to include an integer, and %u for unsigned integer:

And the resulting output:

Now you have an idea of what is possible, a variety of display options should spring to mind. For example:

Again, this display board was a random, successful find. When ordering from dealextreme, do so knowing that your order may take several weeks to arrive as they are not the fastest of online retailers; and your order may be coming from mainland China which can slow things down somewhat. Otherwise the module worked well and considering the minimal I/O and code requirements, is a very good deal.

Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, lesson, part review, TM1638, TM1640, tutorialComments (10)

Arduino and TM1638 LED Display Modules

Introduction

The purpose of this article is to demonstrate the use of some interesting LED display modules I discovered on the dealextreme website, for example:

They contain eight 7-segment red LED digits, eight red/green LEDs and also eight buttons for user input. You can get red or green display models. The units can also be daisy-chained, allowing up to five at once, and a short cable is included with each module, as well as some short spacers and bolts, such as:

The spaces are just long enough to raise the PCB above a surface, however to mount the boards anywhere useful you would need longer ones. You may also want to remove the IDC sockets if you want to mount the module close to the surface of a panel. This would be a simple desoldering task as they are through-hole sockets:

The board is controlled by a TM1638 IC:

This part seems to be a domestic Chinese product from “Titan Micro Electronics“. After a quick search the TM1638 isn’t available from Digikey, Mouser or the element14 group… so if anyone has a lead on a low-volume, reliable supplier for these – please leave a comment below. However here is a link to the data sheet – thanks Marc!.

Getting Started

Now to make things happen…

Hardware – Connection to an Arduino-compatible board (or other MCU) is quite simple. The pinouts are shown on the rear of the PCB, and match the fitting on the ribbon cable. If you look at the end of the cable as such:

The top-right hole is pin one, with the top-left being pin two, the bottom-right pin nine and bottom-left pin ten. Therefore the pinouts are:

  1. Vcc (5V)
  2. GND
  3. CLK
  4. DIO
  5. STB1
  6. STB2
  7. STB3
  8. STB4
  9. STB5
  10. not connected

For Arduino use, pins 1~4 are the minimum necessary to use one module. Each additional module will require another digital pin connected to STB2, STB3, etc. More on this later. Please note that each module set to full brightness with every LED on consumes 127mA, so it would be wise to use external power with more than one module and other connections with Arduino boards. After spending some time with the module, I made a quick shield with an IDC header to make connection somewhat easier:

Software –  download and install the T1638 library from here. Thanks and kudos to rjbatista at gmail dot com for the library. Initialising modules in the sketch is simple. Include the library with:

then use one of the following for each module:

x is  the Arduino digital pin connected to the module cable pin 4, y is the Arduino digital pin connected to the module cable pin 3, and z is the strobe pin. So if you had one module with data, clock and strobe connected to pins 8, 7,  and 6 you would use:

If you had two modules, with module one’s strobe connected to Arduino digital 6, and module two’s strobe connected to digital 5, you would use:

and so on for more modules.  Now to control the display…

The bi-colour LEDs

Controlling the red/green LEDs is easy. For reference they are numbered zero to seven from left to right. To turn on or off a single LED, use the following:

Using the method above may be simple it is somewhat inefficient. A better way is to address all of the LEDs in one statement. To do this we send two bytes of data in hexadecimal to the display. The MSB (most significant byte) consists of eight bits, each representing one green LED being on (1) or off (0). The LSB (least significant byte) represents the red LEDs.

An easy way to determine the hexadecimal value to control the LEDs is simple, image you have one row of LEDs – the first eight being green and the second eight being red.  Set each digit to 1 for on and 0 for off. The convert the two binary numbers to hexadecimal and use this function:

Where green is the hexadecimal number for the green LEDs and red is the hexadecimal number for the red LEDs. For example, to turn on the first three LEDs as red, and the last three as green, the binary representation will be:

00000111 11100000 which in hexadecimal is E007. So we would use:

which produces the following:

The 7-segment display

To clear the numeric display (but not the LEDs below), simply use:

or to turn on every segment AND all the LEDs, use the following

To display decimal numbers, use the function:

where a is the integer, b is the position for the decimal point (0 for none, 1 for digit 8, 2, for digit 7, 4 for digit 6, 8 for digit 4, etc), and the last parameter (true/false) turns on or off leading zeros. The following sketch demonstrates the use of this function:

and the results:

One of the most interesting features is the ability to scroll text across one or more displays. To do so doesn’t really need an explanation as the included demonstration sketch:

included with the TM1638 library is easily followed. Just insert your text in the const char string[], ensure that the module(s) are wired according to the module definition at the start of the sketch and you’re set. To see the available characters, visit the function page. Note that the display is only seven-segments, so some characters may not look perfect, but in context will give you a good idea – for example:

Finally, you can also individually address each segment of each digit. Consider the contents of this array:

each element represents digits 1~8. The value of each element determines which segment of the digit turns on. For segments a~f, dp the values are 1,2,4,6,16,32,64,128. So the results of using the array above in the following function:

will be:

Naturally you can combine values for each digit to create your own characters, symbols, etcetera. For example, using the following values:

we created:

The buttons

The values of the buttons are returned as a byte value from the function:

As there are eight buttons, each one represents one bit of a binary number that is returned as a byte. The button on the left returns decimal one, and the right returns 128. It can also return simultaneous presses, so pressing buttons one and eight returns 129. Consider the following sketch, which returns the values of the button presses in decimal form, then displays the value:

and the results:

Update – 21/05/2012

A reader from Brazil has used one of the modules as part of a racing simulator – read more about it here, and view his demonstration below.

Update – 08/02/2013

Great tutorial on using these with a Raspberry Pi.

These display boards were a random, successful find. When ordering from dealextreme, do so knowing that your order may take several weeks to arrive as they are not the fastest of online retailers; and your order may be coming from mainland China which can slow things down somewhat. Otherwise the modules work well and considering the minimal I/O and code requirements, are a very good deal.

Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, lesson, part review, raspberry pi, TM1638, tutorialComments (34)


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