MXLED.exe

MXLED is a simulation of the LED matrix that can be used with a microcontroller simulator on Micro .exe. With MXLED, the system design of LED matrix, commonly referred to as Running Text, or many also call it Moving Sign, be more easily implemented.

MXLED on this version provides the size up to 200 columns x 80 lines. With this size, we can perform simulations for the LED matrix which suffice to needs that more real.

Enlarge the size of the matrix on this version is done by reducing the size of the LED to be only of 10 x 10 pixels. However, if we use monitors with size 1360 x 768, then size that can be displayed only about 135 columns x 64 lines.

MXLED

Arrange LEDs as matrix

MXLED is a simulator of the circuit matrix of LEDs. With this simulator, we can try to program the LED matrix controllers even without the hardware. MXLED made LED matrix by arranging the LEDs on the vertical lines and horizontal lines. We must provide the number of rows of horizontal lines (we make eight lines). Then, we also make as many vertical lines of columns. Arrangement of vertical lines and horizontal images are as follows:

Vertical and Horizontal Line

Lines of vertical and horizontal are not connected. Then, at each meeting point between the vertical and horizontal lines, attach a LED by connecting its anode to the horizontal lines and its cathode to the vertical lines. Installation of these LEDs are as shown below:

Installation of LEDs

By installing LEDs as above, the light up LED is the LED where the anode is connected to the horizontal lines which is high (1) and the cathode is connected to the vertical lines which is low (0). There is only one low vertical line at a time, while other line must be kept high. This low vertical line we refer to as the active column. Unlike the vertical lines, horizontal lines consisting of eight lines may has high or low value without having to pay attention to the other horizontal lines.

Horizontal Control

To give the voltage on this horizontal line, we can not directly connect it to port. This is caused by the need for large electrical currents. Therefore, horizontal lines are the powered using a PNP transistor as shown below:

The power supply for the horizontal lines

Each horizontal line given a transistor like the picture above. In this way, to make the horizontal lines can give the current to the LED, then the base must be low state (0). Meanwhile, if the base was given a high state, then the line could not provide current to the LED.

Vertikal Control

As horisontol lines, vertical lines can not be controlled directly using the port. This is caused by the large amount of current that must be sunk into the ground. Therefore, we can use the NPN transistor to sink current from these vertical lines. Way of installation is as shown below:

Vertical line current sink

Each vertical line is controlled using a transistor as shown above. If the base was given a high condition (1), then the line (column) will be an active line. Conversely, if the base were given the condition of low (0), then the line becomes inactive column.

As already mentioned above, there is only one column that should be active, while the other columns must be inactive. There are many ICs that output works like that. One of the cheapest is the 4017.

Columns control using IC 4017

Too bad that this IC only has 10 outputs. Thus, we can only make the controls to 10 columns

Relax, we can use other tricks to extend the control capabilities of this 4017. The trick is to make the block columns. The columns are grouped into block of columns. Each block columns consists of 10 columns. The columns in each block columns are numbered from 0 to 9. So, column 0 is the column 0 of block 0, column 10 is the column 0 of block 1, column 21 is column 1 of block 2, and so on.

Each base of the column with the same number are combined into one and is controlled by an output of 4017. For example, the base of the column 0 is connected to the base of the column 10, column 20, column 30, and so on. Then the bases which have become one, controlled by the Q0 of 4017.

Block Columns

From the picture above, we can see that although the base of column 0 and column 10 are controlled concurrently, but the column that can sink current is only the column with the active block. Seen that way of controlling the “column” or “block columns” is the same. If the number of block columns is only a few, then the controlling block of columns can be done directly using the port of the microcontroller. However, if the number of block columns is quite a lot, then the block columns can also be controlled using the other 4017. So, we develop a multilevel 4017, ie 4017 units (control column) and 4017 tens (the controlling block of columns). And if the number of block columns more than 10, then we can make the next level, ie 4017 level in the hundreds.

To cascade 4017 as above, is by connecting the carry output of 4017 units level as the input clock for the 4017 of tens level. And if there is 4017 of hundreds level, then the carry output of 4017 of tens level is used as the input clock for the 4017 of hundreds level. And so on. While the reset input of all of 4017 are combined into one. Thus, the overall control system only requires two lines for columns control, ie the input clock (clock input for 4017 of unit level) and the reset input (composite of all reset of 4017). Thus, the preparation of the LED matrix is exactly the same as the MXLED simulation.

Power Current Calculation

From the explanations above, we can see that there are three kinds of transistors viewed from the position. First is the row controller transistor, second is the column (unit) controller transistor, third is the column block (tens) controller transistor. Of course this calculation assuming that the number of columns are not more than 100 columns.

Calculation of the row controller transistor current

If each LED using a current of I, then the total maximum amount of current through the line control transistor is I x number of columns. For example, if each of our LEDs designed to use 5mA current and the number of columns are 30 columns, then the row controller transistor should be able to drain 5 x 30 = 150mA current.

The next question is, what is the value of collector resistor of the transistor?

To answer these questions, we should see the path of current from the power supply to get to the ground. First, the power supply current enter the PNP transistor through the emitter to the collector. Then passes through the collector resistor, then continues to enter into LED, enter into the collector of column controller, then enter the collector of the block columns controller.

If the power supply used is 5V, how much is the clamp voltage across the resistor? The voltage across the resistor is 5V – V on LED – VCE line controller tansistor – VCE of column controller transistor – VCE of column block controllers transistor. LED clamp voltage is typically about 1.7 V, but there are some types of LEDs which have a clamp voltage of up to 3V. While VCE transistors in saturation state is typically around 0.3 V. We assume that we use a regular LED with a clamp voltage of 1.7 V. Thus, the voltage across the resistor pin is 5 – 1.7 – (3 x 0.3) = 2.4 V.

Once we know the clamp voltage at the collector resistor of the line controller transistor, to calculate the magnitude of the resistor is R = V / I = 2.4 V / 150mA = 16 ohms. Too bad that we might be difficult to obtain this value of 16 ohms. So we can use a slightly lower value, eg 15 ohms, so that the LED current will be slightly higher, or use a little higher, for example 18 ohms, so that the LED current will be slightly lower.

Things should be kept on the LED matrix design like this is, that these calculations is the calculation of the current if the scanning is running. If scanning is not running, then a current of 150mA will be entered on one LED alone And currents of this magnitude would likely destroy the LED. So, we must take precautions so that the current should only flow if scanning process has been running. A little good news is, if we use the MCS-51 as a controller, so when the reset (the scanning process is not running) port is always in a state of high. So, if the base of line controller transistor is connected to the MCS-51 port, so it can be sure that the current will not flow to the LEDs on the reset state. However, you must ensure that the program will not hang. Because if the program hangs and stops the scanning process, then it means disaster for your LED matrix. And if you are not sure that your program can run smoothly, then you can reduce the LED current so that even if the scanning process is not running, current flows are still small enough to be able to be borne by one LED.

To calculate the base resistor value of the line controller transistor, we only consider the transistor to work as a transistor switch, which is so current that flows is the saturation current. With the calculation of the collector current of 150mA, then we can use the C9012 transistor that has a current gain of about 150. We can take a value of 100 to make it more secure. With the gain of 100 and the collector current of 150mA, then the base current should be about 1.5 mA. Clamp voltage at the base resistor is approximately 5V – VBE, where VBE is about 0.7 V. Thus, the clamp voltage at the base resistor is about 4.3 V. Thus, the base resistor value is 4.3 V / 1.5 mA = 2K8. And again that this value is not available values. So we could slightly reduce the value to the nearest number of available, namely 2k7.

Calculation of the column controller transistor current

Column controller will sink as much current number of rows in that column. And we have determined that the number is eight lines. If we have determined that the LED current is 5mA, then the maximum current to be sunk by the column controller transistor is 8 x 5mA, which is 40mA. With the value of this, we simply use the C9013 transistor to control the column. The Gain of C9013 transistor is also about 150. And as before, we take saver value to 100 only. With the gain of 100 and the collector current of 40mA, then the base current in the column controller transistor is 0.4 mA.

Clamp voltage at the base resistor of the column controller transistor is the output voltage of 4017 minus 2x the VBE voltage. If we use a 5V power supply, then the output voltage of 4017 is approximately 4.8 V. Thus, the clamp voltage at the base resitor is about 4.8 – 2 x 0.7 = 3.4 V. Thus, the base resistor value of the column controller transistor is 3.4 V / 0.4 mA = 8K5. And again, this value is not available values. So, just use the 8K2.

Calculation of the block columns controller transistor current

The block columns controller transistor will sink as much current in the column controller transistor x 10, which is 10 x 40mA = 400mA. From the datasheet, C9013 has a maximum collector current of 500mA. So, we can still use the C9013 to controll block columns.

Clamp voltage at the base resistor of the block columns controller transistor is the voltage used to control this transistor reduced by 1x VBE. If we also use 4017 to control the block column, then the clamp voltage across the base resistor of the block columns controller transistor is approximately 4.8 – 0.7 = 4.1 V. Thus, the value of the base resistor of the block columns controller transistor is 4.1 V / 4mA = 1K.

That’s it. Happy trying

In the example in Showing images on LED matrix using simulator, the note is displayed as an image. First we create a text image, then we create a constant from the text image. After that it displayed as an image.

Displaying text in this way is only appropriate if the text to be displayed is short. In addition, the displayed text will not be changed anymore. If the note to be displayed is a long text, or text that is displayed will be changed, then there is a better way than that way.

A better way is as follows: First, we create a character constant. In the example here, we make a character constant of 8 rows x 5 columns character size. The character constant was created using Karakter.bmp that you can edit to fit your desires.

Once we get a constant character, by compile the Karakter.bmp using ImgTable.exe, then every time we will display the text, we do it by reading the text character-by-character. Each character is read, then displayed by looking at the character table. In this way, we can display any article and can be changed while the program is running. Of course you have to create a procedure to change the text to be displayed if you want to replace it.

Unfortunately the program listing only writen in assembly language. So, if you prefer to use the C language, please do the conversion yourself

If you want to try the example program using MXLED, do the simulator settings as in Showing images on LED matrix using simulator

Good luck

There are six sizes provided by MXLED, ie 8 × 16, 8 × 32, 8 × 48, 16 × 16, 16 × 32, and 16 × 48. For each size there are two choices of orientation, ie landscape and portrait.

Control signals only use bit.0 and bit.1. Bit.0 used to reset the counter, while bit.1 used to increase the counter.

Data signal used to determine which LED where lit and LED where off. For each time, there were only eight LED that are controlled, which LED on the current column. To determine which columns is active, we use a counter. At the time counter is reset, then the column 0 is active. then if we provide the clock signal, the signal on bit.1, then the active column will move to column 1. Then if given the clock signal again, the active column will be column 2. and so on.

There are two choices of the clock signal, ie the L to H transition or the H to L transition.

The arrangement of the columns of LEDs depends on the size and orientation. For landscape orientation, then the left column is a lower column and the right column is a higher column. This applies to the size of 8x. As for the size of 16x, then the LED array is divided into two blocks of rows. The first column number of the second row block is the column number of the last column of the first row block plus 1.

More details are as follows:

16 x 16

Row 0..7 : 0  1  2  ......15

Row 8..15: 16 17 18 ......31

16 x 32

Row 0..7 : 0  1  2  ......31

Row 8..15: 32 33 34 ......63

16 x 48

Row 0..7 : 0  1  2  ......47

Row 8..15: 48 49 50 ......95

For each block row, bit.0 will control the LED at the top, while bit.7 will control the LED at the bottom.

For portrait orientation, we divide the LED into a column or a block of columns and rows. Counter will determine which row is active. Top row is row 0, and will be active if the reset signal is activated. The active row increase along with the clock signal acquisition.

For the 8x size, column 0 is the leftmost column and activated by bit.0. Whereas column 7 is the rightmost column and activated by bit.7

Rule for the 16x size could be analogous to the position of landscape orientation.

MXLED simulated on the system to work like a real matrix. If we managed to change the active row or column slowly, then it can be seen only eight moving lights jumping around. However, if the changes is fast enough, then the lit changes of the LED will be seen steady not blinking. So the simulation MXLED will feel like a real LED matrix.

You can see examples of the use of this MXLED in the example Showing Images on LED Matrix using Simulator

Controlling the LED matrix is actually almost the same as controlling seven segment. The difference is that the LEDs of seven segment are organized into seven sections which could form the figures. While the LED matrix, LEDs are arranged into a matrix that can be referenced by column and row. The columns on the LED matrix can be equated with the digits on the seven segment. While the lines on the LED matrix can be equated with LED a through LED g plus a decimal point LED on seven segment. Thus between the seven segment and LED matrix is basically the same, especially if the number of rows are only eight.

Then how to display images on the LED matrix? Yes basically the same as displaying the numbers on the seven segment. If you are already familiar with how to display data on the seven segment display using the buffer as is done in discussion about seven segment in the Easy and Fun Learning Microcontroller book, in which to display data on the seven segment, all we have to do is fill the display buffers, then to display image on the LED matrix, all we need to do is also just fill data on corresponding display buffers.

In the picture above, the size of the LED matrix that we use is 8 rows x 32 columns. This size is equivalent to seven segment which the number of digits are 32 digits. Thus basically we need a total of 32 bytes of display buffers. The LEDs on the top line we associate with bit 0 of port and successively LEDs on the lines below to bit 1, bit 2, and so on until bit 7. To make a LED lit on a particular line, then we need only fill the correlated bits with 0 or 1 depending on the configuration of the matrix that we use, active low or active high. For ease of understanding, we usually use active high so to lit the LED on the top line then we have to make the bit 0 to has the value of 1.

As an example, consider the logo below. The logo size is 32 x 32. Therefore, the logo may not be displayed on the LED matrix with the size of 32 x 8 at once. To display it, we have to split the logo into four parts. After that we have to show four parts one by one.

To the left of the logo there is a number from 0 to 7 and repeated up to four times. While above the logo are the numbers from 0 to 31. These figures will show us how to display the parts of the logo on the LED matrix. The figure above the logo shows the buffer index, while the figure at left of the logo shows the bit position. Thus, to show the first part of the logo (the top), then the buffer [0] must be filled with data 11111111b, buffer [1] = 00000001b, buffer [10] = 00011001b, and so on.

  0.        1.        2.        3.
  01234567890123456789012345678901
0 ©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©
1 © .............................©
2 ©..........©©©©..©©©©..........©
3 ©........©©©©©©..©©©©©©........©
4 ©......©©©©©©©©..©©©©©©©©......©
5 ©.....©©©©...©©..©©...©©©©.....©
6 ©....©©©.....©©..©©.....©©©....©
7 ©...©©©......©©..©©......©©©...©
0 ©..©©©.......©©..©©.......©©©..©
1 ©..©©........©©..©©........©©..©
2 ©.©©©............©©............©
3 ©.©©.............©©............©
4 ©.©©©©©©©©©©©©©..©©©©©©©©©©©©©.©
5 ©.©©©©©©©©©©©©©..©©©©©©©©©©©©©.©
6 ©............©©.............©©.©
7 ©............©©............©©©.©
0 ©..©©........©©..©©........©©..©
1 ©..©©©.......©©..©©.......©©©..©
2 ©...©©©......©©..©©......©©©...©
3 ©....©©©.....©©..©©.....©©©....©
4 ©.....©©©©...©©..©©...©©©©.....©
5 ©......©©©©©©©©..©©©©©©©©......©
6 ©........©©©©©©..©©©©©©........©
7 ©..........©©©©..©©©©..........©
0 ©..............................©
1 ©..©©©.©..©..©©..©...©.©..©©©©.©
2 ©.©....©..©.©..©.©©..©.©.©.....©
3 ©.©....©©©©.©©©©.©.©.©....©©©..©
4 ©.©....©..©.©..©.©..©©.......©.©
5 ©..©©©.©..©.©..©.©...©...©©©©..©
6 ©..............................©
7 ©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©
The Logo.

To be able to fill these data to the buffer with ease, then we can create an image data table. This technique is similar to how to show the variation of Running LED on exercise 5 of the Easy and Fun Learning Microcontroller book or on the LED Simulation article. Each image table has the same size with the size of the buffer. And for the case of the logo above, we need four 32 bytes size image tables.

Like on the Running LED exercise, the work of preparing the table is a tedious job and requires precision. But you should not be discouraged if you want to make the table of the large and complicated image because you can use the aid program ImgTable.exe. The program will help you to convert bmp format images into an image table that we can use it in the program using either the M51 format or using the SDCC format. So to get an image table, you simply create an image using MSPaint, and then do the conversion using ImgTable.exe.

ImgTable.exe can do the conversion from bmp file with a monochrome format up to 24 bits format. But because the table will be used to lit the LED which of course is equivalent to a monochrome format, the 24 bits format would be first converted by ImgTable.exe into the monochrome format. Therefore, it is better if you save the images you create with monochrome format to save on file size.

Rules applied by ImgTable is that the pixels that are black will be converted into 1, while the white pixels into 0. For colors other than black and white, then the three basic color elements will be summed first, then divided by three. After that, if the value is closer to the black will be interpreted as black, and if it is closer to white will be interpreted as white.

Table creation sequence is from left to right and from top to bottom. From top to bottom means every eight pixels will be taken as one byte. For example, an image with a size of 32 x 32, it will be four tables with the size of 32 bytes. The first table stores the data of the coordinates (0,0) to (31,7) by the rule that the upper left pixel is (0,0) and the lower right pixel is (31.31). The second table is (0,8) to (31,15). So forth.

In this example, all tables store the entire image data appropriately because the high of the image size is a multiples of eight. If the size of the image is not a multiples of eight, then the final table will have the remaining bits. For example if the image size is 32 (width) x 33 (height), then the number of tables are five tables with size of 32 bytes. And the last table only use bit 0. While bit 1 to bit 7 will be filled with 0.

Return to the LED matrix, we must display the four parts of the logo one by one. But if we display them alternately, then the shape of the logo will not be seen clearly. We will only see the incomplete images that appear alternately. Therefore we have to show by shifting it up or down. However, we have created tables that contains the data of the image blocks. So we can not retrieve data from the image coordinates (0,1) to (31,8) directly. For that, we need one more buffer with the same size as the first buffer. If we call the first buffer as the display buffer, then we call the second buffer as hidden buffer because it was not for displaying data to the LED matrix. This buffer is only used as an aid in manipulating the display data.

In case we want to shift the image up, then we can describe the arrangement as if the buffer is as follows:

01245...
abcde...
Numbers = the display buffer, alfabets = hidden buffer.

The first time, we fill the display buffer with data 0, so that all the LEDs will be turned off. Then we put the first image block table on hidden buffer. After that do a bit shifting between a and 0, b and 1, c and 2, and so on. Do these shifts of up to eight times, which means that all parts of the image block has been on display buffer. And before doing the ninth shift, we must place the second image block into the hidden buffer. And the next step is an iteration of the previous step.

For more details, you can see the program listing for the demo above that is written in the format of M51 and c. In the listing, there is DelayTime constants that you can replace to change the speed of picture motions.

To try on the simulator, then you must set the port link so that both Port0 and Port1 are linked to MXLED.exe by the message link with the WM_USER message, and lParam of Port0 is 2 and lParam of Port1 is 1. You also have to set the configuration of MXLED size as 8 x 32 landscape.

Happy trying and please do not hesitate to ask if there are less clear. Hopefully useful.