How To Drive A 64 Led Matrix Show Utilizing 16 Control Strains

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Driving an individual LED is a straightforward task and all you do is connect the LED through a present limiting resistor to a management line. When the management line goes high the LED lights up and when the management line goes low the LED is off. The issue is that for those who try and drive an eight by eight matrix on this method you want sixty four particular person control strains and this is able to require a number of circuitry.

The way round it is to cheat and make use of a property of your eye called persistence of vision.

Persistence of Vision

Your eye actually remembers what it has seen for a very short time i.e. The picture in your eye persists for a short while. Tv designers made use of this truth a few years in the past (and nonetheless do in the present day) since the image created on a TV set consists of a single electron gun (actually three since there may be one gun for every shade).

Observe: LCD TVs work in a special way.

The electron gun scans over the complete TV screen at an extremely high rate. It really works by using electrical fields to alter the route of the stream of electrons (these electric fields are extraordinarily excessive voltage which is why it is vital by no means to open up a TV). The stream of electrons is deflected so that each row is scanned one line at a time. At each pixel the gun is turned on make the display screen phosphor mild up.

As long as the complete screen is refreshed earlier than your eye forgets the picture it seems to be to you just like the display screen has a relentless regular picture. If the refresh fee was decreased then you definately would begin to see the image flickering.

The rate at which the display screen needs to refresh is 50Hz i.e. 20ms and that is the speed needed in case you do multiplexing.

Multiplexing

To use persistence of imaginative and prescient in digital designs you make use of a technique referred to as multiplexing and it merely means sharing. As a substitute of driving every LED individually you can share a management line between a number of LEDs.

You only need to turn on a management line for a short time so long as you remember to repeat the output before the 20ms time limit.

Controlling the eight by 8 LED matrix

An led dot matrix show is solely an array of LEDs organized in a square grid. Each column is linked to 1 side of the led and every row is related to the other.

The matrix is arranged specifically for multiplexing and you may truly get away with eight column drivers and 8 row drivers so as a substitute of sixty four control traces you now solely need sixteen control strains i.e. A saving of seventy five%.

Word: This dialogue is for the common cathode LED matrix i.e. The place the cathode (-ve) of each column of LEDs is linked together. The type of matrix determines whether or not you drive a row high or low to turn on an LED.

To activate an individual LED in the matrix requires that you drive a row with a high voltage and permit present to circulate by the cathode. You usually allow present to move by attaching a transistor to a column connection and it’s turned on and off utilizing a control signal.

Once you activate the column transistor driving any of the eight rows will gentle up one of the eight row LEDs. To regulate the next column you flip off the 1st column transistor and turn on the following column transistor (out of the eight out there). Utilizing the identical row drivers you can now management this next set of eight LEDs.

In case you repeat this process making certain that each one columns and rows are pushed over the period of 20ms then it should look as if the show is not flickering in any respect i.e. It should appear that the LEDs are constantly driven.

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