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8*8 matrix LED grave with ATmega16


Properties

This describes a 8-by-8 LED matrix with the following properties:
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Hardware

The whole circuitry (LED matrix, processor part, current drivers, supply) is displayed in the schematic.

Schaltbild In the upper portion the wiring of the LEDs is shown. The eight cathodes of the upper and lower four lines are connected. The four anodes of a column are also connected, leading to eight upper and eight lower anode lines.

The cathode lines are each driven by a transistor BD439, because a maximum of up to 400 mA current can occur. For the anode lines transistor types BC547 are sufficient, because always only one LED is on. The driver transistors are necessary to stay within the current limits that a complete port can deliver.

The bases of the 24 driver transistors are connected to three processor ports via resistors. The processor has a 10-pole ISP interface for programming and a four pole DIL switch also connected.

The supply for the operating voltage of 5 V is unspecific. The regulator 7805 devellops some heat during operation, so it should be mounted to a small heat sink (approx. 20 K/W).


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Design

The parts are placed on two grid boards 10-by-10 cm (4-by-4 inches), that are placed back-by-back.

LED boardOn one board all LED are mounted.

Processor+SupplyAll other parts are mounted on the second board.

ISP+SwitchesThe ISP interface and the DIL switches are accessable from the side.

ConnectionThe two boards are interconnected with 12-pole connectors. These two connectors bring eight columns and four lines each to the other side.

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Software

The software is written in assembler and availabe here in HTML-Format and here in assembler text format. At the end of the source code individual text sequences can be configured.

Integrated in the source code is a ASCII code table. This table was designed with a spreadsheet. The sheet is availabe here in Open Office format resp. here in Excel format (as exported from OO format, no warranty for functionality and correctness).

When programming the processor the fuses have to be set according to the settings described in the source code file. Especially the JTAGEN fuse has to be cleared, otherwise three driver port pins in port C doesn't work correct.

The assembled flash code and the EEPROM content have to be programmed.

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