The MAX7219, respectively the improved version MAX7221, from Maxim can control up to 64 LEDs or 8 seven-segment-displays (with common cathode). Therefore this circuit has 8 segment and 8 digit drivers for multiplexing the LEDs. The segment current is adjustable via an external resistor and it is also possible to adjust the brightness digitally. Display data is transmitted to the circuit via a serial 3-wire-interface at which several circuits can be cascaded. A decoding mode can also be enabled for comfortable controlling of seven-segment-displays. A datasheet can be downloaded from Maxim's homepage. The MAX7219 or MAX7221 is also used for the LED moving font, which can be found on the projects site.
The SAA1064 from Philips is programmable via I²C-Bus. One circuit can drive up to 32 LEDs multiplexed or 16 LEDs non-multiplexed. The segment current is adjustable in four steps. Up to four SAA1064 can be connected to the I²C-Bus. A datasheet is available on the homepage of Philips.
The ICM7218 from Maxim can drive up to 8 seven-segment-displays. There are four versions (ICM7218A,B,C and D) of this circuit. Displays with common anode need the ICM7218A or C while displays with common cathode need the ICM7218B or D. The circuits ICM7218A and B can also operate in a no-decode-mode which means that the segments can be driven independent from each other. So you can also connect up to 64 seperate LEDs but then you have to note that the segments for the decimal points are driven inverted. The datasheet can be downloaded from Maxim's homepage.
The MC14499 from Motorola can drive up to four seven-segment-displays with common anode. Display data is clocked in serially into the circuit: each 4 bits represent the BCD code of a digit and 4 bits are used for the decimal points. Into the output lines a-h current limiting resistors must be inserted and the cathodes of the displays must be connected to the MC14499 via driver transistors. A datasheet is available here.
A four digit LED-Display (seven segments display) which can be programmed via a serial RS232
interface is concerned. The LED segments are controlled by the I²C LED driver circuit SAA1064.
The I²C-Bus is provided from a microcontroller AT89C2051 via software. Display data is sent
via the serial RS232 interface to the microcontroller. There are four programming modes:
Binary mode: The display segments are determined by four bytes which are transmitted as
eight hexadecimal nibbles. Herewith any segment combinations can be displayed.
Hexadecimal mode: Four hexadecimal figures can be displayed, including some special
characters like decimal point or minus.
Decimal mode: Four decimal figures can be displayed, including some special
characters like decimal point or minus.
Besides there are commands for display test and clear display.
Furthermore the brightness of the LED-Display can be adjusted in eight steps.
The schematic and the software can be downloaded here:
Project files for hardware and software in ZIP format:
Serially controlled LED-Display V1.0
For the hardware the freeware version of Eagle 3.55 is required. It is available for free from CadSoft.
Schematic in GIF format:
Schematic of serially controlled LED-Display
Programmed microcontroller:
If you are interested in a programmed microcontroller, please send an
email including the project name.
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