7-channel SDU on LEDs. Scheme, description

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7-channel SDU on LEDs. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Musician

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The scheme of the proposed device resembles the scheme from [1] but has a different functional purpose. LEDs with a diameter of 5 mm in red color can change the brightness of the glow together or independently in 7 channels. In the absence of these LEDs, you can use others, because. the function of limiting the current through the LEDs (approximately at the level of 20 mA) is successfully performed by the internal buffers of the AT89C2051 microcontroller.

(click to enlarge)

The circuit is operable at a supply voltage of 6 V and can be powered by four AA galvanic cells without reducing the brightness of the LEDs during the discharge of galvanic cells. The microcontroller (MK) DD2 in this device is in a state of sequential reading of memory cells with cyclic repetition (along the ring). For programming, you do not need to know the MK command system. The program consists only of codes that are sequentially issued from memory to the pins of port P1.

With each clock pulse from the generator on the DD1 chip, the MK outputs codes from the memory (2048 cells) byte by byte to the pins of the P1 port, to which the LEDs are connected. The logical "1" of the code is a high level at the corresponding output of the MK, at which the pair of LEDs connected to it is extinguished. When "0" - the output is low, and a pair of LEDs is on. The change in brightness is regulated by a variable resistor R3.

To ensure that the transition from one memory cell to another has a minimum duration and does not affect the glow of the LEDs, the generator pulses have a large duty cycle. The MC memory is divided into 16 parts of 16 blocks. Each block is divided into frames of 8 cells that simulate pulse width modulation (PWM) to change the brightness of the LEDs. The "0" state on each port pin in the frame is 8 memory cells in a row for the maximum brightness, and one of 8 cells for the minimum brightness. Therefore, it turns out 8 gradations of brightness. 16 blocks provide its rise and fall, and 16 parts allow you to independently change the brightness of any channel (or any other combination that depends only on the developer's imagination).

For programming MK, you can use the simplest programmer without electronic components [2]. As the simplest example of changing the brightness of all LEDs, you need to memorize the code. given in the table, and repeat this block to the end of the entire memory 15 more times.

The device can be used as part of more complex light-dynamic installations on MK to reduce the amount of their software.

Literature

V. Melnik. Souvenir Christmas tree on a microcontroller... without a program. - Radio. 2004, No. 11. P.36.
V. Melnik. AT89C2051 programmer for IBM PC. - Radio world. 2006, No. 4, p.20.

Author: V.Melnik, Dneprodzerzhinsk, Ukraine

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