Light-dynamic device Traveling wave. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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Abstract. Light-dynamic devices (SDU) with programmable algorithms make it possible to create a wide variety of light-dynamic effects and control a large number of light elements according to the program. LEDs with linear (smooth) brightness control, unlike LEDs with discrete brightness control, require the use of a separate hardware PWM controller for each channel. Therefore, the complexity of such a device increases in proportion to the number of light elements.

This article discusses a 16-channel version of the SDU with smooth brightness control, which combines the simplicity of circuit solutions and software-implemented emulation of 16 hardware PWM controllers.

Overview. Simultaneous synchronous control of the brightness of a large number of light elements according to a linear law requires not only the use of a separate hardware PWM controller for each channel, but also synchronization of the operation of such controllers with a certain phase shift between channels. The proposed device is based on the architecture of a programmable 16-channel controller with a serial interface, discussed in [1]. The differences are in the reading algorithm and firmware of the EEPROM IC, as well as the use of more complex output registers such as 74AC595. This register consists of 16 trigger cells, the first eight of which are part of the buffer register, and the remaining eight are part of the output.

The use of a serial interface allows increasing the number of light elements with minimal hardware costs without significantly complicating the circuitry of the main controller, as well as simultaneously and synchronously controlling several sets of light elements via serial interface lines, the length of which can reach 100 m. In the simplest case, the SDU implements two lighting effects "traveling wave" type with a PWM sequence word length of 16 bits. Effects are changed automatically after four repetitions or are selected manually by pressing a button. With an increase in the amount of memory used by the EEPROM IC, it is possible to increase the number of channels, the number of effects, as well as the word length of the PWM sequence.

For smooth brightness control, this device uses the principle of Pulse Width Modulation (PWM). PWM is a way to encode a digital signal by changing the duration (width) of rectangular carrier frequency pulses. On fig. 1 shows typical PWM waveforms. Since, with pulse-width modulation, the pulse frequency, and hence the period (T), remain unchanged, then with a decrease in the pulse duration (t), the pause between pulses increases (diagram "B" in Fig. 1) and, conversely, with an increase in the duration the pulse pause decreases (plot "B" in Fig. 1). In our case, turning on the LED corresponds to the appearance of a logic zero level at the output of the register, so the brightness increases with increasing pulse duty cycle (plot "B" in Fig. 1), and, conversely, the brightness decreases with decreasing duty cycle (plot "C" in Fig. 1 ). Recall that the pulse duty cycle is the ratio of the pulse repetition period to their duration. The duty cycle is a dimensionless quantity and has no units of measurement, but can be expressed as a percentage.

This device uses a 16-bit word length of the PWM sequence, which corresponds to 16 gradations of brightness of the light elements. Such a number of gradations of brightness is quite enough for a visually smooth change in brightness with a period of rise and fall of the "traveling wave" not exceeding one second. With an increase in the period of brightness change to two or three seconds, the transitions between brightness levels (gradations) become visually noticeable, which will require an increase in the word length of the PWM sequence. But for most applications, if very slow reproduction of the effect is not required, 16 gradations of brightness are quite enough.

To control a remote set of light elements, three signal lines of the serial interface are used: "Data", "Clk1" and "Clk2". The first line "Data" is an information signal, and the other two lines - "Clk1" and "Clk2" are the strobe signals of the buffer and output registers, respectively, that are part of the IC 74AC595.

When operating on long uncoordinated communication lines, data transmission problems arise due to the well-known signal reflections and crosstalk induced by adjacent conductors included in the same bundle. Such reflections and interferences that occur in the light-dynamic system mean a violation of the aesthetic effect. This imposes restrictions on the length of the connecting line and imposes strict requirements on the noise immunity of a system using a serial interface.

The noise immunity of such a system depends on many factors: the frequency and shape of the pulses of the transmitted signal, the time between changes in the levels (duty cycle) of the pulses, the specific capacitance of the line conductors included in the bundle, the equivalent line resistance, as well as the input impedance of the signal receivers and the output impedance of the drivers.

The effects of long mismatched lines begin to appear when the signal propagation delay times along the line and back begin to exceed the duration of the rise and fall fronts of the signal. Any mismatch between the equivalent line impedance and the input impedance of the logic gate on the receiving side of the line or the output impedance of the driver on the transmit side will cause the signal to be reflected multiple times. The typical rise and fall times for the KR1554 series microcircuits are less than 5 ns, so the effects of long mismatched lines begin to appear when its length is only fifty to sixty centimeters.

Knowing the characteristics of the transmission line, such as total input capacitance and specific capacitance per unit length, it is possible to calculate the signal propagation delay time along the entire length of the line. A typical propagation delay time is typically 5-10 ns/m. If the length of the connecting line is long enough and the duration of the rise and fall edges of the signal is small enough, the mismatch between the equivalent line resistance and the input resistance of the CMOS logic element at the receiving side creates a signal reflection, the amplitude of which depends on the instantaneous value of the voltage applied to the input of the element, and the reflection coefficient, which, in turn, depends on the equivalent line resistance and the input resistance of the input gate.

Since the input impedance of the KR1554 series IC elements is many times greater than the equivalent resistance of a line made of a twisted pair or a shielded conductor, the reflected voltage at the receiver input doubles. This reflected signal propagates along the line back to the transmitter, where it is reflected again, and the process is repeated until the signal is completely attenuated.

We especially emphasize that reflections are in no way related to the frequency of the transmitted signal pulses, but are caused only by the high steepness of the fronts of the transmitted clock pulses. To combat reflections in professional circuitry, when working on a long line (100 m or more), special drivers are used that reduce the steepness of the fronts of the transmitted clock pulses, and thereby eliminate data transmission errors.

For operation on a line of relatively short length (from 10 to 100 m), standard logic ICs of the KR1554 series (74ACxx) are quite suitable. Due to their high load capacity, a capacitive load can be directly controlled. Balanced (symmetrical) current-voltage output (transfer) characteristics of the elements of these microcircuits make it possible to obtain almost the same rise and fall front times. In addition, powerful buffer elements based on Schmitt triggers with hysteresis, the minimum value of which is about 0,9 V at a supply voltage of 4,5 V, can be used to transmit signals to the line and receive, which creates an additional margin of noise immunity.

To compensate for the reflected signal in this device, so-called integrators or integrating RC chains are used. The need for them arises only when working on a line longer than 10 m in conditions of an increased level of interference. In the author's version of the device on lines up to 10 m long, the capacitors shown in the diagrams of the output registers by dashed lines were not used. The communication line with a length of up to 10 m is carried out by a bundle of 5 conductors, including "Power "+12V"" and "Common wire". In this case, no failures are observed, even without integrating capacitors. With a signal line length of 10 to 100 m, crosstalk induced by adjacent conductors increases. In this case, each signal line: "Data", "Clk1" and "Clk2" must be made with a separate twisted pair, and capacitors shown in the diagram by dashed lines should be installed on the output register boards. In this case, the remote registers and garlands are powered from a separate "+12V" power supply.

(click to enlarge)

Schematic diagram. The light dynamic device (Fig. 2) consists of the main controller board and two remote register boards, which are connected to the main board using three serial interface lines. A common conductor (not shown in the diagram) is also part of the connecting line and is made with a stranded wire with a cross section of at least 1 mm2. The connecting line ends with a 9-pin DB-9 plug. The printed circuit board has a mating connector XN1 (also not shown in the diagram).

The main controller board contains: a reset circuit on the Schmitt trigger DD1.4 and elements C3-R6-R7; master generator on the elements DD1.1 ... DD1.3; synchronization pulse generation circuit DD6.1, DD4.2…DD4.4, DD7.1, DD7.2; address counter DD6.2 multiplexer sampling DD9 and counters DD2.2, DD3.2, DD5.1, DD5.2 addressing IC EEPROM DD8; an LED bar for indicating the memory page number (HL1…HL4, green), an indicator for increasing/decreasing brightness (HL5, yellow), and an indicator for the number of the light-dynamic effect (HL6, red). Registers DD11, DD12 and LED line HL7…HL22 are installed on the main board to monitor the device performance. Powerful buffer elements based on Schmitt triggers of the KR1554TL2 (74AC14) type were used as drivers for signal translation. As a memory IC, you can use not only the EEPROM of the AT28C16 type, but also the RPZU of the KR573RF2 (RF5) type.

To develop a control program, a controller with an integrated programmer, considered in [2] and [3], was used. It is also possible to write an alternative control firmware using the "Virtual Programmer" ("Light Effects Dumper"), but, in this case, it is necessary to reassign the address lines of the EEPROM (EPROM) IC when programming it using a standard programmer. This feature is supported by all professional level industrial programmers and most intermediate level programmers. The need to reassign the address lines when programming the EEPROM is due to the fact that when developing the programmer discussed in [2] and [3], a different (reverse) order of the address lines was initially chosen for the convenience of tracing the printed circuit board. For a specific controller [2] and [3], the reassignment of address lines does not affect the operation in any way, since the data is read in the same sequence in which it was written. During the development of the “traveling wave” CDS, the numbering order of the address lines was preserved to ensure compatibility of this device with the programmer [2] and [3].

But the table shows a variant of the lighting dynamic effects firmware, generated using the program "Virtual Programmer" ("Light Effects Dumper"), so that readers can view the firmware using the program "Virtual Simulator" ("Light Effects Reader"), available at the link [4 ], and get better acquainted with the principles of operation of the device and the development of a control program.

Principle of operation. When the power is turned on, the integrating circuit C3-R6, together with the Schmitt trigger DD1.4, generates a short positive pulse that resets the counters DD2.1 ... DD6.2 (except for DD3.1, which is not used), and, thereby, resets the controller to its original state. The pulses of the master oscillator DD1.1 ... DD1.3 with a frequency of about 130 kHz (more precisely 131072 Hz) synchronize the counter DD6.1, followed by DD6.2 and the rest of the address counters. Looking ahead, let's say that one full cycle of increase-decrease in the brightness of the "traveling wave" in duration equal to two seconds corresponds to the frequency of the master oscillator exactly 131072 Hz. This value is derived from an output register update rate of 128 Hz, which is far superior to the ergonomic value of 85 Hz. Such a data update rate is necessary to eliminate the flickering of light elements and create the illusion of a smooth change in brightness.

(click to enlarge)

The timing diagram for the formation of synchronization pulses is shown in Fig.3. It can be seen from it that for each synchronization pulse of the output registers ("Clk2"), which is formed at the output of the DD7.2 element (pin 6), there are 16 synchronization pulses of the buffer registers ("Clk1"), which are part of the IC 74AC595. Moreover, the positive edge of the sync pulse (“Clk1”), which is formed at the output of the element DD4.3 (pin 6), falls in the middle of the familiarity of the data bit transmission. Synchronization of the buffer register at the moments falling in the middle of the familiarity, as established by experience, according to the results of tests of the basic version of the controller [1], corresponds to the maximum noise immunity when working on uncoordinated lines of great length. At the same time, there is no need to use integrators at the inputs of remote registers.

The very first negative pulse, counting from the moment the power is turned on, formed at the output of the DD4.3 element (pin 6), with its trailing edge (positive drop) writes the data bit read from the first cell of the EEPROM at the zero (0000h) address into the first triggers buffer registers that are part of the IC DD11 and DD14 with a simultaneous shift of information in the direction of increasing bits. The content of the output registers included in the IC DD11, DD12, DD14, DD16 does not change, and the LED strips display the current light-dynamic combination. As noted above, the word length of the PWM sequence is 16 bits, therefore, to display one level (gradation) of brightness on a line of 16 LEDs, it is necessary to transfer a data packet of 16 x 16 = 256 bits of information to the registers, which conditionally corresponds to one page of the address EEPROM space. Thus, a complete fade-in cycle takes 32 pages of address space or 8K, of which the first 16 pages (4K) are a half-cycle of brightness-up, and the second half, also 16 pages (also 4K in size) is a half-cycle of brightness decrease, counting relative to the first channel.

The negative edge of each positive pulse from output 2 (pin 4) of the counter DD6.1 increases the state of the counter DD6.2 by one, and, therefore, connects to the output of the multiplexer DD9 its decimal input, corresponding to the binary equivalent of the code, which, in turn, is connected to the output of the corresponding bit data IC EEPROM DD8. After writing 16 bits of data into the buffer registers of the IC DD11, DD12, DD14, DD16, the trailing edge (positive edge) of the negative pulse generated at the output of the DD7.2 element, the contents of the buffer registers of the IC DD11, DD12, DD14, DD16 are overwritten in their respective output registers. At the same time, a new combination is fixed on the LED lines HL7 ... HL22 and HL23 ... HL38. But the total (integral) brightness value corresponds exactly to sixteen 16-bit packets, i.e. 16 x 16 = 256 bits of data transferred to the registers over the serial lines as noted above.

Changing the levels (gradations) of brightness is indicated by a line of LEDs HL1 ... HL4, which displays the state of the counter DD3.2 in a binary code. As can be seen from the electrical circuit (Fig. 2), counting pulses come to the DD3.2 input from the DD2.2 output after dividing by eight using the DD2.1 counter. Such a frequency division of the output pulses DD2.2 is necessary for a slower increase in brightness than could be obtained without frequency division using the counter DD2.1.

Counters DD3.2 and DD5.1 ​​address the first half of the space IC EEPROM DD8 in the zero state of the counter DD5.2 and the second half of the address space IC EEPROM DD8 in the single state of this counter. Lighting effects selection mode - manual or automatic - is set by switch SA1. In the position shown in the diagram, the effects are automatically alternating after four repetitions. This is achieved by supplying counting pulses from the output of the third digit DD5.1 ​​(pin 5) to the input of the counter DD5.2. In the lower, according to the scheme, position of the switch SA1, short positive pulses are received at the input of the counter DD5.2 when the SB1 button is pressed. Status counters DD5.1 ​​and DD5.2 indicate, respectively, yellow (HL5) and red (HL6) LEDs.

Construction and details. The main controller is assembled on a printed circuit board made of double-sided fiberglass with dimensions of 140 x 90 mm and a thickness of 1,5 mm (Fig. 4), and the output registers (Fig. 5) are 90 x 30 mm (Fig. 6). The device uses fixed resistors of the MLT-0,125 type, tuning resistors - SP3-38b, non-polar capacitors (C1 ... C3, C8 ... C10, C12 ... C14) of the K10-17 type, oxide (C4 ... C7, C11, C15) - K50-35 or imported. Super-bright LEDs with a diameter of 3 mm (HL1…HL6) and a diameter of 5 mm (HL7…HL22) are installed on the main controller board, and super-bright LEDs of four colors KIPM-15 with a diameter of 10 mm are placed in an alternating sequence in a remote garland.

Given the difference in voltage drop across forward biased LEDs (for red and yellow this value is 2,1 V, and for blue and green - 3,0 V), it is necessary to connect the corresponding limiting resistors in series with the LEDs: 220 and 150 Ohm. To control a powerful load, the output registers must be supplemented with transistor or triac switches. It is possible to use directly on-site EEPROM type AT28C16-15PI memory chip type RPZU type KR573RF2 or KR573RF5 without changing the printed circuit board design.

Counters type KR1564 IE23 (74HC 4520N) can be replaced by K561 IE10 (CD4520AN), except for ICs DD3, DD5, to the outputs of which indicator LEDs are connected. Multiplexer DD9 type KR1564 KP7 (74HC 151) will replace KR1564 KP15 (74HC 251). The connecting line with a length of up to 10 m is made with a bundle of 4 stranded conductors with a cross section of 0,35 mm2 (for signal lines) and 1 mm2 (“common” wire) in isolation, and with a length of 10 to 100 m, the signal lines must be made in separate twisted pairs , and on the boards of the output registers, install integrating capacitors with a capacity of not more than 150 pF.

Preparation for operation of the device assembled from serviceable parts and without errors consists in writing the firmware to the EEPROM IC (EPROM) using a standard programmer. In this case, it is necessary to programmatically reassign the order of the EEPROM IC address lines by selecting the appropriate option in the program. Before programming the EEPROM chip, the text file of the program (see table) must be converted to binary format using one of the free converter programs, for example, [5]. You can select the desired playback speed for dynamic lighting effects using the trimmer resistor R3 on the main controller board.

Sources of

1. Odinets A. L. "Programmable 16-channel SDU and virtual simulator." - "Electrician", 2008, No. 4, p. 72-75, No. 5, p. 76-79.
2. Odinets A. L. "Autonomous 32-channel programmable light-dynamic device with a serial interface." - "Radioamator", 2005, No. 6, p. 20-23., No. 7, p. 22-23.
3. Odinets A. L. "Autonomous 32-channel programmable light-dynamic device with a serial interface." (Upgraded version.) - "Electrician", 2008, No. 11-12, p. 76-79., 2009, No. 1-2, p. 44-48.
4. dynamic-lights.narod.ru/LightEffectsReader.rar
5. winhex.com

Author: Odinets A.L.

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