New light bar meter technology and its driving force

1. LED light column

As a novel indicating unit, LED light bars have been widely used in the international instrumentation industry. Compared with commonly used pointer-type instruments, they retain the intuitive characteristics of analog instruments while offering advantages such as rich colors, strong shock resistance, small size, and long lifespan, making them a preferred product for replacing mechanical moving-coil instruments. The combination of LED light bars and digital instruments has become an ideal display method in the current instrument display field, and therefore, it is receiving increasing attention and popularity.

1.1 General Structure and Applications of Light Pillars

A light bar, also known as a light bar, is a programmable analog bar graph formed by a series of light-emitting diode (LED) chips arranged in an equidistant array. It provides an intuitive display, is shockproof and anti-magnetic, operates at low voltage, consumes little power, is highly reliable, has no mechanical transmission parts, and eliminates reading errors.

LED light columns are generally used in the following applications:

● It can be used in conjunction with various sensors or transmitters to display measured physical quantities such as temperature, pressure, liquid level, voltage, current, frequency, speed and flow rate;

● The organic combination of analog and digital displays allows digital and analog quantities in industrial process control to be displayed on the same panel, providing both trend displays and precise digital values, making it a popular display method currently.

● Diverse display methods: Utilizing color variations in the light bar, it can reflect normal (green), warning (yellow), and alarm (red) states in industrial control processes. It can also visually display the corresponding liquid and gas phases within a container using red and green on a single light bar. Furthermore, it can utilize upper and lower limits at both ends and a dark band in the middle to indicate the safe working area on the same light bar. In addition, there are deviation displays reflecting the "positive and negative errors" of physical quantities, light bar color band displays replacing mechanical color band meters, and special light bars with angles of 90°, 120°, 180°, and 270°.

Currently, domestic companies such as Hangzhou Jingda Automation Instrument Co., Ltd., Hangzhou Xinxing Automation Instrument Factory, and Shenzhen Zhongzikong Instrument Co., Ltd. have produced a variety of bar graph display instrument devices.

1.2 Commonly Used Beam Structures and Pin Arrangements

LED light pillars are generally composed of multi-layer gold-plated printed circuit boards with LED chips, transparent gratings, and other components. In addition to using high-quality LED chips, processes such as high-pressure airflow impact, high and low temperature aging, and sealing and curing with high-molecular organic compounds are employed to reliably guarantee the quality of the light pillars.

A qualified light column, after being powered on, exhibits characteristics such as uniform brightness, consistent performance, clear display, and no missing or dark lines. Colors include red, green, yellow, and combinations of red and green, or green and red. The anode and cathode are connected in a matrix configuration. Depending on the driving requirements, the segment polarity can be either common cathode or common anode. Light columns driven by dedicated chips are of the common anode type.

Optical beams generally have many pins, such as 22 pins for a 101-line beam and 17 pins for a 51-line beam. They are available in models such as 101-line A, 101-line B, 101-line C (all 10×10) and 51-line A, 51-line B (all 10×5). Their pinouts are listed in Table 1.

1.3 Precautions for using LED light columns

Because light bars have many pins, disassembly after soldering is difficult. Therefore, testing and confirmation of satisfactory performance are necessary before soldering. Since there are currently no professional testing instruments, users can only judge by visual inspection. As long as the display is clear and the brightness is uniform when powered on, with no missing or dark lines, it is considered合格 (qualified). Users can also purchase a "Simple Light Bar Tester" (250 RMB/unit) produced by Hangzhou Sanke Industrial Co., Ltd. for testing, which is more convenient and simple to use. Strict control of soldering temperature and time is essential. Excessive temperature (>270℃) and excessive time (>3 seconds) will affect the conductivity between the light bar pins and the printed circuit board, leading to poor display.

The surface of the light column grating should be kept clean. If there is slight contamination, it can be gently wiped with a soft cloth dampened with water, but chemicals such as alcohol should not be used for cleaning.

The driving current of an LED chip must not exceed 20mA, otherwise it will shorten the chip's lifespan.

2. Dedicated driver chip for light beams, IC9504

There are many driving methods for LED light pillar products. Directly driving LED light pillar devices using the dedicated integrated circuit IC9504 has the characteristics of fast response speed, reliable performance, low power consumption, high precision, and good stability. It is suitable for mass production and is a relatively simple and economical choice.

IC9504 is a dedicated driver integrated circuit for LED light pillars manufactured by Hangzhou Sanke Industrial Co., Ltd. It adopts a 16-pin dual in-line package and common anode drive.

2.1 Features of IC9504

The IC9504 dedicated LED beam driver chip has the following characteristics:

●Simple power supply, single 5V power supply;

● Employs dynamic scanning display method, resulting in low power consumption (1mA/line);

● It adopts an output method that converts and displays the input analog signal simultaneously, requiring fewer external circuits. For standard 4-20mA or 1-5V input signals, the zero-adjustment potentiometer can be omitted, and only full-scale adjustment is needed;

● Employing CMOS technology, laser correction is used for resistor networks that affect accuracy, ensuring uniformity across all segments. There are no high-current drive components on-chip, resulting in minimal temperature rise. Therefore, it offers high stability, reliability, and precision.

●High driving current, capable of driving up to 8 101-line optical columns. Wide driving range, capable of driving 201-line optical columns, dual-color optical columns, or M×N matrix optical columns.

2.2 Pin Description

Figure 1 shows the pin diagram of the IC9504 dedicated chip. The functions of the main pins are as follows:

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VREF: Reference power input terminal, used to adjust the full-scale display of the input signal.

CLK: Pulse input terminal. The height of the light column can be adjusted by using the duty cycle of the clock pulse, that is, the ratio of the light column being on and off in one cycle.

P10: 10-segment stepped wave output terminal.

Q1～Q10: 10-segment control output terminals, typically connected to transistors to drive the light beams.

CTR: Mode adjustment control output. Connect to VDD (5V) for single-bar or multi-bar display. Connect to the analog switch integrated circuit control terminal for dual-color, deviation, or zone display.

VDD: Power supply terminal.

VSS: Power ground.

2.3 Precautions for using IC9504

The power supply voltage for IC9504 must not exceed 7.5VDC, otherwise the chip will be burned out. 5VDC is recommended.

A full-scale display is achieved by inputting 0.5V to 2.5VDC. All other signals must be converted to this range. An adjustable base TL431 can be used for adjustment around 2.5V.

The accuracy of the input analog resistors should be above 1%.

The brightness adjustment resistor should be selected according to the brightness of the LED light column, and should generally be between 0.5kΩ and 1.5kΩ.

The operational amplifier should be selected with an output to ground, such as the LM324 dual op-amp or the LM358 dual op-amp.

The analog ground and digital ground on a printed circuit board are only allowed to be connected at one point, and must be close to the power output, such as the output of a three-terminal regulator.

3. Practical application circuit of IC9504

Driving LED light pillars with IC9504 is very simple. The entire driving circuit consists of four circuits. The three-light pillar driving circuit with 101 lines × 2 + 51 lines × 1 requires no additional circuits except for adding the LM3914 line display driver. Similarly, when driving multiple light pillars, only the LM3914 driver needs to be added.

Figures 2 and 3 show the electrical schematics of the three-beam and single-beam displays, respectively.