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Ginormous 7-Segment LED Panel Meter Display

Have you ever had the need for a digital display that can be read from across the room? How about across the factory? How about fifty or even a hundred metres away?

Design by Greg Radion (Ocean Controls Pty Ltd)
Article by Greg Radion and Ross Tester

FEATURES

• Large 150mm 7-segment display

• Easily add extra digits to display higher values

• 2 x opto-isolated inputs

• 1 x 10-bit 0-5V input

• 1 x 10-bit 0-20mA input

• RS485 serial, TTL serial

• RS232 serial or USB with optional converters

• 12VDC powered

OPERATING MODES

• 0-5V scaled

• 0-20mA or 4-20mA scaled

• Up/Down counter with reset and preset

• Quadrature up/down counter

• Tachometer RPM

• Frequency

• Up/Down second timers

• ASCII or Modbus serial over RS485 or TTL

If you think the picture above is big, it’s about half the size of the real McCoy. That’s all we could fit across the pages of SILICON CHIP!

This LED display, which can be expanded to up to 10 digits, uses special LED “light bars”, each about 70mm x 15mm, each of which contain two rows of six 200-300mCd LEDs in series. The ends of the light bars are angled so that when placed into the familiar 7-segment display pattern, they form ultra-large digits, each a whopping 150mm (6 inches) high.

And unlike some multi-LED displays we’ve seen, they don’t cost upwards of a thousand dollars.

Each digit has its own pre-assembled PC board. As each segment can be driven independently, they can display the numerals 0-9 and many letters. There’s also a matching (large!) decimal point alongside each digit containg five LEDs in series.

Placed alongside each other, the display is striking – especially at night. Five digits (the number presented here) are some 600mm in width. When we checked how far away we could clearly read them, we gave up at 100m. Like all LED displays, during the day visibility depends to a large degree on ambient light – for example, it’s not as good in direct sunlight. Even so, it’s pretty impressive.

OK, so that’s the LED displays. But what do they display?

For maximum flexibility the display has been designed to accept multiple input signals. Parameters are set using a computer and saved to memory.

Input signal types are divided into 3 categories, analog, digital and serial.

Analog: Analog input modes include 0-5V DC and 0-20mA (industrial standard 4-20mA sensors can also be easily used). As well as voltage and current, these can be configured and scaled to display virtually any analog reading, such as temperature, humidity, pressure etc.

Digital: Digital input modes include counter modes (quadrature or up and down with reset and preset), tachometer (RPM), frequency and up or down timers.

Serial: Serial input modes include RS485, TTL and (with an optional converter) RS232 or USB with the option of ASCII display or Modbus RTU controlled display. Various baud rates are supported. The device parameters are also set up using the RS485 / RS232 / USB connection to a computer with provided software or Modbus enabled device.

Click for larger image
Click for larger image
Each of the seven segments is made up of a 70 x 15mm LED “lightbar” as shown above. The PC board which carries them measures 112 x 165mm.

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