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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? I segment can be driven independently, f you think the picture above is big, they can display the numerals 0-9 and it’s about half the size of the real many letters. There’s also a matching McCoy. That’s all we could fit (large!) decimal point alongside each across the pages of SILICON CHIP! digit containg five LEDs in series. This LED display, which can be Placed alongside each other, the expanded to up to 10 digits, uses display is striking – especially at night. special LED “light bars”, each about Five digits (the number presented 70mm x 15mm, each of which contain here) are some 600mm in width. When two rows of six 200-300mCd LEDs in we checked how far away we could series. The ends of the light bars are clearly read them, we gave up at 100m. angled so that when placed into the familiar 7-segment display pattern, they form ultra-large digits, ES each a whopping 150mm (6 FEATUR m 7-segment display rge 150m La • s inches) high. to display higher value Easily add extra digits • And unlike some multi2 x opto-isolated inputs LED displays we’ve seen, • • 1 x 10-bit 0-5V input they don’t cost upwards of a ut • 1 x 10-bit 0-20mA inp ial thousand dollars. ser L TT ial, • RS485 ser ters Each digit has its own pre- • RS232 serial or USB with optional conver assembled PC board. As each • 12VDC powered 70  Silicon Chip 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 siliconchip.com.au OPERATING MODES Design by Greg Radion (Ocean Controls Pty Ltd) Article by Greg Radion and Ross Tester 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. The hardware Various PC boards add together to achieve the above functions. We’ve already mentioned the giant LED display siliconchip.com.au • 0-5V scaled • 0-20mA or 4-20mA scaled • Up/Down counter wit h reset and preset • Quadrature up/down counter • Tachometer RPM • Frequency • Up/Down second tim ers • ASCII or Modbus ser ial over RS485 or TTL boards. A KTA-255 Large 7-Segment Controller PC board is mounted to the back of the first digit. This board includes a microcontroller, constant current LED driver, shift register and all circuitry needed to connect the various input signals. The microcontroller reads in the input signals and scales them according to the user settings and then sends out the data to the shift register, which controls the data displayed on the 7-segment digit. Of course, you’re usually going to need more than one digit and this is where the smaller KTA-256 Large 7-Segment Driver PC boards come in to play. This has a constant-current LED driver, shift register and IDC header connections for connection to the previous and next digits. One of these is mounted on the back of each additional digit. The circuit Fig.1 shows the circuit diagram of the KTA-255 module and Fig.2 the KTA-256. As you can see, Fig.2 is basically a cut-down version of Fig.1. There are some labelling shortcuts on the PC board – these are shown in green on the circuit diagram. On the K-255 PC board an AVR ATMega168 microcontroller controls operations. Two of the analog inputs have been connected to the VI and CI terminals, with 10k inline resistors to provide some protection for the chip. The CI input also has a pair of resistors totalling 250which will generate 5V reference for a 20mA signal passed through them. December 2009  71 rameters can be loaded to default at power up, by making a connection between MI and COM on K3 on the side of the PC board. This can be done with a bare wire, or by temporarily soldering a wire in place. Let’s take a look at the operating modes in more detail. 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. A pair of opto-couplers isolate the digital input signals I1 and I2, and a DS3695 (MAX485 equivalent) converts RS485 levels to 5V TTL serial. The output to the LED segments is delivered via a TLC5916 IC. This is a constant current LED driver/shift register from Texas Instruments. The operation of the TLC5916 is much like a 74HC595 shift register in that it has a shift in data pin, a clock pin, a latch pin and a shift data out pin. However, the outputs on the TLC5916 will regulate their current according to one programming resistor. The AVR controls the data stream to the TLC5916. The output of the TLC5916 is connected to the input pin of the next board using headers, conveniently labelled IN and OUT. Configuration The KTA-255 configuration soft- ware sets up the display mode and parameters. User-configured parameters include: • Operating mode • Number of the digit to display the decimal point on • Scaling values • Count-by values • Reset values • Display delay time (to reduce flicker) • Debounce time (so that switch presses do not make multiple counts) • Modbus address • Baud rate • Parity Not all parameters are relevant to each operating mode. The configuration software will hide the parameters which are not used. To ensure that the configuration software can communicate with the controller, the communications pa- Analog 0-5V: The Analog 0-5V input mode will take a 0-5V signal in via the VI and COM terminals and scale it according to the values used in set up. The allowable range is -32,768 to +32,767 and decimal places can be used as well. For example, to use as a 0-5V voltmeter and assuming 5 digits to measure to four decimal places (0.0000 to 5.0000) the operating mode is set to 0-5V with the following parameters: Decimal Place = 5 (Show the decimal point on digit 5), 0V Value = 0, 5V Value = 5. That is all that is required but if the display flickers too much, the display delay time can be increased. If faster changes need to be seen on the display then the delay time can be decreased. Analog 0-20mA: The Analog 0-20mA input is between terminals C1 and COM, which includes a 250 load resistance. It can be easily used with 4-20mA sensors as the software allows either a 0mA or 4mA value to be entered and the other value is automatically calculated. Most industrial sensors will use a 4-20mA signal – a good example is a temperature sensor with 0-100°C output over 4-20mA. Assuming five digits The “business side” of the large panel meter. The first display PC board (ZJCXKD) has attached the first-digit driver PC board (and in this case an RS232 interface). Subsequent displays have the slave driver PC boards, all of which are daisychained with IDC cable. The display PC boards are pre-assembled; other PC boards are available in kit or assembled forms. 72  Silicon Chip siliconchip.com.au siliconchip.com.au December 2009  73 TB5 TB4 4.7k COM 2 1 5 4 6 3 2 MOSI SCLK RST GND SC RT COM 2 1 2 1  100nF AN2 120 130 2x 10k 4 5 4 OPTO2 4N25  * GREEN LABELS REFER TO MARKINGS ON PC BOARD AN1 5 2 100nF 4.7k 20 GND 22 8 XTAL2 XTAL1 PD6 PD7 PB0 PD4 PB2 PB1 PC5/ADC5 PC4/ADC4 PC3/ADC3 GND PC1/ADC1 PC0/ADC0 PC6/RST PB5/SCK PB3/MOSI Aref PC2/ADC2 AVcc IC2 ATMEGA168 PB4/MISO PD2 PD3 Tx RxEN Rx 7 Vcc 10 9 22pF X1 20MHz A 16 Vdd d g a a O0 LE CLK K 1 GND OE Rext SDO O7 O5 O6 O4 O1 SDI f dp e c 100nF K A D1 1N4004 IN GND 13 15 14 12 11 10 9 7 5 3 1 OUT 7805 3 2 1 4 3 6 2 1 5 (TO SLAVE DIGITS) LATCH CLK GND GND 910 SDO Vcc TB1 CON1 +V Vcc GND +V 152mm 7-SEGMENT DISPLAY (YSD-1100AR7B-15) bg IN 10 IC1 TLC5916 9 +V GND OUT REG1 7805 O2 O3 e f D1–D3 4 LATCH 12 3 CLK 13 2 5 6 7 8 SDI 22pF 100nF d c b dp Vcc 12 14 16 18 100nF 14 6 16 15 28 27 26 25 21 100nF CONTROLLER/FIRST DIGIT MODULE 100nF 24 23 1 19 17 18 4 5 3 Tx 11 4.7k COM GND DI 4 OPTO1 4N25 2 Rx DE 3 RE 2 RO 1 MAX485 RX TX Vcc LARGE 7-SEGMENT PANEL METER COM GND CI VI MISO MI MO A K A K 5 GND 8 Vcc 1 OPTIONAL USB/RS232 3 INPUT 4 Fig.1: the first digit requires this controller to drive it. This is shown opposite attached to the left-most display board. 2009 SC  1 TB3 Vcc D3 1N4004 1k D2 1N4004 5V I1- I1+ I2- I2+ 1k 7 B DI– D– GND 6 A DI+ IC3 D+ CON3 2 ANALOG INPUT 3 DIGITAL INPUT I1 1 DIGITAL INPUT I2 2 1 1 RS485 2 INPUT 3 TB2 4.7k 100nF 5V CON4 Vcc = +5V CON2 5 CON3 +V +V 9 18 16 14 12 1 a f b c 152mm 7-SEGMENT DISPLAY 10 dp e g a bg c d d 5 f dp e 1 3 5 7 100nF Vcc Vcc 1 16 8 7 6 5 2 SDI 2 3 4 O3 Vdd O4 O2 O5 O1 O6 O0 IC1 TLC5916 O7 SDI SDO CLK Rext LE GND OE 9 10 11 12 SDO 14 15 3 4 910 GND GND CLK CLK LATCH SC LARGE 2009 LATCH 7-SEGMENT PANEL METER again, we can display to two decimal places giving a range of 0.00 to 100.00. The operating mode is set to 0-20mA with the 20mA value to 100 and the 4mA value set to 0 (this will automatically set the 0mA value to -25). The decimal point position can be set to 3 (or 4 for more accuracy, albeit at the cost of never actually being able to display 100.000). Counter: In counter mode, an optically isolated signal on inputs I1+ and I1- will add the “count-by” value to the display each time it is triggered. To count down, a negative value can be used in the count-by value. The count-by value can be from -32,768 to +32,767 (signed 16-bit) but the displayed values (count total) can be from -2,147,483,648 to +2,147,483,647 (signed 32-bit). Obviously more than 5 digits would be needed to display these values. The I2+ and I2- terminals are used for another optically isolated signal, this is used to reset the counter to the “reset to” value 74  Silicon Chip 2 13 1 6 Fig.2: the circuit diagram of the slave digit controller – essentially a “cut-down” version of the first digit controller overleaf. 6 3 4 SLAVE DIGIT MODULE When a connection is made from VI to COM the display will subtract the “count by” value from the currently displayed value. Up/Down Counter: The Up/Down Counter mode is very similar to the Counter mode, however in this mode the optically isolated signal on I2+ and I2- subtracts the “countby” value and the non-isolated signal on VI and COM resets the display. Quadrature: In Quadrature mode a quadrature encoder can be used to count up and down. Phase A should be connected to I1+ and I1-, while Phase B should be connected to I2+ and I2-. The nonisolated input VI will reset the counter value. It should be noted that each encoder edge is used for a count signal, giving four times the line resolution of the encoder, ie, a 1000 line encoder will give 4000 counts per revolution. Tachometer: A tachometer pulse signal is fed into I1+ and I1-. If more than one pulse is given per revolution then the number of pulses per revolution can be entered into the “division” parameter. Frequency: The Frequency mode is much the same as the Tachometer mode, except that the signal is not converted to RPM before being displayed. Maximum measured frequency is approximately 20KHz. Up Timer: In Up Timer mode the unit will display hours minutes and seconds, with a decimal point to separate each. The I1+ and I1- input starts the timer, the I2+ and I2- input resets the timer to zero and the VI input pauses the timer. The timer will count upwards each second until the value set in the configuration is reached; if the set value is zero the counter will keep counting up. Down Timer: Similar to Up Timer mode, the Down Timer mode counts seconds, however, this time it is downwards. The reset value is set by the configuration software and the timer stops counting at zero. ASCII: For easy connection to computer programs and microcontrollers an ASCII mode has been added. Once the display has been put into ASCII mode and the baud rate and parity have been set in the configuration software, a link must be placed between VI and COM to make the device interpret the incoming data as ASCII, not setup instructions. There are always eight data bits and there is one stop bit. TTL serial from microcontrollers and RS485 serial can be sent directly to the controller. For RS232 or USB, an RS232 to TTL converter or USB-TTL serial converter is needed. Both of these are available from Ocean Controls. To d i s p l a y numbers, send 128 them to the dis(a) 64(f) play, followed (b) 2 by a Carriage R e t u r n c h a r32 acter (a value (g) of 13 or 0x0D). (c) 4 16 (e) For example, (d) (dp) “-1.234<CR>” 8 1 sent to the dissiliconchip.com.au 100nF IN 910 TLC5916 K2 K3 OUT IC1 K1 Double-sided boards – only bottom layer shown Note how the 2nd, 4th, 6th, 8th, 11th, 13th, 15th and 17th header pins are cut off to prevent them shorting to the copper tracks underneath. In the diagram each segment is labelled with a decimal value. To turn on a particular pattern of segments, add their values together and send that value after the special character. For example, to turn on the top four segments and display a square the value for each of those segments is added together (128 + 2 + 32 + 64 = 226.) This is shown on the display by sending the value 17 followed by the value 226. The K-255 and K-256 boards, shown here attached to the back of their display boards, with Figs. 3 and 4, the component overlays, between them. The PC board at the top of the left photo is an optional RS-232 serial interface. play will show “-1.234” on the display. The space character (32 or 0x20) will leave a blank space. The DEL character (127 or 0x7F) will clear the display. Letters can also be shown on the display, sending any of the characters a-z (97-122 or 0x61-0x7A) will show that character. As with all 7-segment displays, some characters will not show correctly and some can be mistaken (eg, “D” and “O”) but most are intelligible, especially in context. If special characters need to be displayed, then the special character DC1 (17 or 0x11) is sent. The character following this is used to turn on each of the individual segments of the 7-segment display. Holding Register Modbus The display controller can also be used as a Modbus slave. Modbus is an industrial protocol supported by many PLC’s and SCADA packages. It consists of 16-bit holding registers and input registers, as well as 1-bit coils and status bits. Only holding registers are implemented in the KTA-255 Display Controller. Further information on the Modbus protocol can be found at www.modbus.org. If the controller has been put in Function 1 Value to display low 16-bits 2 Value to display high 16-bits 3 Decimal point position 4 Mode 0 = Modbus, 1 = 0-5V, 2 = 0-20mA, 3 = counter, 4 = U/D counter, 5 = quadrature, 6 =tacho, 7 = frequency, 8 = ASCII, 9 = up timer, 10 = down timer, 11 = Modbus 5 Low scale, count by value, pulses/rev (depending on mode) 6 High scale, reset value (depending on mode) 7 Display delay time 8 Debounce time 9 Modbus address 1 to 243 10 Baud 0 = 9600, 1 = 2400, 2 = 4800, 3 = 9600, 4 = 19200, 5 = 38400, 6 = 57600, 7 = 115200 11 Parity 0 = none, 1 = odd, 2 = even siliconchip.com.au December 2009  75 Parts List KTA-255 1st Digit Driver 1 PC board labelled KTA-255v1, 77 x 52mm 1 28-pin IC socket 1 8-pin IC socket 2 6-pin IC sockets 1 TO-220 heatsink 3 3-way 3.5mm terminal blocks 2 2-way 3.5mm terminal blocks 1 2x3-way header pin set 1 18-way header pins, 90° 3 6mm M3 screws 1 M3 nut 2 5mm M3 Nylon spacers 1 6-way (or 10-way) 15cm IDC connector cable Semiconductors 1 TLC5916 IC (IC1) 1 ATMega168 Microcontroller, preprogrammed (IC2) 1 DS3695/MAX485/LTC485 IC (IC3) 2 4N25/4N35 Opto-Coupler (IC4, 5) 1 7805 5V regulator (VREG1) 3 1N4004 diodes (D1-D3) 1 20MHz crystal Capacitors 8 100nF monolithic (C1-C7, C9) 2 22pF ceramic (C10, C11) Resistors 2 10k 2 4.7k 1 910 1 130 4 1k 1 120 KTA-256 Slave Digit Driver 1 PC board labelled KTA-256v1, 52x 25mm 2 2x3-way header pin sets 1 18-way header pins, 90° 2 6mm M3 screws 2 5mm M3 Nylon spacers 1 6-way (or 10-way) 15cm IDC connector cable Semiconductors 1 TLC5916 IC Capacitors and resistors 1 100nF monolithic 1 910 Suggested display hardware (n = number of digits) 1 Acrylic sheet, red, 6mm thick 200mm x (25 + 115n)mm (Alternatively for a higher contrast display 3mm red and 3mm grey can be sandwiched together.) 3n 12mm Nylon spacers 3n 25mm M3 screws 3n M3 nuts 76  Silicon Chip Modbus mode and the slave address, baud rate and parity are set via the configuration software, the controller will then be ready to use on a RS485 Modbus network or via direct connection on RS232, USB or TTL Serial. To display values the first three holding registers are used. Holding registers 1 and 2 are combined together to give a 32-bit signed value from -2,147,483,648 to +2,147,483,647, holding register 1 holds the lower 16-bits, holding register 2 holds the upper 16-bits. Holding register 3 sets the decimal point position. To show “-98765.4321” on the display, holding register 1 would be set to 38735, holding register 2 would be set to 50465 - respectively the lower and upper 16-bits of the signed 32-bit number. These can be easily derived in the controlling application. Holding register 3 would be set to 5 to display the decimal point on the fifth digit. Modbus Registers: As well as being able to display values directly from Modbus, the holding registers also hold all the settings for the controller, in fact, the configuration software uses the Modbus protocol to set up the controller. In all except ASCII mode the current displayed value can be read via the first 3 holding registers. Assembly Both the KTA-255 and KTA-256 modules are available either as a kit of parts to assemble yourself or a fully built and tested module. As previously mentioned, the individual “digit” PC boards are only available pre-assembled. If you choose the kits (which are cheaper) assembly of the PC boards is quite straightforward. Each board is double-sided, through-plated soldermasked and silk screened and has been through electrical testing. This means that it should be free from defects but it is worth going over just to be sure. The lowest components – resistors and diodes – should be placed first and then the others mounted, generally in order of height. Make sure you take a look at the diagrams and pictures to see where the components are placed and in particular, how the connector K2 (KTA-255 or K1 on the KTA-256) is mounted underneath the board, making the connection to the back of the 7-segment display, as well as the 7805 voltage regulator with heatsink, bent 90° over the edge of the board. Once the PC board is fully assembled, check your work for solder bridges, dry joints, etc. If it looks OK then you can proceed to the next step, mounting the PC board to the back of the display, Attaching the PC boards The assembled KTA-255 or KTA256 PC boards are mounted on the back of the 7-segment “digit” display PC boards, positioned so that some of the pins can be soldered to the tracks underneath. While this may be enough to hold the smaller (256) boards in place, for added stability the top ends of all the boards are screwed to very short (5mm) Nylon spacers, glued to the back of the display board. Eight of the pins on connector K2 (K1 on KTA-256) are not needed – in fact, may short to tracks on the display PC board, so must be cut off before mounting. Make sure you do not cut off the wrong pins though. Take a look at the photo and you will see that the two centre pins are soldered in place, then every second pin is removed from the centre outwards, leaving 10 pins in total. Apply a couple of blobs of glue to hold the nylon spacers in place. A two-part epoxy glue is recommended. Hot melt glue is not recommended as the close-by 7805 regulator can produce quite a bit of heat, which could soften the glue. If a metal bolt is used on the 7805 and heatsink, ensure that it cannot short-circuit to the 7-segment display PC board – we used a small square of electrical tape where it touches the board. The main controller board and driver boards can now be connected together by using 6 or 10 pin IDC connector cables, taking note of the pin 1 index, denoted by the small arrow on the PC board. Testing The easiest way to test the display is to connect a 10k potentiometer to the 5V, V1 and common terminals of the main controller board (255) with the wiper to the V1 terminal. Apply power – the LED displays should come on with a random reading. Varying the pot over its travel should make the LED siliconchip.com.au one tinted grey and the other tinted red which gives a nice dark background but allows the digits to be clearly read. Acrylic sheet is normally available, cut to your specified size, from plastics dealers. Configuration software The software to drive it all is available free of charge from the Ocean Controls website (see address below). This should give you virtually all the control you need to configure the giant display to read whatever you want it to. An example of a configuration screen, setting up an analog voltmeter, is shown at left. Operation is quite selfexplanatory. Where to get it The KTA-255 and KTA-256 have been designed by Ocean Controls Pty Ltd, who retain the copyright. As previously mentioned, both kits and pre-assembled modules are available, which include PC boards, components and a programmed microcontroller (for 255s). Each comes with the LED board, but not the mounting plastic (except for the 5 digit assembled kit which comes mounted on Acrylic). Prices are as follows (all plus GST): The KTA-255 Configuration Software. The Windows software makes setting up the display very easy. The top radio buttons set the mode, at the bottom the relevant parameters will be enabled and non-relevant parameters are disabled. On the right the maximum and minimum values and the decimal place position are shown for the number of digits you have. Once the parameters are to your liking enter the COM port number the device is attached to and click “Write To Controller”, success or failure will be shown in the status box. Parameters from the display can be read out of the display device by clicking “Read From Controller” Cat No Description Kit Assembled KIT-255 Controller Digit (inc one display) $69 $89 KIT-256 Slave Digit (inc one display) $39 $49 KI5-255 5 Digit Kit (inc five displays) $203 KT5-255 5 Digit Unit (Assembled on Acrylic) $349 Nothing extra is required for use with RS485; however for programming with either RS232 or USB serial ports you will need: COV-201 ARD-011 reading vary between 0 and 100.00. RS232-TTL Serial Converter USB-TTL Serial Converter - $14.95 $21.50 For more information: Final mounting Ocean Controls, 3/24 Wise Ave Seaford VIC 3198. Ph (03) 9782 5882 www.oceancontrols.com.au How you mount the displays is really up to you and your particular application. We have attached them to two sheets of 3mm Acrylic, SC 27 47.5 67.5 47.5 67.5 47.5 67.5 47.5 67.5 45.5 200 67.5 46.5 600 115 115 189.5 18.5 27.5 115 71.5 65.5 Scaled drilling detail (don’t use same size!) to suit a five-digit display. Either a 6mm red or a 3mm red plus 3mm grey sheet of acrylic work very nicely. You may prefer to mount differently to avoid screws coming through the acrylic panel. siliconchip.com.au December 2009  77