{"id":6862,"date":"2012-12-29T17:18:58","date_gmt":"2012-12-29T22:18:58","guid":{"rendered":"http:\/\/embedded-lab.com\/blog\/?p=6862"},"modified":"2016-10-27T22:06:27","modified_gmt":"2016-10-28T02:06:27","slug":"introducing-a-new-serial-spi-8-digit-seven-segment-led-display-module-using-max7219","status":"publish","type":"post","link":"https:\/\/embedded-lab.com\/blog\/introducing-a-new-serial-spi-8-digit-seven-segment-led-display-module-using-max7219\/","title":{"rendered":"Introducing a new serial (SPI) 8-digit seven segment LED display module using MAX7219"},"content":{"rendered":"

Seven segment LED displays are brighter, more attractive and provide a far viewing distance as well as a wider viewing angle as compared to LCD displays. The major drawback of using seven segment LEDs is they are resource-hungry. Time-division multiplexing is the most common technique of interfacing\u00a07-segment LEDs to microcontrollers. With this technique, an 8-digit seven segment LED display with the decimal point requires at list 16 I\/O pins of the microcontroller, which is quite a lot.\u00a0Consequently, their use with low pin-count microcontrollers (such as PIC12F series) is not practically feasible.\u00a0Here’s our latest version of the MAX7219 based serial seven segment LED display module (SPI7SEGDISP8.56<\/strong>)\u00a0that will allow you to add 8 digits of seven segment LED displays to your project using only 3 I\/O pins, and provides full control of all the digit segments including decimal points. You can even cascade two or more of these modules together without sacrificing any extra I\/O pin. SPI7SEGDISP8.56<\/strong> display kit\u00a0is also available for purchase on Tindie<\/a><\/strong> for $12.99.<\/p>\n

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SPI7SEGDISP8.56: 8-digit serial seven segment LED display<\/p><\/div>\n

<\/p>\n

Circuit diagram<\/strong><\/p>\n

The SPI7SEGDISP8.56<\/strong> display module is based on MAXIM’s MAX7219 display driver chip that provides a 3-wire serial (SPI) interface to drive 7-segment LED displays (common-cathode type) up to 8 digits.\u00a0Included on-chip are a BCD decoder, multiplex scan circuitry, segment and digit\u00a0drivers, and an 8\u00d78 static RAM to store the digit values. The segment current for all LEDs is set through an external resistor. However, the device is also capable of providing a software control of the display brightness (16 steps from minimum to maximum) through an internal pulse-width modulator. For more details on the internal block diagram and operation of MAX7219, read my earlier project Serial 4-digit LED display<\/a><\/strong> and the product datasheet<\/a><\/strong>.<\/p>\n

The circuit diagram of the\u00a0SPI7SEGDISP8.56<\/strong>\u00a0display\u00a0is pretty straightforward and follows the guidelines described in the datasheet. Two 4-digit CC LED displays (0.56″) are used in\u00a0SPI7SEGDISP8.56<\/strong>\u00a0to form a joint 8-digit display. JP1 header provides access to power supply, DIN, LOAD, and CLK signal lines. Similarly JP2 contains the same signal lines except DIN is replaced by DOUT pin. This allows easy cascading of multiple displays. For cascading, DOUT from one MAX7219 goes into DIN of another. C1 and C2 are decoupling capacitors and R1 set the maximum current value per segment. Read the\u00a0MAX7219 datasheet<\/a>\u00a0<\/strong>for more details on selecting the value of R1.<\/p>\n

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Circuit<\/p><\/div>\n

Interfacing examples<\/strong><\/p>\n

The SPI7SEGDISP8.56<\/strong> module can be interfaced with any microcontroller that has 3 I\/O pins available. If the microcontroller features a built-in hardware SPI, then the display module can be interfaced as a SPI slave device. In that case the SPI signal lines SDO (serial data out), SCLK (serial clock), and SS (slave select) from the microcontroller can be directly connected to the DIN, CLK, and LOAD pins of MAX7219. The LOAD signal is active low.<\/p>\n

In case the host microcontroller doesn\u2019t have a hardware SPI module, the interface can be implemented in software. In my previous project (Serial 4-digit LED display<\/a><\/strong>) I have described how to write a software SPI routine to drive the MAX7219 based LED display module using three general purpose I\/O pins of the PIC12F683 microcontroller. Same guidelines can be followed to write display routines for the SPI7SEGDISP8.56 module.<\/p>\n

SPI7SEGDISP8.56<\/strong> and Arduino<\/strong><\/p>\n

The\u00a0LedControl<\/a><\/strong>\u00a0library allows you to easily interface MAX7219-driven seven segment LED displays to Arduino. The library also supports cascading of multiple MAX7219 devices (maximum 8 devices). The following Arduino sketch is an example of interfacing one SPI7SEGDISP8.56<\/strong>\u00a0module. It displays numbers 1 through 8 on the eight 7-segment LED displays of SPI7SEGDISP8.56<\/strong>.<\/p>\n\n

#include "LedControl.h"<\/span>\n\/\/ Arduino Pin 7 to DIN, 6 to Clk, 5 to LOAD, no.of devices is 1<\/span>\nLedControl lc=<\/span>LedControl(<\/span>7<\/span>,<\/span>6<\/span>,<\/span>5<\/span>,<\/span>1<\/span>)<\/span>;<\/span>\nvoid<\/span> setup(<\/span>)<\/span>\n{<\/span>\n \/\/ Initialize the MAX7219 device<\/span>\n  lc.shutdown<\/span>(<\/span>0<\/span>,<\/span>false<\/span>)<\/span>;<\/span>   \/\/ Enable display<\/span>\n  lc.setIntensity<\/span>(<\/span>0<\/span>,<\/span>10<\/span>)<\/span>;<\/span>  \/\/ Set brightness level (0 is min, 15 is max)<\/span>\n  lc.clearDisplay<\/span>(<\/span>0<\/span>)<\/span>;<\/span>     \/\/ Clear display register<\/span>\n}<\/span>\nvoid<\/span> loop(<\/span>)<\/span>\n{<\/span>\n  for<\/span>(<\/span>int<\/span> i=<\/span>0<\/span>;<\/span> i&<\/span>lt;<\/span>8<\/span>;<\/span> i++<\/span>)<\/span>{<\/span>\n   lc.setDigit<\/span>(<\/span>0<\/span>,<\/span>i,<\/span>i+<\/span>1<\/span>,<\/span>false<\/span>)<\/span>;<\/span>\n  }<\/span>  \n  delay(<\/span>1000<\/span>)<\/span>;<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
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Interfacing the SPI LED display module with Arduino<\/p><\/div>\n
For cascading a second MAX7219 device, the DOUT pin of first device should be connected to DIN pin of other, and corresponding CLK and LOAD pins must be tied together. In SPI7SEGDISP8.56, DOUT pin is accessible through JP2 header. JP2 and JP1 header pins are compatible for direct cascading (see the picture below) by plugging them together.<\/p>\n
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Cascading two SPI7SEGDISP8.56 modules<\/p><\/div>\n
The following Arduino sketch illustrates daisy-chaining three\u00a0SPI7SEGDISP8.56 <\/strong>modules using the\u00a0LedControl<\/a><\/strong>\u00a0library.<\/p>\n\n
#include "LedControl.h"<\/span>\n\/\/ Pin 7 to Data In, 6 to Clk, 5 to LOAD, number of devices is 3<\/span>\nLedControl lc=<\/span>LedControl(<\/span>7<\/span>,<\/span>6<\/span>,<\/span>5<\/span>,<\/span>3<\/span>)<\/span>;<\/span>\nvoid<\/span> setup(<\/span>)<\/span>\n{<\/span>\n  \/\/ Initialize the 3 MAX7219 devices<\/span>\n  for<\/span>(<\/span>int<\/span> k=<\/span>0<\/span>;<\/span> k&<\/span>lt;<\/span>3<\/span>;<\/span> k++<\/span>)<\/span>{<\/span>\n    lc.shutdown<\/span>(<\/span>k,<\/span>false<\/span>)<\/span>;<\/span>  \/\/ Enable display<\/span>\n    lc.setIntensity<\/span>(<\/span>k,<\/span>15<\/span>)<\/span>;<\/span> \/\/ Set brightness level (0 is min, 15 is max)<\/span>\n    lc.clearDisplay<\/span>(<\/span>k)<\/span>;<\/span>    \/\/ Clear display register<\/span>\n  }<\/span>\n}<\/span>\nvoid<\/span> loop(<\/span>)<\/span>\n{<\/span>\n  int<\/span> count =<\/span> 0<\/span>;<\/span>\n  for<\/span>(<\/span>int<\/span> j=<\/span>0<\/span>;<\/span> j&<\/span>lt;<\/span>3<\/span>;<\/span> j++<\/span>)<\/span>{<\/span>\n    for<\/span>(<\/span>int<\/span> i=<\/span>0<\/span>;<\/span> i&<\/span>lt;<\/span>8<\/span>;<\/span> i++<\/span>)<\/span>{<\/span>\n     lc.setDigit<\/span>(<\/span>j,<\/span>7<\/span>-<\/span>i,<\/span>count,<\/span> true<\/span>)<\/span>;<\/span>  \/\/ Decimal point enabled<\/span>\n     count ++;<\/span>\n     if<\/span>(<\/span>count ==<\/span> 16<\/span>)<\/span> count=<\/span>0<\/span>;<\/span>\n    }<\/span>  \n    delay(<\/span>1000<\/span>)<\/span>;<\/span>\n  }<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
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Three SPI7SEGDISP8.56\u00a0modules in cascade configuration driven by 3 I\/O pins of Arduino<\/p><\/div>\n
SPI7SEGDISP8.56 display kit is available on Tindie<\/span><\/a><\/span> for $12.00.<\/strong><\/span><\/h3>\n
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SPI7SEGDISP8.56 display\u00a0kit for $12.00<\/p><\/div>\n
Soldering parts is pretty easy. The MAX7219 chip, resistor, and capacitors are soldered on the bottom side whereas the LED displays go to top side of PCB. The PCB size is approximately 4.8″ x 1.1″ (12.3cm x 2.8cm). Detail assembly instructions are available<\/span> here<\/a><\/strong>.<\/p>\n
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Top and Bottom views of SPI7SEGDISP8.56\u00a0PCB\u00a0<\/p><\/div>\n
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Assembled board top and bottom view<\/p><\/div>\n
Tindie buying links:<\/strong><\/p>\n
SPI7SEGDISP8.56 buying link – Red color<\/strong><\/a><\/p>\n
SPI7SEGDISP8.56 buying link – Yellow color<\/a><\/strong><\/p>\n
SPI7SEGDISP8.56 buying link – Green color<\/strong><\/a><\/p>\n
SPI7SEGDISP8.56 buying link – Blue color<\/strong><\/a><\/p>\n
Buyers from countries other than USA can also use following links for lower shipping cost<\/strong><\/p>\n
SPI7SEGDISP8.56 buying link – Red color<\/strong><\/a><\/p>\n
SPI7SEGDISP8.56 buying link – Yellow color<\/a><\/strong><\/p>\n
SPI7SEGDISP8.56 buying link – Blue color<\/strong><\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
Seven segment LED displays are brighter, more attractive and provide a far viewing distance as well as a wider viewing angle as compared to LCD displays. The major drawback of using seven segment LEDs is they are resource-hungry. Time-division multiplexing is the most common technique of interfacing\u00a07-segment LEDs to microcontrollers. With this technique, an 8-digit seven segment LED display with the decimal point requires at list 16 I\/O pins of the microcontroller, which is quite a lot.\u00a0Consequently, their use with low pin-count microcontrollers (such as PIC12F series) is not practically feasible.\u00a0Here’s our latest version of the MAX7219 based serial seven<\/p>\n","protected":false},"author":1,"featured_media":6863,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[245,437],"tags":[439,533,534],"class_list":["post-6862","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-embedded-lab-projects","category-products","tag-max7219","tag-serial-led-display","tag-spi-seven-segment-display"],"_links":{"self":[{"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/posts\/6862","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/comments?post=6862"}],"version-history":[{"count":35,"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/posts\/6862\/revisions"}],"predecessor-version":[{"id":12360,"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/posts\/6862\/revisions\/12360"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/media\/6863"}],"wp:attachment":[{"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/media?parent=6862"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/categories?post=6862"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/embedded-lab.com\/blog\/wp-json\/wp\/v2\/tags?post=6862"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}