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I just came across this weird device while searching for a 2-Digit 7 segment display with an inbuilt BCD decoder. This is because I am using an MSP430G2553 with limited number of GPIOs with few ADCs & GPIOs used for other purpose & I want to keep the footprint as minimal as possible by avoiding separate BCD decoder IC.

Following are my questions,

  1. In which scenario will this particular 2-digit 7 segment display be useful? Both digits would be displaying identical numbers!!. http://www.taydaelectronics.com/datasheets/A-756.pdf

  2. Are there any 2-digit 7 segment displays with inbuilt BCD decoder?

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    \$\begingroup\$ You need to multiplex between pin 5 and 10. \$\endgroup\$ – winny Jan 25 '17 at 10:27
  • \$\begingroup\$ But would the Digit be persistent? i.e if pin 5 is disconnected during multiplex from ground would Digit 2 continue to show the current number it is set to? \$\endgroup\$ – Duster2503 Jan 25 '17 at 11:04
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    \$\begingroup\$ Your eyes make it persistent. This is how almost every display work, TVs and the like. \$\endgroup\$ – winny Jan 25 '17 at 11:17
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    \$\begingroup\$ There is no persistence in the LEDs. The persistence you need is in your eyes - so you need to display both digits with the appropriate anode enabled, more than 60 times a second (usually several hundred).. \$\endgroup\$ – Brian Drummond Jan 25 '17 at 11:17
  • \$\begingroup\$ Thanks for confirming this, I am aware of motion picture's principle, but was not sure that this 7-segment display expects the same principle to be used. So this device expects to be driven at frequency > ~20Hz for each 7-segment leading to write cycles of >40Hz to keep both digits visible to human right? \$\endgroup\$ – Duster2503 Jan 25 '17 at 11:28
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To answer your first question: The two digits will only be displaying the same number if both pin 5 and 10 are active at the same time.
If you toggle between them then you can display two different digits.

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  • \$\begingroup\$ But in any case, only one digit would be active right? if pin 5 is not active then the Digit 2 would be off. In simple words, is it possible for me to display number 12 with this unit? \$\endgroup\$ – Duster2503 Jan 25 '17 at 11:01
  • \$\begingroup\$ @Duster2503 if you need to display two characters such as "Hl" or "E2" etc. then you can use both 5 and 10. When you activate 10, you will drive ABCDEFG to display 'E'. When you activate 5 you will drive ABCDEFG to drive '2'. then you are time multiplexing... \$\endgroup\$ – User323693 Jan 25 '17 at 11:05
  • \$\begingroup\$ understood, but when I deactivate pin 10 , would the digit 1 continue to display 'E' ? how is it made persistent with it's cathode being floating ? \$\endgroup\$ – Duster2503 Jan 25 '17 at 11:07
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    \$\begingroup\$ If you switch between them at around 100 Hz or faster then it will look like they are both on. This is a fairly standard trick when driving LEDs. \$\endgroup\$ – Andrew Jan 25 '17 at 12:35
  • \$\begingroup\$ Also called Flicker Fusion Threshold \$\endgroup\$ – neonzeon Jan 25 '17 at 17:11

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