# What is the use of this 2-digit 7 segment display

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?

• You need to multiplex between pin 5 and 10. Commented Jan 25, 2017 at 10:27
• 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? Commented Jan 25, 2017 at 11:04
• Your eyes make it persistent. This is how almost every display work, TVs and the like. Commented Jan 25, 2017 at 11:17
• 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)..
– user16324
Commented Jan 25, 2017 at 11:17
• 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? Commented Jan 25, 2017 at 11:28

## 1 Answer

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.

• 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? Commented Jan 25, 2017 at 11:01
• @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... Commented Jan 25, 2017 at 11:05
• 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 ? Commented Jan 25, 2017 at 11:07
• 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. Commented Jan 25, 2017 at 12:35
• Also called Flicker Fusion Threshold Commented Jan 25, 2017 at 17:11