| Electronics > Beginners |
| Can I multiplex a 2-digit 7-segment display one segment at a time? |
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| Peabody:
--- Quote from: ogden on December 02, 2018, 09:36:43 am --- --- Quote from: Peabody on December 02, 2018, 05:27:02 am ---So in the full version, I'll have the seven segments of both digits directly connected to I/O pins, with no resistors, and the two common anode pins connected to I/O pins through 470 ohm resistors. That's a reduction from 9 resistors and 2 transistors to 2 resistors and no transistors. Not bad. --- End quote --- 7 resistors and 2 transistors are way cheaper than pins of microcontroller you literally waste. Also as already noted - if you really have enough pins to connect every segment, then don't multiplex. --- End quote --- I didn't say that clearly enough. I'm only using 7 pins for the segments. The respective segments of both digits are connected to the same pins. The digit is selected via the common cathod or anode. So I'm using a total of 9 pins to drive two digits. |
| Peabody:
--- Quote from: Peabody on December 02, 2018, 05:27:02 am --- If I get time tomorrow, I'll see what would happen if it were four digits multiplexed the same way, with each segment ON 2ms out of 56ms. --- End quote --- I did further testing and found that this doesnt work for three digits or four digits, at least at the 2ms ON time. Both produced substantial flicker. I also tested 1/16 in case the decimal point is needed, and found a hint of flicker there as well. So it appears that two digits of seven segments each (1 of14 segments at a time) is right at the edge of what works at 2ms ON time. |
| Nusa:
Flicker fusion sensitivity is going to vary among humans, so you may or may not be a good measure of the average human. Fatigue is a factor, so the well-rested are more sensitive. Metabolic rate is a factor, so the young are more sensitive. Rods are much more sensitive than cones, so peripheral vision is more sensitive. Also, flicker is easier to detect in brighter displays. I'd aim for 30 Hz as a minimum refresh rate. Higher would be better. |
| ogden:
--- Quote from: Peabody on December 02, 2018, 02:15:47 pm ---I didn't say that clearly enough. I'm only using 7 pins for the segments. The respective segments of both digits are connected to the same pins. The digit is selected via the common cathod or anode. So I'm using a total of 9 pins to drive two digits. --- End quote --- Well, then you need 2:7 multiplex scan, not 1:14. If this is too difficult task for you to code, then you shall reconsider your occupation [kidding] ;) |
| Peabody:
--- Quote from: ogden on December 02, 2018, 04:31:29 pm --- --- Quote from: Peabody on December 02, 2018, 02:15:47 pm ---I didn't say that clearly enough. I'm only using 7 pins for the segments. The respective segments of both digits are connected to the same pins. The digit is selected via the common cathod or anode. So I'm using a total of 9 pins to drive two digits. --- End quote --- Well, then you need 2:7 multiplex, not 1:14. If this is too difficult task for you to code, then you shall reconsider your occupation [kidding] ;) --- End quote --- I don't understand your comment. The whole point of this exercise was to see if I could multiplex one *SEGMENT* at a time, not one digit at a time. So I am NOT doing 2:7 multiplexing. Two digits have a total of 14 segments, and I'm cycling through them one at a time - the individual segments of the first digit followed by the individual segments of the second digit, one segment at a time. So every digit is turned on 1/14 of the total time. This isn't too difficult for me to code. And by the way, saying "kidding" doesn't make it any less insulting. |
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