7 SEGMENT 2-3-4 DIGIT DISPLAY DRIVER - Page 1
Forum section: electronics / beginners

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 24, 2016, 08:13:04 pm
content: Hello i got into a project where i need to drive a 2-3 and 4 digit led displays.I originally designed it using 1 digit Seven segment displays being driven by CD4513 ics but i would need 17 of them for my total 17 digits.So i searched on how to multiplex 7 segment displays and found nothing (only arduino tutorials)I need a way to drive multiple digit displays using a clock and an ic but i dont know what ic to use.Thank you in advance.

author: alank2
author_rank: Super Contributor
timestamp: January 24, 2016, 08:17:51 pm
content: Too bad it isn't 16 digits. The max7219 can handle 8 at a time.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 24, 2016, 08:22:27 pm
content: I forgot to mention what displays i am going to be using.1X4 Digits1X3 Digits5X2 DigitsAlso the inputs wont be from a microcontroller but from 9 74HC390 ICsI attached the link from the schematic so you can see what i need exactly i am sorry for the poor quality.http://postimg.org/image/b1a2avjy3/

author: andre_teprom
author_rank: Regular Contributor
timestamp: January 24, 2016, 09:03:07 pm
content: The ULN2003 is able to drive a considerable current, and has a compact size.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 24, 2016, 10:03:12 pm
content: Ill search about it and create a schematic to test it thank you

author: rdl
author_rank: Super Contributor
timestamp: January 24, 2016, 11:56:48 pm
content: I never knew there was a 4013 until now.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 25, 2016, 12:17:20 am
content: I cant use the ULN2003 for the project because it need to be driven by a microcontroller from the schematics that i saw

author: rdl
author_rank: Super Contributor
timestamp: January 25, 2016, 12:25:13 am
content: No micro controller needed, it's just a transistor array.Quote from: ChrisGreece52 on January 25, 2016, 12:17:20 am

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 25, 2016, 01:07:46 am
content: oh ok thank you ill search more then try to figure out a schematic that works and come back to checkThank you

author: TerminalJack505
author_rank: Super Contributor
timestamp: January 25, 2016, 04:08:04 am
content: It looks like the real complication is that you have 17x4 (68) BCD input signals. If you drive the displays 1 digit at a time that will require 17 digit select signals + 7 segment signals. So it sounds like you need a device with about 100 pins.The only devices that I can think of off the top of my head that cannearlymanage the task are CPLDs and FPGAs. (They won't be able to handle the current coming through the digit's common cathode.)The (now obsolete) Xilinx XC9500-series CPLDs and some transistor array ICs (like the already-mentioned ULN2003) could do the job. The XC9500s are 5V parts that come in fairly high pin count packages and support high current (24 mA) outputs.You might have to resort to getting the parts from ebay or similar sources if you go that route, however, since they have been discontinued. Then, of course, there is the issue of programming them. Which is to say that you'll need a programmer (about $50.) So you might keep looking for other options and use a CPLD as a last resort.If it were me I'd probable split the task up between 4 XC9536 parts in 44-pin PLCC packages or 2 XC9572 parts in 84-pin PLCC packages. These are surface mount parts but are very easy to solder. So far as driving each of the common cathodes goes, the ULN2003 would work. You'd need three of them in this case.

author: SL4P
author_rank: Super Contributor
timestamp: January 25, 2016, 04:53:58 am
content: What about multiplexing the individual displays - not just the digits.So - all the first digit of all displays are paralleled, all the second digits, the 3rd, 4th etc... then time switch the whole display (common cathodes/anodes) so that only one display is driven for eaxh cycle, then the next display etc. through all seven displays.It will slow down the digit multiplexing, but there aren't so many digits - thus speed really isn't a problem.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 25, 2016, 01:08:53 pm
content: Quote from: SL4P on January 25, 2016, 04:53:58 amThat was about what i was thinking the undevided frequency will be 4.096 Mhz.After it is divided the 2 frequencies coming out will be 1Khz ( there will be a millisecond display) and 1.024 Hz for the led's i am planing to install between the Hours and minutes and seconds and minutes that will pulse every second.I can use another pin (2^9) to divide the 4.096 MHz signal to 8Khz so i can drive the multiplexing circuit.But i dont know how ...I dont want to involve an FPGA because it would rise the complexity level a lot. Also i need it to be simple and working.I could construct it only using and FPGA but i want it to be done with just CMOS logic.Thank you .

author: SL4P
author_rank: Super Contributor
timestamp: January 25, 2016, 01:17:48 pm
content: My discrete logic skills dropped off about 20 years ago, but what you want is pretty straightforward with a micro - but I respect that you're trying to go with cold hard chips.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 25, 2016, 01:21:28 pm
content: Quote from: SL4P on January 25, 2016, 01:17:48 pmThank you for that.If i wanted to go with a micro the project would be already completed i would need just the micro and some displays.Also i don't trust arduino running long term without resetting...but i really love the idea of something like a clock built by chips only