Seven Segment Display

G

George Sephton

Senior Member
Hi,
Ive just got a clock 7-segment display from Vishay (http://www.vishay.com/docs/83180/83180.pdf), common cathode but I am confused. There is an A-G + DP Input and 4 cathodes for each display, plus 2 for colon and a 2nd dot but how does that show 4 seperate numbers? I really don't see how I can display 4 seperate numbers on it? I intend to connect a PICAXE 08M to a ICM7211 (4 digit seven segment display driver) but how does each number seperate itselfs?

Thanks for any help.
George.
 
E

eclectic

Moderator
@George

Just possibilties, but
1. Search Manual 3 for "4026"
2. Search the Forum for "Multiplex"

ps. Did you buy these, or obtain them as samples?
e
 
K

kevrus

New Member
at a quick glance, I would suggest that some multiplexing would be necessary to display four digits. POV, (persistence of vision) is the phenomenon that allows this to work.
 
B

BeanieBots

Moderator
It's a display for use with multiplexed signals.
Does your driver have multiplexed outputs?

EDIT:
Curiosity got the better of me. I looked up the ICM7211.
You CANNOT use that display with a ICM7211 for TWO reasons.
Firstly, the ICM7211 is for LCD displays. The one you have is LED.
Secondly, the ICM722 (for LEDs) does NOT have multiplexed outputs.

You COULD drive that display with a PICAXE with 8+4 outputs.
 
Last edited:
G

George Sephton

Senior Member
BeanieBots said:
You COULD drive that display with a PICAXE with 8+4 outputs.
Click to expand...
PICAXE 08M, not enough ports. Shift register springs to mind, and I have several 74HC164s How does a shift register actually work? Also how would I do that just send Digit (A-G) and Select (1-4) so quickly that the eye can't tell the difference?
 
B

BeanieBots

Moderator
You can't.
Using a shift register would be too slow.
There might some fancy way of pre-loading "a" shift register with the segment data and then using extra hardware to do the multiplex clocking but it's too late in the day for me to think about right now.

EDIT:
You could feed the eight bit data from your 164s into a tri-stateable octal latch. (74..374). Then use a free running 1 to 4 ring counter (clocked 4017 with OP4 fed back to reset) to enable the octal latch outputs onto the display whilst also using the ring counter to enable the display commons. Might need a few inverters here and there but that could all be done with correct use of whatever drive transistors you are going to use. Needs a little thought but doable with a handfull of chips.
 
Last edited:
W

westaust55

Moderator
George Sephton said:
Shift register springs to mind, and I have several 74HC164s How does a shift register actually work?
Click to expand...
George,

with all due respect, have you heard of datasheets?
Have you ever searched for one?

But to get you started in very simple terms:
a shift register such as the 74HC164 or 74HC595 comprise 8 D-type flip-flops (FF) (I sense another question coming on :rolleyes:).
Each bit of data is presented at the input pin and the clock pin pulsed to move all the bits of data along one FF.
After 8 clock pulses, 8 bits of data have been moved into the shift register.

In the case of the 74HC164 as each bit moves to a new position it is immediate seen at the outputs so the outputs are seen to ripple as the data moves through.

With a 74HC595, there are also separate latches so after the necessary (usually 8) bits have been shifted in the data is transferred to output latches with another (3rd) signal pulse. This means the output lines are stable until the required data is assembled in the shift register and avoids the ripple effect.
 
M

manuka

Senior Member
George- start by pondering "What is it you intend to do". Maybe just keen to use some 7 seg. LEDs? If so then try a 20M, as it can easily drive all/any segments directly when suitably programmed. Stan
 
G

George Sephton

Senior Member
I know what a flip flop is, lol. I will read the data sheet again but like I said it's just a 4 digit 7-segment display with one anode for each segment and 1 cathode per digit therefore the data would have to be sent with each digit so that each digit looks different while the gap of all other displays being blank is so short the human eye just sees 4 numbers. But the ICM7211 requires 4 sets of anodes not 1 set and 4 cathodes, but I will read. I have looked into all you have said and have multiplexers on their way: 4:16 so I can use 8 for each digit and 4 for the cathodes and just update and change each digit very fast. I thinks its the best way for it to work, HOWEVER I will read the datasheet again (page to page) to see if my problem can be solved...
 
B

BeanieBots

Moderator
Sounds like you knew the answer all along:rolleyes:
However, you've still missed the biggest issue.
Stop looking at the pinout. READ again. What is the difference between the 7211 and 7212?
What type of display do you have?

Let's start again.
Do you want a diplay (LCD) that can be used with a 7211 or a driver for that multiplexed LED display.
There absolutely NO WAY you can drive that LED display with a 7211. You will also have GREAT DIFFICULTY and need a lot of support chips to drive that LED display with a 7212.
 
hippy

hippy

Ex-Staff (retired)
@ George : It looks like you are trying to make two incompatible technologies work together.

Four digit 7-segment+DP displays come in two forms - Multiplexed, one drive line per segment and DP for all digits plus one drive line per digit; 12 signals in total. Non-Multiplexed, one drive line for each segment and DP of each digit plus one ( to four ) drive line per module; 29-33 signals in total.

Display drivers come in two forms as well to match the display, multiplexed and non-multiplexed. It is not easy ( and certainly not sensible ) to not use the right driver for the right display.

Your description of the display indicates it is multiplexed, the driver you are looking at is for a non-multiplexed display, and in addition the ICM7211 is for LCD not LED.
 
G

George Sephton

Senior Member
Aha, Like I said I have a multiplexer on its way and I'll try that but I have a few of these to make so I'll look into a 4-digit 7-segment MULTIPLEXED LED Display driver. Thanks for all the tips though. I did have the 7211 knocking around at first I didn't get it especially for this project I just wondered if it'd work, next time I'll read all of the datasheet,
Thanks to everyone for all the advice.
George.
 
You must log in or register to reply here.
Top