Quick Question

K

kollinsb

Member
This is probably a very stupid question but I'll ask it anyway. I have a couple of each of these 7-Segment Displays:

http://www.futurlec.com/LED/7DR8021AS.shtml
http://www.futurlec.com/LED/7FR3641AS.shtml

I can make them display numbers fine but how in the $%$%^$%&^ do I make them display DIFFERENT numbers? I can make it display 44 or 4444 all day long but if I want it to display 12 or 1234 how would I wire the hardware? I'm going off the interface manual and using either the 4026 or 4511 with a 14M or an 08M (don't have a 20M or I'd go direct) I must be missing something? Any nudge in the right direction?

These are common cathode by the way...

Thank you!
 
L

lanternfish

Senior Member
From what you are describing you have commoned the a - g segments as is normal pra ctice but have also commoned the cathodes (to 0V). This means both displays will always be on. You need to switch each display cathode on via a transistor (or 2003/2803) driver.

Or use the circuit described on page 22 of the third PICAXE manual.

Cheers
 
S

SilentScreamer

Senior Member
The basic idea is that you can use pins to be high or low and use a pin to turn each segment on or off. You then flash between each digit very quickly.

You connect every pin to an output. You then make the digit that you want to light's anode high the each segment that you want to display you make low. You then go to the next digit by making every anode low except the one you want to use. For example:

The second link (4 digits).

Pin 12 = high
Pin 9, 8 and 6 = low
Pin 1, 10, 7 and 4 = low
Pin 2, 3, 5 and 11 = high

That displays a 4 on the first digit. If you then display different digits on each display and keep looping around each digit so your mind thinks that they are always on, when they are in fact flashing.
 
Last edited:
You must log in or register to reply here.
Top