7segmentdisplaybinary
I have a BCD input in the form of 8 wires (eight bit number, up to 511 decimal) and I want to display it on a seven segment display.
I have found a product which has 4 1/2 digits and a converter, but according to the datasheet, there are only 4 BCD inputs (four bit number, up to 31 decimal). Am I reading the datasheet wrong?
I have also heard about multiplexing but I do not understand it.
The datasheet can be found here.
The product can be found here.
Thanks,
What you need to do is convert the binary into something called BCD - Binary Coded Decimal.
Basically BCD is binary, but only takes the values 0-9 for each digit.
If you can still get hold of them (no idea if you can), there was a 7400 series IC that does the conversion. As I recall it was 74185.
Alternatively, if they are not available, you could use a parallel EEPROM IC or something like that. If you store the BCD equivalent values in addresses 0-15 of the EEPROM, then the lower 4 address bits become your 4bit binary input, then 5 of the bits of the data outputs can be your BCD value (the 5th bit being carry - i.e. 10).
Thinking about it, you could even use an 8-bit EEPROM to do the whole thing (including 7-segment). If you use the lower 7 bits for the first 7-segment, and the other data bit can go to segments B&C on the second 7-segment display. Again by storing the equivalent values in addresses 0-15 you can make a lookup table to generate the mapping.
2049...
The trick is one needs to get refreshing per digit out of your head and think about updating the whole display two "rows" at a time instead.
The layout of the segments is more dictated by the routability of them on the glass. Unlike PCBs, vias are not available so crossovers can't happen.
Best Answer
You found a pretty nice display, it includes the BCD and to 7 segment for you; that way you can control the segments with four lines, not including the multiplexing.
I can't hold your hand using this, I'll give some input though.
You have a simplified diagram of how the display works here in the datasheet:
So the main signal pins that you have to use are A through E with L to I.
Like Alex said, you need to activate each transistor (A to E) one at a time, to turn on a single digit. Activate A to show Digit 5, activate C to show digit 2.
L through I controls what number is displayed on the digit that is activated. So if you want '5' on digit 2, set C HIGH and write "0101" to JKLI respectively.
The datasheet is nice enough to provide a reference:
So the idea is to turn on one of the digits for a short period of time, and display the number you want on that digit. Then cycle through the rest and set the correct binary value for the respective digit.
If you want "1234" displayed: activate A and drive "0100", activate E and drive "0011", activate D and drive "0010", activate C and drive "0001". The idea is you cycle through the 4 digits so fast that a user cannot tell they are being blinked. Which is called multiplexing.
Ok, that's a lot more help than I was planning on giving but I needed a quick break from work. Good luck.