Converting to hex from 7-seg out

[varunme]

How can i generate hex decimal values from a 7 segment out and so that i can process in a microcontroller or send to pc ?
(I have an instrument with hex out and no pc interfacing option, so i am doing it)

 

[embeddedlover]

U mean to ask 7-segment display? If so, 7-segment is a simple LED array.. u can only drive it..
Can you give your block diagram to understand more?

 

[BradtheRad]

1. Easy method...

Read the 7 wires as a unique hex value. As given in the table below:
Found at:
https://en.wikipedia.org/wiki/Seven-segment_display

Write a routine to take a hex value in column 3, and return the decimal value in column 1.

2. Difficult method using discrete IC's

Construct a decoder, made from 'AND' gates, and 'NAND', and 'OR', and 'NOR', etc.

It will be the reverse of how the 7448 (cousin to 7447) converts 4-wire binary to 7-segment display:
Found at:
**broken link removed**

You will devise something like the above, but going in the opposite direction.

This will be a major challenge... unless someone else did it already, and was kind enough to provide a schematic.

 

[varunme]

My instrument have a segment display and there is a slot for extra 7 segment also, i want to use to connect to a PC or a uC

 

[embeddedlover]

But the question here is, who is controlling the 7-segment intially???? Unless, controlled, 7-segment can't light by itself.. Don't know if i am something here..

 

[betwixt]

If I understand the requirement, the OP wants to convert the drive signals to their 7-segment display into a format they can use elsewhere. A kind of 'revese 7-segment encoder' that does the opposite of a 7447/CD4511 device.

We need more information.
Is this a single digit or a multi-digit display?
Is the LED a common anode or common cathode type?
What format does it have to be converted to (binary, serial etc.)?
Does the signal already exist in the correct format, is there already a binary value being converted to 7-segment you can tap into?

Brian.

 

[varunme]

1 yes, revese 7-segment encoder
2 initially it is controlled by Atmega32 uC ( i dont have its code or anything).
3 common cathode, i cant tap the binary value (its occouring inside the atmega32 and just the 7seg line comes out to driver)
4 Its a two digit display
5 i want to tranfer into pc, through uart ( so any format is OK).

The instrument sends a series of values, i want to buffer it or send direct to uart through interrupt

 

[betwixt]

OK, that makes sense. What you need is a connection to each segment and also one to each of the cathodes.

You can do this in hardware but it is much easier in software: use a micro with a built in UART to make it easier to transfer to the PC. The program basically waits for each cathode drive to go low, meaning that display has been turned on then reads the segment signals into the program. From there, they can be used to look up the numeric equivalent of the segment pattern in a table. The result is passed to the UART and on to the PC.

There used to be a dedicated IC for this, I think it was a 74C917 but I doubt it's made these days and in any case it would only work on one digit at a time and you would still have to provide your own UART.

Brian.