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I know this is very unusual but I need it. A PLC has outputs to drive 7-segment display. However, I have a new device that works only with Gray Code or Binary. This new display and the old 7-Segment will be working together. To do this, I need a circuit converting 7-Segment output to Binary or Gray Code.

Is there any such thing? Or how can I do this?

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  • \$\begingroup\$ If the plc program can be reached you could solve the problem inside the plc program. For a 7 segment you have the a-g and the dp. Therefore 8 outputs. For a Binary or Gray code you will only need 4 outputs and the dp. The multiplex selector driving the individual digits remains the same. Therefore you need to add only 4 outputs. Maybe they are available or else an extra module is required \$\endgroup\$ – Decapod Oct 12 '16 at 6:48
  • \$\begingroup\$ @Decapod you're right but I dont want this to cost too much with extra plc module. I'm asking if there is a way to do with prebuild circuit. \$\endgroup\$ – jakarina Oct 12 '16 at 6:58
  • \$\begingroup\$ @jakarina: Can you do away with the old display all together? If so then you could change the programm without an extra module. A different approach but maybe possible is to use an arduino and program the thruth tabel. The arduino Uno has sufficient channels and is not expensive. Do not forget the voltage levels you have to work with \$\endgroup\$ – Decapod Oct 12 '16 at 7:02
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    \$\begingroup\$ Are the segments multiplexed, and how much cost is too much? \$\endgroup\$ – EM Fields Oct 12 '16 at 7:46
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The 4511 IC is a standard component used for driving a 7-segment display. It takes a BCD input and provides the output signals for a 7-segment digit.

I'm not aware of any standard IC that does the opposite conversion.

The best way to do this, as @Decapod mentioned in the comments, is to do this in the PLC logic, editing the program to use 4 new output points. However, if you don't have editing access to the program, or you don't have 4 spare outputs, this might be difficult.

An alternative is to use an intermediate controller to do the conversion. An Arduino or other microcontroller is inexpensive and could work. Another alternative is to put in a small PLC just for this purpose, which might match your voltage signal requirements better and are already packaged for an industrial environment. (The Click PLC from AutomationDirect is one example.) The programming of these are quite simple, and I have a hard time believing that you would be able to purchase a pre-built one-purpose module for less than the cost of one of these small PLCs.

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If you want to convert 7 bits (7-segment) to 4 bits (binary), a programmed PROM with 7 or 8 adress lines and at least 4 bits output will do. But if you want to convert several decimal digits of 7-segment code to a binary number you would need a larger PROM. For two digits a 16 kbyte PROM will do ( 14 inputs, 7 outputs). But for three or more digits fairly large PROMs are needed. A cascaded solution is difficult because of the multiplication with 10 and the binary addition. Using a microcontroller ist the better solution for several decimal digits.

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