I've been trying to make a decimal calculator using binary adders that feed into 3 x 7 segment displays. I cant find an efficient way to do this. If someone could point me to the correct resources, or maybe show a circuit that you made that is similar, that would be greatly appreciated.


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    \$\begingroup\$ Look up for BCD \$\endgroup\$ – Gregory Kornblum Nov 8 '18 at 18:29
  • \$\begingroup\$ It's a rather difficult task. Have you considered using a microcontroller? \$\endgroup\$ – user28910 Nov 8 '18 at 18:30
  • \$\begingroup\$ @user28910 My goal is to use only IC's or logic gate (on IC chips). Will I have to use 100's of gates? \$\endgroup\$ – Karl Streitz Nov 8 '18 at 18:33
  • \$\begingroup\$ An FPGA could work too, if your purpose is to gain experience in logic design as opposed to embedded programming. FPGAs and microcontrollers are both ICs. Or, look up BCD converters as Gregory mentioned. \$\endgroup\$ – Justin Nov 8 '18 at 18:36
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    \$\begingroup\$ Do your arithmetic in BCD, use BCD to 7-segment chips for the display. You may have to go digging for obsolete parts, because today's answer is to just use a microprocessor. \$\endgroup\$ – TimWescott Nov 8 '18 at 19:04

If you're doing this with discrete IC's, like 74xx series, you need a binary-to-BCD converter. Searching on that phrase turns up the DM74185 [http://www.utm.edu/staff/leeb/DM74185.pdf] (the companion DM74184 goes the other way). BCD is Binary Coded Decimal -- 4 bits per digit, encoding 0-9. Then the outputs of those can go to BCD-to-7 segment converters, to the display.

For a 3-digit display (0-999), that's 10 binary bits, and you would need 5 or 6 of them. The data sheet shows how they get cascaded together.

However, further search on those part number comes up a little light, so those chips might not be common anymore.

In modern times, you would build a calculator with a microcontroller. But if you want a hardware learning experience, you could do this on an FPGA, like the Go Board [https://www.nandland.com/goboard/introduction.html]. You would use Verilog or VHDL to describe the circuit you want. It's not like programming a microcontroller; you're describing a circuit that gets "wired up" in the FPGA, just as if you built it from gates. But there is a significant learning curve for the tools and methods.

  • \$\begingroup\$ You are the best. You've ended my year long electronics struggle. \$\endgroup\$ – Karl Streitz Nov 8 '18 at 19:59

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