Designing an FPGA Calculator from Scratch

5/18/2026 at 10:22:07 PM

Ten minutes in it looks like a great project walkthrough from design to physical device build.

Good start for anyone interested in the guts of going from logic gates to math() primitives ( add, mult, tan, sin, etc ).

Two snippets from the lede, one from a chapter heading:

  This is a scientific BCD calculator that uses binary-coded decimals, the same internal number format HP used in its scientific calculators going back to the 1970s. It represents every decimal digit as a 4-bit nibble, which means perfect decimal accuracy, no floating-point conversion errors, and an architecture that is genuinely shaped by the problem it solves. 

  Across ten chapters, you will follow full arc: the architectural decisions and tradeoffs, the numerical algorithms (addition, multiplication, CORDIC for trig, logarithms), the custom CPU design and its 12-bit instruction set, a hand-written two-pass assembler in Python, the microcode that runs on that CPU, a scripting layer for high-level key functions, and finally the physical board with its battery, display, and keyboard.

Chapter 6 (of 10):

  No general-purpose CPU has nibble-addressable memory and addressing modes designed to walk a 16-digit BCD mantissa — so this post designs one.

I like it.

by defrost

5/21/2026 at 3:41:38 AM

I like FPGA projects, but there is really nothing preventing you from implementing decimal arithmetic in software on a cheap microcontroller.

by musicale

5/18/2026 at 11:40:44 PM

I would love to have some real application that needs an FPGA :) Someday perhaps.

by foota

5/19/2026 at 1:38:50 AM

You would perhaps need to change the viewpoint for that. Theoretically, there is nothing which can't be achieved - functionally - without FPGA. However, that doesn't mean some problems can' be solved more conveniently using FPGA, and the solutions turn out better in some regards.

by avmich

5/19/2026 at 1:57:35 AM

Could you share some of those applications which are better solved with an FPGA? As a student I have some ideas but am interested to hear more.

by atultw

5/19/2026 at 2:26:40 AM

OTOH, I recently learnt that Jane street deploys their own FPGA servers for high frequency trade.

by Imustaskforhelp

5/19/2026 at 3:25:01 PM

Got a link for the writeup/post from them?

by tonetegeatinst

5/19/2026 at 7:23:31 PM

did a quick search to see this post from janestreet: https://blog.janestreet.com/advent-of-fpga-challenge-2025/

But I too was (edit: also still am!) interesed in fpga so I was just scrolling and I found this really really great video (I can't recommend this enough, so much so that before reading your comment that I actually submitted that video as HN submission)

The video I am talking about is this: https://www.youtube.com/watch?v=d3nuepnbmC4 (FPGAs Aren’t Processors (Unless You Want Them to Be) || FPGA Deep Dive and Use)

Also check out what this guy has been doing with old factory robot machines and using FPGA for them was a really practical use of it and they have another video about it too that you can find on their channel.

Some parts of the video especially near the end went really really out of my head but this might be one of the best videos about FPGA judging from the comments and I just really loved it man, so that's about it yeah, I recommend watching the video!

by Imustaskforhelp

5/19/2026 at 8:34:44 AM

i was thinking of using FPGA to control led matrix, the algorithm is not hard, it's just there are too many pin to control, they need high clock rate if you want high color depth, a using MCU bit bang is not really a choice.

by mrheosuper

5/19/2026 at 10:53:52 AM

And Colorlight i5/9 boards are made for that very application; it just so happens they're a reasonable minimal devboards for ECP5 FPGAs. I don't think right now you can get anything more capable for the price (Yeah, there are super cheap decommissioned miners with Zynq, but there's almost no I/O fanned out.)

by RicoElectrico

5/19/2026 at 8:11:59 AM

Hard real-time control systems is one application.

by i_don_t_know