In the summer of 2014, I had the grand idea of building my own calculator. I had just acquired a Raspberry Pi, and was tinkering around with TilEm. So I planned it out.
First, the basics. I need a power source, a screen, and a keypad. I found a 3Ah Li-Po pack on Amazon that was about the same dimension of a standard 83 and could put out 3 amps of power at 5 volts with the converter that came with. The screen was an easy find too, I harvested that out of a cheap car rearview-camera system from Amazon (I had to find one that I knew would run off of 5 volts). But the keypad was a lot more difficult.
My immediate thought was to buy one of the 84 keypads for the N-spire and modify it to work with the Raspi, but since I don't have the money to shell out for/the experience to modify one of those, I turned to another option: building one myself. I aimed to re-create a calc from the 83 series, so I needed 50 buttons. And TilEm is happy to accept keyboard input (and in fact prefers it), so I needed to build a custom 50 key keyboard. So I went online and got a cheap USB keyboard and 100 momentary switches. I tore out the microcontroller from the keyboard and, looking at the key membrane, mapped out which contacts would produce what keypresses in a grid (I have since lost the sheet of paper I did that on). After that, I chose which 50 I wanted to use, modified TilEm's keymapping to accommodate, and started constructing my keypad using breadboard and strands from old ribbon cable. It was a beast to do, took me about 30 hours in total (that's just the keypad).
So, I have all of my parts, and they all work, so now to build, right? Well, I totally underestimated the accumulated thickness of all of my parts, which now had grown to include a USB hub and a selection of throws and switches. I, at the time, had no access to laser, cnc, 3D-print, or other "modern" construction techniques, so I defaulted to what I knew best: crude woodworking. And when I say crude, I mean it. I chopped up pieces of dowel rods for the pushbuttons and drilled holes in slabs of wood for the faceplate. More thin slabs of wood for the rest of the case, and hotglue and tacks to hold things together. It looked rough, but it worked. The physical build was complete.
Software wise, I already had TilEm starting at boot and modified its keymap to match my homemade keypad. Now I needed to get rid of the cursor, make the Emu fullscreen, and find a safe way to shutdown (cutting the power abruptly proves to fry SD cards after a month of regular use, I learned that the hard way). I found a way to get rid of the cursor and fullscreen the program in XFCE, and wrote a Python script to poll a pin every 2 seconds to check if it's high (and if it is, it runs a "sudo halt"). And now it works the way it should.
So there it is, my homemade calculator.
Pictures!!
http://i.imgur.com/ToLo2yN.jpg
http://i.imgur.com/e1mBUka.jpg
http://i.imgur.com/y7h5Mz0.jpg
http://i.imgur.com/veZ3GMa.jpg
http://i.imgur.com/taxZToG.jpg
http://i.imgur.com/oERDipz.jpg
http://i.imgur.com/e6X0jAu.jpg
http://i.imgur.com/9IdLVeE.jpg
http://i.imgur.com/pjoQaSX.jpg
http://i.imgur.com/n1EKYJq.jpg
Things still left to do:
Fix the black border
Re-image the SD card with a lighter-weight distro
Get rid of software that slows it down
Update TilEm to include color and link support (linking to GPIO pins would be cool, so hardware linking would happen, just an idea)
Build a slimmer version
I estimate I spent about 200 hours on this project in total last year, and the parts cost me around $110USD in total. I did this all before I found the Cemetech community, and I did not take many pictures along the way, but I'll be happy to discuss what I remember from the build process. I have been meaning to share this with you all sooner, but I never got around to it. I have used this thing extensively in Pre-Calc and Chem class, and plan on continuing its use through Calculus, Physics, and college.
First, the basics. I need a power source, a screen, and a keypad. I found a 3Ah Li-Po pack on Amazon that was about the same dimension of a standard 83 and could put out 3 amps of power at 5 volts with the converter that came with. The screen was an easy find too, I harvested that out of a cheap car rearview-camera system from Amazon (I had to find one that I knew would run off of 5 volts). But the keypad was a lot more difficult.
My immediate thought was to buy one of the 84 keypads for the N-spire and modify it to work with the Raspi, but since I don't have the money to shell out for/the experience to modify one of those, I turned to another option: building one myself. I aimed to re-create a calc from the 83 series, so I needed 50 buttons. And TilEm is happy to accept keyboard input (and in fact prefers it), so I needed to build a custom 50 key keyboard. So I went online and got a cheap USB keyboard and 100 momentary switches. I tore out the microcontroller from the keyboard and, looking at the key membrane, mapped out which contacts would produce what keypresses in a grid (I have since lost the sheet of paper I did that on). After that, I chose which 50 I wanted to use, modified TilEm's keymapping to accommodate, and started constructing my keypad using breadboard and strands from old ribbon cable. It was a beast to do, took me about 30 hours in total (that's just the keypad).
So, I have all of my parts, and they all work, so now to build, right? Well, I totally underestimated the accumulated thickness of all of my parts, which now had grown to include a USB hub and a selection of throws and switches. I, at the time, had no access to laser, cnc, 3D-print, or other "modern" construction techniques, so I defaulted to what I knew best: crude woodworking. And when I say crude, I mean it. I chopped up pieces of dowel rods for the pushbuttons and drilled holes in slabs of wood for the faceplate. More thin slabs of wood for the rest of the case, and hotglue and tacks to hold things together. It looked rough, but it worked. The physical build was complete.
Software wise, I already had TilEm starting at boot and modified its keymap to match my homemade keypad. Now I needed to get rid of the cursor, make the Emu fullscreen, and find a safe way to shutdown (cutting the power abruptly proves to fry SD cards after a month of regular use, I learned that the hard way). I found a way to get rid of the cursor and fullscreen the program in XFCE, and wrote a Python script to poll a pin every 2 seconds to check if it's high (and if it is, it runs a "sudo halt"). And now it works the way it should.
So there it is, my homemade calculator.
Pictures!!
http://i.imgur.com/ToLo2yN.jpg
http://i.imgur.com/e1mBUka.jpg
http://i.imgur.com/y7h5Mz0.jpg
http://i.imgur.com/veZ3GMa.jpg
http://i.imgur.com/taxZToG.jpg
http://i.imgur.com/oERDipz.jpg
http://i.imgur.com/e6X0jAu.jpg
http://i.imgur.com/9IdLVeE.jpg
http://i.imgur.com/pjoQaSX.jpg
http://i.imgur.com/n1EKYJq.jpg
Things still left to do:
Fix the black border
Re-image the SD card with a lighter-weight distro
Get rid of software that slows it down
Update TilEm to include color and link support (linking to GPIO pins would be cool, so hardware linking would happen, just an idea)
Build a slimmer version
I estimate I spent about 200 hours on this project in total last year, and the parts cost me around $110USD in total. I did this all before I found the Cemetech community, and I did not take many pictures along the way, but I'll be happy to discuss what I remember from the build process. I have been meaning to share this with you all sooner, but I never got around to it. I have used this thing extensively in Pre-Calc and Chem class, and plan on continuing its use through Calculus, Physics, and college.
How about adding some software to support emulating other calculators too (like the 89)?
