RPN-duino

[Chasfield]

That is a very good idea. Thank you.

[BobVA]

(03-27-2017 03:58 PM)Maximilian Hohmann Wrote:  Couldn't you show them on the display in some way, e.g. when the calculator has been idle for some time?

Regards
Max

Or perhaps call them up with the center push, if you can add some code to catch and discard any resultant inadvertant directional pushes? (Sort of like a keyboard debounce) Or maybe with a "long push" to a direction?

Nice project!!

[Chasfield]

After tidying up the built-from-parts joystick calculator, I decided to produce something similar but with a much higher specification. I have stretched the low cost Arduino Nano to its limit, with my code bumping against both RAM and flash memory ceilings. However, The Arm based Arduino Due is much more powerful and packs 96 KB RAM and 512 KB flash storage. It also has about a zillion I/O pins. The big deal with this device is that it supports true double precision floating point maths.

For the physical hardware I have gone for a 1.3 inch OLED - these can be had for what a 0.96 inch unit used to cost. I have conjoined two Farnell 4x4 keypads to give 32 keys. Some minor "chopping" was necessary to reduce their footprint. The makers have upped the spec. of these as the key tops are now of double-shot construction, which is not so useful to me. For example, on the last calculator I was able to scrape away at the letter "B" to leave a pretty decent decimal point! Also the back of the keypad is now heat staked rather than screwed on, which made moving the key tops around from phone to calculator layout a bit more difficult.

I have attached a picture of the Due based calculator in a fairly raw state, sans keyboard labels.

It is displaying the result for the tan(355/226) trig torture test. This makes me happy.

[Luigi Vampa]

Good to see you back again in action. Thanks for sharing your latest design. Please, keep us posted about the progress :O)

[EugeneNine]

Those keypads look very similar to the one(s) I had but mine were 5x5 and the bottom row of buttons had clear removable keycaps so you could place your own labels. I wonder if those are still made.

[Chasfield]

The Due calculator has progressed. It is a bit of a brick since it is built around a Due board with header sockets and runs off a PP3 battery. A much lower profile device would have resulted from using a solderable Due PCB combined with a LiPo battery plus charge controller - that will be a project for the future.

Otherwise things have gone well. Compared to the regular Arduino, this thing goes like a rocket. It computes 170 factorial in the same subjective time that it takes to add 2 + 2 and the I2C connected display responds with no perceptible lag. The relatively huge RAM space allows for the reckless use of a variety of u8glib display driver fonts. With my previous designs, I had abandoned this convenient graphic device library and resorted to writing my own display driver code to avoid running out of RAM variable space.

Attached is a picture of the calculator in its alternate high precision one line display mode showing the answer to 170 factorial.

The only fly in the ointment is the documented hardware bug on the Arduino Due R3. From a cold start it runs the boot loader instead of your code and sits there doing nothing. A subsequent power cycle or hard reset is necessary to get your code running. There are hardware and firmware fixes for this, but right now I don't want to blow my board up. The problem was fixed on newer releases of the board.

[Dan]

That is so cool. Has both a retro and futuristic look to it. I see there is no "grads" for angles. In all my years of learning and teaching math I've never used grads. Does anyone use them?

[larthurl]

nice job!
Reminds me of when, in 1976, I built my own apparatus to compare calculator and telephone keypad layouts for my first master's degree. I got two free calculators from Sinclair, kluged a 4x4 keypad (one of which had key layout and contacts changed). Built a 5v power supply and away I went. I believe I used an HP-45 for my data analysis.


.....Art Leyenberger

(10-16-2015 03:55 PM)Chasfield Wrote:  I have been busy with a home brew RPN calculator project based on the Arduino Nano mini board. The impulse to get going with it came from finding an Arduino starter kit that had been sitting unused since last Christmas, linked to the discovery that Rockwell once turned out four banger calculators with an easily detachable modular keyboard. I cannibalised a 20 key unit from a model 18R. These keyboards have a nice, almost HP48-like action and are perfect for adding custom key labels to. These old calcs are cheap on auction sites.

As the pictures show, I finished up with a fairly chunky device in a custom case. It features varnished pine trim, which I believe is a first for calculators!

The back-lit display is the ubiquitous and ridiculously cheap 2x16 character 1602 unit. And power comes from a PP3 battery, which should be good for about 20 hours use at 30 mA current draw. That isn't bad, given that the calculator has a real on/off switch. A reflective type LCD would double the battery life but I quite like the blue and white glow of the one used - easy on middle aged eyes as it is.

Calculating accuracy surpasses the Sinclair Scientific by a couple of decimal places but floating point maths is not a strong feature of regular low cost Arduino boards. At the moment, standard form number handling isn't programmed - big/small numbers with exponents display as 0. Digging the bits of them out of Arduino "float" type variables and doing something useful with them is a project in progress.

[Luigi Vampa]

I like all your DIY approaches.
BTW, since I was a child, I have always had a "middle-aged sight" 8') I have always preferred bigger-than-usual fonts.

[Chasfield]

Attached are a couple of pictures of my latest calculator build. I had been looking around for a better platform for these projects after taking the regular 8 bit Arduino as far as I wanted. The ARM-based Due model used in my last lunch-box sized calculator was great to program and it handles double precision floating point maths effortlessly but the PCB is physically quite large and that project's power consumption is relatively high at 50+ mA. After convincing myself that The PJRC Teensy 3.2 would do 64 bit maths out of the box, I laid out 20 GBP to acquire one. The specifications are just right: Cortex M4, 64K RAM, 256K flash ROM and it is powerable from a single 3.7V LiPo cell. The unit is smaller still than an Arduino Nano. The resulting calculator is almost Casio sized!

The picture of the underside shows the layout of the components and this time the construction is boxless, with the siamesed 16 button keypads forming the top deck. Side rails are 8x8mm acrylic bar and the lower case cover is cut from 3mm acrylic sheet. The Teensy 3.2 is soldered directly onto the lower keyboard's header pins, which takes care of most of the wiring. Keyboard column pins are commoned via ribbon cable. A second ribbon cable connects the row pins of the top keyboard to the Teensy. Charge control of the LiPo cell is taken care of by one of those ubiquitous little controller PCBs that seem to cost only their postage on eBay. The 1.3 inch OLED display connects to the designatd I2C pins on the Teensy (these displays are getting cheaper too - 6 GBP).

The display is driven with the u8g2 display library and the display code from my Due project only required minimal tweaking to work on the Teensy. The standard Arduino IDE accepts Teensy extensions that are downloadable from the seller's web site. For minimal power consumption, the device is throttled down to 48 MHz clock speed and the calculator draws around 35mA from the 800mAHr LiPo. It took me a while to shake out the full 64 bits from the math.h library. By default, a compiler flag (-fsingle-precision-constant) is set by the IDE that restricts declared constants to 32 bit float precision even when they are defined as 'double'. Once this was edited out of the Teensy 3.1/3.2 section of the IDE's boards.txt file, the math.h library worked properly and the calculator delivered full precision.

[Luigi Vampa]

Wow! Really cool design. Congratulations!

[larthurl]

(09-17-2016 02:49 PM)Chasfield Wrote:  I stumbled upon an old thread (which I can't now find) in which a forum member had reworked a Texas TI 1025/1050 four banger into a capable RPN programmable. These cheap units were produced in huge quantities and are great for hardware hackers. There is loads of space inside at the thick end, with moulded-in clips for a circuit board. The spacious metal face plate was just made to be re-legended and the keyboard module header lines are robust and accessible with a soldering iron.

Anyway, attached is a picture of my project based on a TI 1025, which now runs an Arduino Nano and 1.3 inch OLED display. This allows a full 4 line output. The original Texas unit featured software on/off switching so I wired a real power switch into the lower casing.

With 24 keys to play with, I was able to add a few extra stack orientated features:

S^2: square all stack registers
1/S: take reciprocal of all stack registers
SS: Sum stack
TVM: loan payment calculator where r=Z, N=Y, PV=X

The build went smoothly and the only problem is that the display is a bit dim for a sunny day thanks to the very heavy filter factor of the grey acrylic cover.

that looks fantastic. Looks like a real production mode. haha!
Where's the Enter key, or did I miss it?

[larthurl]

(10-16-2016 03:41 PM)Chasfield Wrote:  I decided that I would have a shot at building a functional clone of an HP35. A four-line OLED display, coupled with the clean-sheet ergonomic design of HP's original machine, looked like a route to building something that would be nice to pick up and use.

Making a satisfactory keyboard is the hard part. I ordered up 50, 12x12 mm tactile PCB switches of a type which feature a 6 mm deep extended actuator. I took the best 36 of these to populate the keyboard and made doubly sure that they all fired at the click before I committed them to epoxy cement. The result is, I reckon, aesthetically satisfactory and it is ok to use if you were able to get along with a TI59 back in the day.

The attached pictures show the calculator's construction method and soldering nightmare.

Right now, the OLED display is held up at the docks but I have plenty more coachwork tasks to complete and a battery compartment to construct.

Despite the way it looks in the last picture, I would say that 85 percent of the job is done, given the 15-20 hours spent getting a labelled keyboard up and running on a serial console test script.

so cool! thanks for sharing.

[Luigi Vampa]

... it seems to me it would be the purple one labeled as "ENT".

[Chasfield]

I think the question related to my earlier TI 1025 with the brain transplant and display upgrade. On that calc, enter is top left, marked with a right arrow - the best my Brother label machine could offer. The plain white key gives the shifted functions.

A Teensy 3.2 would go nicely in that one too!

[Chasfield]

I have been working at reducing the power consumption of the Teensy 3.2 based calculator. Setting the clock frequency to 24 MHz reduced it to 25 mA, with the display showing four lines of zeros and the device waiting for a key press. This had no subjectively observable impact on response or performance.

I decided to try something fancier and added Duff's Snooze library to the sketch (it was inclded with the Teensy extensions for the Arduino IDE). I replaced a 10 ms delay that was set in the main keyboard loop with 10 ms of sleep. This produced good results. The calculator now idles at 7.5 mA, which is a very modest burden for the 800 mA LiPo battery to carry.

Thank you, Duff!