I want to confess. I wrote a lot of projects for hackday, but few I read, and then actually built a copy. I don’t have much time, and I’m usually busy building my own things. But occasionally, I will think of something. I will search the dustbin or buy tools. The latest example is the px-41c, which is a replica of the classic hp-41c.
Beautifully packaged parts.
Hp-41c is a legendary reverse Polish symbol calculator. I still keep the original hp-41c from 1979 (the serial number is very low). It’s still a working horse, but when I was about 43, I didn’t like to hang it near anything that might damage it. From the daily use 40 years ago, it is durable enough. Of course, I have a good simulation on my phone and I use it, but the px-41c suite looks interesting and has all the through-hole parts, which will be a fast build. Tindie’s Black Friday auction finalized the deal for me.
start-up
The kit arrived on Saturday after Thanksgiving and I decided to process it while waiting for 3D printing. These parts are well bagged and marked. Tearing the bag is a bit frustrating, but it’s not difficult. It really separates everything. There is a list of materials, but – I think – there are no instructions. The last part of the bill of materials is a link to some instructions. They are not many. I didn’t realize their importance until I finished the board of directors, but it’s not difficult to understand. All the parts are marked on the silk screen, and you may find it – there are some precautions.
Note that the components of the LCD are flattened.
There are several components under the LCD screen. They are welded together, so you need to put them in first. I wonder if you should install them on the back of the circuit board, but the photos show that they are installed on the front. You will soon realize that you have to bend them down and let the LCD flat. If you read the instructions, be sure to mention it.
Once I’ve done everything except the switch, I’ll power on to make sure everything is normal. It did start, or at least started, saying that memory was lost.
switch
39 switches require 156 solder joints
A total of 39 small tact switches need to be installed. Fortunately, their legs are small enough to reach into the hole, so it’s not difficult. However, they may pop up, so I suggest doing one or two columns at a time. One switch was a little bent, but there was an extra one, so I didn’t bother to untie it.
There are several keys in the lower right corner. I can turn on the power and calculate quickly. There is no problem. The board took the cr2025 and I had only one thinner battery. A dime made a good interval. Let me install a thin battery and make it work.
to configure
The circuit board has a backlight LCD and a clock – with functions that ordinary hp41c does not have. However, I don’t see an obvious way to set them up. At that time, I had found the document, which said that when powered on, press and hold the 0 key to enter the configuration menu. It turns out that this is a division key, which takes a minute to calculate. In addition, the keys of the operating menu system are a little unstable (but, to be fair, the firmware will display a help message on the screen until you release the divide key).
Just in case
The housing looks great and the key spring is very accurate. The tape on the covering layer is very obvious in the photos, but it is not so bad on people.
There is a 3D print box and a method to print an overlay key and an elastic key matrix. They sent me these already made ones very well, although I’m not sure if they are always included. The overlay looks great at first, but if you look closely, it’s stuck with tape, which will be a little damaged. Don’t hold up the tape! It will destroy the overburden.
The case looks good and quite simple. But there are some problems. First, the liquid crystal display protrudes upward at a certain angle. The instructions tell you to stick it to the CPU, but it doesn’t really help. After taking these photos, I unplugged the LCD and carefully reinstalled the new title to make it look beautiful and flush.
Another problem is that the R / s key in the lower right corner does not want to work when the box is in place. Sometimes it doesn’t work. Sometimes it works, but it’s more like a touch panel than clicking on other keys. Sometimes it gets stuck.
I tried to file the case a little, but it didn’t seem to work. Some protrusions prevent the circuit board from falling too low on the key spring. It seems that the box is bent hard enough. That corner is a little lower than the other corners. If you do not use the backrest, but push hard at that corner, this will reproduce the problem, but there is no problem at other corners.
I’m thinking about reprinting the case myself – after all, I have enough 3D printers. But I finally made a small paper gasket to make the stop in that corner thicker. I just took a small piece of paper and folded it many times until it was about the size of the stop. Then I inserted the stop into the paper and made a sandwich. The paper was bread and the stop was meat. This seems to solve the keyboard problem. It seems that the problem has nothing to do with the key installation, but everything is possible. I’m sure it’s just a subtle distortion.
Last impression
Done. To some extent. Good! The tape is very reflective in the picture.
Price (about $40) this is an interesting toolkit that is actually useful. If only the LCD had a socket. It’s good if the overlay installation looks cleaner, but at a glance, it’s good and still looks better than a bare PCB with keys – unless you like that.
I haven’t tried to see if the simulator will do synthetic programming, but it’s on my task list. Otherwise, I can now use my hp41c without my mobile phone, and I don’t have to risk my real mobile phone. After more than 40 years, it can use the rest.
For some reason, I tend to build projects after writing (or reading) articles about them, mainly for retrospective calculation. I built Kim uno (and repurposed it in 1802). I built a pidp-8 (need to make time for PDP-11 version). Maybe my favorite is the $4 Z80. I actually add a little in software.