Texas Instruments SR60A Repair(s) Quite a while ago I finally saw one of these machines on ebay. The listing said it wasn't working, but it was cheap, very cheap in fact, so I assumed it was indeed not working. It arrived. The case top was not attached and the display PCB was out of it's frame but that was easily fixed. Power on and: Do not power the printer without the control signal ribbon…
Recreating OPL The Psion Organiser II came with an on-board programming language called OPL. I had an organiser in the 80s and used it for quite a few things, some of which used small OPl programs that I wrote. It's been described as being like BASIC, and at the time I would have agreed. After heading into a project to recreate the language from scratch, I'd now disagree with that statement. OPL…
Making and Populating a Raspberry Pi CM4IO PCB RP CM4 The RP CM4 (https://datasheets.raspberrypi.com/cm4/cm4-datasheet.pdf) is a small processing unit capable of running Linux. It's cheap-ish and powerful-ish and useful for all sorts of things. It has many interfaces and RP designed a PCB to showcase these, it's called the CM4IO (https://datasheets.raspberrypi.com/cm4io/cm4io-datasheet.pdf). How…
Stainless Steel Sewing Kit Quite a while ago I bought a stainless steel cigar tube with no real idea what I'd use it for. I knew I'd do something with it, and finally I have. Now and again I do some sewing repairs and for that you need a few needles and some thread. On Kickstarter, also a long time ago now, there was a project for a container that held some needles and thread. I was looking…
What do you do if you want to dump the ROM in some equipment that is owned by someone else, who is happy to have their ROMs dumped, but who live in another country? they are probably not too happy sending things through the postal system as loss and damage is common these days. To solve this problem (and also allow me to dump some of my own ROMs) i made a little gadget that can dump a ROM that is…
This One Got Away From Me a Bit... I make pen sets occasionally, and to go with the set I make boxes. These are to hold the pen set and all the bits and bobs that go with them, and also provide a secure way to ship the pen set to it's final owner. Over time these boxes have become projects in their own right and have become themed, rather than being boxes. The latest box has sort of got away from…
Pens, Scutoids and a Box A combination of biology and mathematics was the theme for a recent pen box. It turns out that scutoids are a newly discovered shape that arrived with a fair amount of mathematics and biology. I decided to add them to a pen box that I was making. The result is here: These are 3D printed and covered in crushed velvet. Each one has a space inside that is big enough for a…
Coding With Rules of Thumb I create code quite a bit and have fallen into a process of using 'Rules of Thumb' or 'Meta Patterns ' when doing this. These rules aren't hard and fast and cover all aspects of working with code. I thought I'd document them, so other people can have a look and maybe use them. I also get a list of my rules, and a list of things can help spot missing and duplicated items.…
Chinese Questions It's always a good idea to have descriptive labels when coding, it is extra information that is useful for code comprehension. So: turn_the_light_on is a nicely description label, and light_on is a shorter way to name a procedure that turns a light on. If you have code that does something then you quite often have code that checks that the something has been done. This is code…
Code Comprehension Surely it's better to write this: romdata[addr-0x8000] = v1; romdata[(addr-0x8000)+1] = v2; like this: romdata[(addr-0x8000)+0] = v1; romdata[(addr-0x8000)+1] = v2; Ok, it's a bit more typing but it's easier to understand, surely?
Code the Specification: 6303 Assembler in 2000 Lines of Tcl Using Regular Expressions I have been interfacing to the Psion Organiser 2 recently, firstly using a Raspberry Pi RP2040 to replace a datapack and provide SD card storage of pack images: and also in the top slot of the organiser, which provides a way to add hardware to the organiser: When adding hardware in this way the organiser allows…
How fast is a Modern Microcontroller? At the time of writing, the Raspberry Pi Pico has just been released, so can be considered modern. How fast is it? Compared to the object of a recent project, the Psion Organiser II from the 80s, it is pretty fast. fast enough, in fact, to be able to pretend to be an EPROM in the Psion datapak. Some Technical Psion History The Psion Organiser II has two…
Transputer: Stack Based With OS in Hardware Picoputer: RP Pico Hardware Transputer The transputer was and still is an odd beast. It has hardware support for processes (hence OS in hardware, well, sort of), and its assembly language is such a pain that Occam is a much better way to program it. It's a language that is close to the hardware and allows parallel processing to be built in at a basic…
Reverse Engineering an LCD Display I have a DAB radio which started to irritate me in various ways. Finally fed up with it, I bought another radio and decided to free up the space that the old radio takes up by tearing it down. This is the DAB radio taken apart: Nice display 16 char 2 line dot matrix. Looking at PCB, it seems to have a three wire interface: Scoping up the lines, one looks like a…
Re-using a Broken Television as a Monitor or What To Do With a Broken Television when You Can't Fix It I was given a broken television. Technically this television was doubly broken: once when the HDMI inputs stopped working and once when everything stopped working. After the first fault it was taken to a television repair shop (yes, they do still exist) and they couldn't fix it as the parts are…
Miele Induction Hob Problems 2.0 The Miele hob has gone wrong again. The previous fix was a relatively simple capacitor replacement. This time things are not so straightforward. The initial fault was that the hob tripped the RCB in our fuse box when an attempt was made to turn on either of the front two rings. This happened several times. The hob was removed to the workshop to see what could be…
Novena Laptop Fix I got a Novena laptop from Crowd Supply several years ago. I didn't use it too much and that probably contributed to the batteries not being charged enough to maintain good health. That lead to some magic smoke being released from the battery charger PCB. It looks OK in this photo, but it's not. The laptop was dead at that point. Being open hardware, though, means that I have all…
Battery Leakage Again A recent purchase: It's a Casio FX502P in pretty much perfect cosmetic condition. Unfortunately the display isn't. It's not displaying anything very well at all. It's attempt at displaying Pi shows how bad the LCD is: Once I opened it up, the problem was immediately obvious. It was battery leakage again. It's not very obvious in this photo but the batteries have leaked in the…
Using a Thermal Printer Mechanism The Casio CP-10 is a neat calculator that has a thermal printer attached. The calculator also has a built-in clock and can do useful tasks such as printing this month's calendar. The date range is also useful as it ends in 2099. The printer is a small mechanism that take standard 38mm thermal paper. I found out that the mechanism is the same one that the FP-12…
Finite State Machines and the Software Hammer The firmware that runs the Casio FX502P gadget that I recently created has a structure and uses a technique that I though was worth documenting. The gadget uses the Arduino framework and is described in the following videos and blog entry . The prototype: This device has some tight timing constraints while performing interactions with a real-time…
Casio FX-502P SD Card Gadget Prototype A while back I made a gadget that attached to a Casio FX-502P via an FA-1 and stored programs and data on an SD card instead of a cassette . https://trochilidae.blogspot.com/2017/06/fx502p-cassette-interface.html It decoded the frequencies that the FA-1 sent to a cassette recorder and wrote the data to an SD card attached to an Arduino Due. I had to use a Due…
Casio CQ-1 Recreation Information Until I tidy up the github repository, here's some snippets relating to the Casio CQ-1 recreation. The first PCB is really a prototype as well, it just fits in the case better than the first prototype. The dc-dc converter that is used on the prototype is this one: https://www.ebay.co.uk/itm/401621208294 It's a variable converter and I worked out that about 23V is…
Reverse Engineering at -17V and 200kHz Warning: Rabbit Holes ahead I have a Rockwell 920/3 calculator. It's from about 1975, and is a pretty impressive beast. It's programmable and has 960 steps in its fully expanded form, a printer and a magnetic card reader/writer as well as a sixteen digit display. It can store data on cards as well as programs. The one I have (well the first one I got) ran the…
All This to Get Back Where It Started Storing scrap PCBs is all well and good but what do you do with them? After buying a vacuum desoldering machine (wonderful piece of kit), I decided to dismantle the scrap PCBs that I'd been holding on to for years. One of the PCBs I removed components from was a VCR which had a large vacuum fluorescent display on it: Underneath the display was a controller…
Is This the Past, or the Future? We have a rainwater harvesting system, which comprises a large tank in the garden fed by rainwater, a submerged pump in the tank and a pump controller in a cupboard in the kitchen. Yesterday our washing machine that is fed from the rainwater had it's red 'Check input' light on. Not good. What was even less good was the water that had been squirted up onto the roof…