Monthly Archives: October 2023

Microprocessors, PICO, Raspberry Pi, Retro

Pico Lynx

A Pico Emulated Camputers Lynx

The Camputers Lynx was a classic, although not massively popular computer in the early 1980’s. It featured a z80 at 6Mhz and full colour graphics, with none of the BBC micro’s (or others) Graphics mode shenanigans. And for its time many advanced capabilities like 96K memory, a disk system (later upgradable to CP/M 80), and a proper keyboard. Unfortunately it hit at a bad time, the Spectrum was much cheaper, but much less capable, and the BBC was being pushed massively by the BBC (unsurprisingly). It’s eventual down fall was that its brilliant graphics were both quite slow and due to its strange memory banking system, rather hard to program. Eventually it lost out due to the lack of game titles compared to the Spectrum and BBC Micro/Electron.

But I had one and I loved it (latterly I had three)

Camputers Lynx (By Retro-activity, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31282859)

I already have a PCB that Ive used for Pico Emulation of a number if things, so that was my go to as a start.

I had asked for permission to use the code by Charles Peter Debenham Todd retrogubbins (as there is no licence on his GitHub pages) and he graciously let me use his code with no restrictions.

I based my Pico design on his PALE emulator and his ESP 32 emulator https://github.com/retrogubbins/PaleESP32VGA

One of the first issues I had was that the Z80 emulation that he used did not have any licence either, so early on I swapped it to LIBZ80 © Gabriel Gambetta (gabriel.gambetta@gmail.com) 2000 – 2014 which is currently maintained by EtchedPixels as part of the z80 emulation kit https://github.com/EtchedPixels/EmulatorKit

I’ve used this library before in the RC2040 So familiarity was on my side too.

Swapping over the emulator and porting the ESP32 code to the Pico was amazingly straight forward, I needed to write some code to DMA out the RGB banks to a display (240×320 OLED) and I quickly got a Lynx prompt.

Unfortunately it was in Yellow, and the emulation stopped there. I took me a while to get past this, until I realised that the Lynx Beeps, between writing the Red and Green banks, and before writing Blue. I hadn’t implemented the code for the sound / speaker.

Adding this in gave me not only a while logo, but two power up beeps, and (after spanering in serial to the keyboard emulation ) a workable basic.

So time to make a case.

I took the measurements from a real Lynx and scaled it to roughly fit the keyboard I had with the PicoPuter. It came out as roughly 1:3

Of course Not everything fitted correctly, so after a few goes.

I got one that fitted and held the PCB’s in roughly the right place.

Of course I needed a monitor, so I did a quick 3D print of an IBM 5151 style monitor. This gave me the space to the right to hide the display connector. and as the original was only 12″ didn’t look out of place with the small Lynx Case.

For the keyboard I wanted actual working keys.

So I made an escutcheon from grey sprayed card

and laser cut/engraved a set of small keys to fit. Because I couldn’t get grey acrylic I used transparent acrylic, on top of a grey sprayed key holder.

The effect is grey keys with white painted idents.

Not 100% happy with these, but I have a set for working grey keys, on a grey Lynx shaped case. For a more accurate layout I’d need a custom Lynx keyboard PCB.

The whole case is only 120mm wide to give you some idea of scale.

The two PicoPuter PCB’s sit inside and a small battery, because it was vital for this to run as a portable 🙂

The Ribbon cable is the feed to the display, which is mostly hidden by the case and the display itself.

and attached to the back of the display by a small daughter board.

Uncategorized

Notts Gaussfest – What is a Gaussfest ?

          What is a Gaussfest ?

Nottingham Gaussfest is a yearly meeting of a loose group of friends sharing a common interest in high voltage equipment and Tesla coils.In the USA these meetings are always referred to as Teslathons, a reference to Nicola Tesla who’s tesla coils always feature prominently at these events. We decided, being European, we would adopt Carl Friedrich Gauss as the scientist, due to all the devices also required a high magnetic field and we wanted to differentiate ourselves. Hence the term Gaussfest.

The equipment that appears at the Gaussfest is entirely dependent on the Exhibitors present, and their current interests. Usually there will be a collection of various types of Tesla coils, and a collection of static electricity generators like Van-De Graff machines and Wimshurst machines. But each year someone surprises me with something different, or new.

Tesla coils are the most common high voltage device we get, are essentially a large transformer. Near the bottom of the tesla coil is a radio frequency generator either electronic or mechanical, driving a primary winding with a small number of turns. The Secondary coil (the tall one) has a much larger number of turns of around 800-2000 turns typically. And at the top if this, a topload where the high voltage comes out. We get tesla coils of all sizes from a 50mm high, to over 2M tall at the Gaussfest.

The Static generating machines our exhibitors bring are even more are varied. The common ones are a Van de Graaff machine, uses a belt to transfer charge up to the top dome where it is stored, and the Wimshurst machine uses a pair of contra-rotating disks to multiply charge and store it into a pair of capacitors. Again the sizes of these machines vary from 200mm tall to 1.5MAlthough the electrical discharges from these machines look dangerous, they are entirely safe if viewed from a distance, and our exhibitors are very experienced with the operation of their machines.

Or Exhibitors are happy to talk about how their machines work and the problems with their construction, although if they are preparing them for a demonstration, or have problems please give them “thinking room” as their safety, and the safety of their equipment is paramount. All our exhibitors are all amateurs and make and demonstrate high voltage equipment for fun. The Gaussfest is their opportunity to display what they have been working on.

Commercial high voltage engineering is expensive, due to this many of the exhibits on display will have been made totally or partially from household items, surplus, and any available electronic equipment, often with items multiplied up to deal with the high voltages/currents that are required. To keep the cost down, the equipment is usually run at the very maximum of its tolerances. These devices are rarely engineered for their longevity, so failures are quite common, and this trade-off is very much part of the hobby. Due to this, we do not have planned schedules for the demonstrations, as equipment WILL FAIL (and be repaired) during the day, although we will endeavour to have something always happening.

When the Gaussfest moved to Papplewick in 2017, we were very conscious that for us to do our activities, Papplewick pumping station must get something back, So Papplewick allow us to meet, and we let the public see what we do and give demonstrations to give back to the Pumping station. As much of what we do can be dangerous, this trade-off is some restrictions in access to the station to ensure your safety.  

Nottingham Gaussfest

Gaussfest registration