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A quick update

26/3/2020

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My day job has been insanely busy the last few weeks, and to be honest the last thing I've felt like doing was spending time hunched over a soldering iron or more time behind a computer screen. 

I work for the NHS and all this virus business is to say the least depressing, so I decided to shutdown my twitter account (so much disinformation and fake news), disabled news flash notifications on my phone and I've been spending as much time as possible either sitting outside in the very unseasonably warm weather just enjoying the sun, or curled up on the sofa with the cat and catching up and the gazillion movies I've been amassing to watch. I've also got terrible toothache but the dentists are all closed down in the UK and won't even see people for urgent appointments. My next project is going to be an automatic tooth remover if I can't get this tooth pain under control soon.

Anyway, I've taken a couple of days off work as I had some leave days to burn before the end of the month; though even on leave you are only a phone call away from the next panic. Anyway, I'm in a better place now and from tomorrow for the next 3 days I'm going to try and finish my tic-tac-toe machine. 

I divided the machine into several sections and I've been prototyping each section. I'm hopeful I can get the prototyping completed by the end of the weekend and then I can start on the PCB designs. Not sure how long it will take to get the PCB's made as the manufacturer is in China and they have their own problems right now. Anyway, I really want to get this project completed as it feels like ages since I actually completed a reasonably sized project.
Doing these largish projects brings me a lot of pleasure and it's a great distraction from what's going on. 

So, stay safe and please follow your governments advice about staying at home, social distancing or wherever they are recommending in your area to try and combat this virus. 
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DipTrace PCB software

6/3/2020

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I would just like to thank the people at DipTrace for allowing me to update to a version of their PCB / Schematic software that supports creations with more pins. 

I've been using DipTrace for years and after outgrowing the basic free version, upgraded to a non-profit version that allows my creations up to 1000 pins per design. Over the years this has only once been a bit of a limitation when I designed a large backplane with 10, 96 way connectors plus other components. Fortunately in this instance I could opt for 5 slot boards instead and just connect them together. 

Yesterday however, whilst working on my new tic-tac-toe project, I blew the 1000 pin limit, and not by a small amount either; I'm going to need around 1500 pins (I'm soooo pleased I don't make and drill my own boards any more). Anyway, if you check out the DipTrace website they do offer special pricing discounts for non-profit users. So I sent them a grovelling email, included a link to this website, to the project I'm working on and asked them to show pity on a poor, and basically broke hobbyist... and they came back with a very reasonable upgrade price. I couldn't key my PayPal details in fast enough. 

Couple of things worth mentioning about DipTrace.
I used Eagle many years ago, before they were acquired by Autodesk, and it was an OK product but I personally never took to it. I stumbled across DipTrace when it was mentioned in the electronics mag I used to read at the time and I've never really looked back.
You can do everything you would expect including creating your own parts (which is really easy), and the files it outputs are completely compatible with JLCPCB who I now use to make my PCBs. 

There are some other benefits that I feel are worth a mention.
If I now create a huge board using my new licensing allowances, I can still put a copy of the design file up on my website, and readers can download and open that file using the free version of DipTrace. You can't make any changes to the file if it's metrics exceed your license capabilities, but you can still export the files to send to a PCB manufacturer or print the artwork if you want to etch your own boards. 

The other thing that is very appealing is it's a one off fee. DipTrace offer free updates for minor releases but there's no monthly subscription fees. I'm really not a fan of the subscription model. It may work great for business but I may not get any electronics play time for several months at a time, so and I don't want to be wasting money on a subscription I don't need. I just feel happier knowing I have the original software, and even if the supplier disappears I've got the original installation files and so can still access my own creations whenever I want. 

Would I design a 10 layer PC motherboard in DipTrace; probably not, but that's not what we do; I've only just moved to double sided since I no longer make my own boards. 
So, if you're looking for a friendly but powerful PCB / Schematic design package I'd suggest you to give DipTrace a go. The free version is perfect for even modest creations.

www.DipTrace.Com



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Tic-Tac-Toe

2/3/2020

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I've not been around much and my hobby has taken a bit of a back seat as I've just been so busy with other things. However things seem to have calmed down for now and I've got some time to switch on the soldering iron.

Whilst sorting out my late brothers affects I stumbled across the plans for a tac-tac-toe (noughts and crosses) game that he designed and built in 1978. It was constructed entirely using CMOS logic chips (no CPU or MPU). I remember him working on this project all over Christmas and it being a bit of an anti-climax when it was completed; it's not like you can ever win the game. According to his documentation, it required 188 logic gates spread over 66 separate ICs. It also needed 22 transistors and used LEDs for the square in use indicators and some push buttons allowing the human to enter their move.  Unlike the version of the game referenced in the movie Wargames, the hardware emulation couldn't play itself. The physical version of his game no longer exists.
As a programming exercise I've often written software to play this game when learning a new programming language new CPU/MPU platform, but I've never built one with just logic gates. 
After studying his original plans, it all just seemed overly complex to me. The rules of the game are of course pretty simple with no complex algorithms required and my brother chose to implement the game logic using lots of NOR and NAND gates. He could have done this with a Z80 or 6502 CPU (they were available) but it would have been expensive. It occurred to me that it would be really easy to build a physical version of this game using not much more than a clock, binary counter and some EEPROMS, which lead me to thinking that it could be possible to do this without ANY IC's at all, using just DDL (Diode Diode Logic). There are some problems though using just DDL.
All the logic elements (gates) are constructed using small circuits based on diodes, but each diode causes a small voltage drop that needs to be overcome else after a voltage has passed though a thought DDL gates, the voltage will be too low. Transistors would be the obvious solution but that goes against my pure DDL idea. There would be some research and experimentation required to see if I could get this approach to work, but since I've set my heart on building this game now, I've opted to build an intermediate version using just TTL and diodes.

My idea is to build something that would be familier to anybody who has worked designing Microcode for CPUs. 
There will be a master clock that will supply regular pulses to a counter. The output from the counter is decoded and selects a single row in a matrix. Each row in the matrix represents a rule and if the rule is true, a suitable course of action. 

To keep things simple, my Microcode engine will not support branching. This means that the rule checking starts at the first entry, runs all the way to the last entry, and then just starts again from the start.

The game should allow for either the player or the machine to move first. It needs to check after each move to see if there is a winner or a draw, it needs to make sure the player cannot make an invalid move (cheat) and, if possible, I want the machine to be able to play itself. I will use coloured LEDs to indicate the owner of each of the nine game squares, LEDs will indicate whos turn it is, and the game outcome. Nine push buttons will allow the human to enter their move and there will be a couple of outer buttons allowing the human to setup the game.

First thing I need to do is experiment with constructing AND gates using only diodes. These diode gates needs to be able to interface with the TTL elements. I will also construct some of the major process blocks including the clock, sequence counter, reset and game end logic.

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    A software and hardware engineer who loves retro computers.

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