Lots going on with this project right now, but I thought I'd do just a very quick update.
Another batch of PCBs arrived a couple of days ago and I'm slowly working my way through assembling them.

The one thing I've very happy with is that by replacing the relatively slow (in terms of access speed) EPROM that contains the Monitor firmware with an ATMEL EEPROM, I've managed to run the system including backplane and a couple of expansion cards up to 8MHz. The EEPROM is rated at 120ns which is around 8.3MHz.
The CPU is spec'd to around 14MHz so that would require memory and EEPROM with an access speed of around 70ns. This maybe pushing it for an EEPROM so some research on what's available is required.

However, running at 8MHz my SAD (Segment Address Decoder) board, and new 8-LED display board all worked fine. 

Last week I'd had enough of that Dataman programmer. It would sometimes work but more often that not Windows would fail to recognise the programmer. I'd tried it on Windows XP and three different Windows 10 machines (one was a brand new out the box machine) and it was always the same. So I sent their tech support people an Email saying fix it, or they were getting it back. I got a lovely immediate reply suggesting I download the latest software from their site, which I did (even though the version I had was only two weeks old), and hey-presto, problem sorted. Have used the programmer several times and it's worked perfectly each time. 

I've also been working on my Acorn System 1 storage expansion card; and I needed a working EPROM/EEPROM programmer so I could flash an EEPROM that contains the boards memory map.

Whilst it looks like just a jumble of wires, it does work, so far, and I'm rather proud of it.
The CPU simulator on the right is designed to allow me to wiggle all the Address, Data and Control signals. It makes it really easy to set up known signal patterns to a project under test, and then poke around with a scope lead and see what's going on. It connects to the breadboard via a ribbon cable which can be removed, allowing the project to be hooked to a special expansion card that plugs into the computers backplane. 
There will be a full breakdown of how this board works (assuming it does work) soon, but in brief the board contains RAM and EEPROM which are both broken into pages. When completed the card will occupy around 56K of space in the memory map, but will contain around 8Mb of EEPROM/RAM that can be brought in and out of the map as pages.
The two, two digit LED displays on the left show the page numbers for the RAM and EEPROM. The Two digit display at the tope of the board shows the offset that is applied to the memory to allow access to the right page.
All the buffering and decoding logic, as well as some debugging displays/leds etc are on that breadboard including a flash memory that is used to calculate the offsets into the EEPROM/RAMs. The only two components that are missing are the actual EEPROM and RAM chips. They get added next and then I'll find out if this actually works. 

I'm sort or regretting buying this Dataman programmer. I need to spend a lot more time trying to figure out exactly what's going on with it, but assuming my unit doesn't have some weird intermittent fault, then the quality of the software; specifically the USB driver sucks. 
I've tried this programmer now in three different machines; 2 x Windows 10 and 1 x XP SP3 and in all machines it's very hit if the USB driver will work. There seems to be a correct start-up sequence that's required but I can't quite seem to pin it down. I'm hoping to spend some dedicated time with it over the weekend and if I can't get to the bottom of what's going on, I'll have to return it (and I knew I should have kept the flippin box). Bugger. 

Progress on my Acorn System 1 is a bit more positive.
I received a batch of PCB's from JLC the other day and I've started assembling and testing them.
Unfortunately I've already spotted some silly mistakes and areas for improvement.
Of the three I've tested two are fine; with only some slight modifications, and the 3rd which is the backplane board, well, that's for the bin unfortunately.
Somehow, I'd managed to misalign the Euro sockets. The first socket is fine, but as you move along the row of sockets, a very slight position error can be seen and by the 3rd socket, it's impossible to get it to align correctly with the mounting holes on the rack.
The board is still useable standalone, or even in a homemade enclosure, but it's useless if you want to mount in within a proper 19" rack with pre-drilled backplane mounting strips.
So I'm more annoyed about the time wasted than the actual money; a set of five of these boards (minimum quantity) only cost me around £10. 
However, it does give me the opportunity to make some other adjustments. One thing I may do is look at moving it to a single sided board. This will make removing of these large 96 way Euro connectors a LOT easier. It's basically impossible with through-plated holes.

Today, I'm also taking my RSGB foundation exam which will allow me to have a radio amateur call sign and operate a modestly powered transceiver. This should be interesting. I have looked at the syllabus; maybe twice so we shall see how it goes. Twenty six questions, and a minimum pass mark of nineteen required.

One of my ongoing projects is building a replica Acorn System 1 computer and this has required programming EPROMS. Programming EPROMS in itself is fast, but erasing them ready for re-use is time consuming.

So for this project I decided to use EEPROMS. Ebay had numerous Chinese sellers listing all types of devices from 2K to 64K and I bought a selection of AT28C16 (2K x 8) and AT28C64 (8K x 8)

I opted to use an 8K version initially as that fitted my IC socket on my development machine. 
I've documented the problems I've been having with getting that machine to run, and as one options to try and sort out my problems, I decided to abandon the EEPEOMs in case they were causing some weird incompatibility issues. To be fair I've not really got much experience with EEPROMs so it was possible there was some "got-ya" I wasn't aware of, so back to trusty (but slow development cycle) EPROMs seemed sensible for now.

This however meant using my crappy slow EPROM programmer. It's a serial programmer, running at 1200 baud and the software is so old that it would only run (just) on an old Windows XP laptop. It was a real pain.
And this problem has gotten in my way several times.

When my brother passed I kept his Stag EPROM programmer. This is a nice machine but again the software is really only and won't run on a modern PC. I did think about writing new software but who has the time.

I decided to bite the bullet and buy a new programmer that could program anything from a 2716 up.
It really isn't as easy finding a device as it sounds.

Forget all the Chinese ones. All their claims about being able to program anything are a little over hyped when you actually check the supported device list. None will program the 2716 or any device that needs over 18v for the Vpp.

I couldn't find any second had programmers and every google search kept sending me to Dataman who seem to be the only game in town these days. As a kid I'd always wanted a Dataman programmer; specifically an S4 machine, but they were wayyyy to expensive for me.

A few days ago a brand new Dataman Pro-40 landed on my door step. We won't discuss how much it cost, but I'm on bread and water for the next month.
That said, you get what you pay for.
I did have some weird problems installing the USB drivers on both of my Windows 10 machines but a couple of days later the problem just cleared itself and everything has been fine since. I'm wondering if there were background Windows updates being downloaded.

The Windows software is nice and easy to use and it's tee little things that make it a pleasure to use.
The software's all in English for one thing. Quite often if you do something; program or verify device it was ask if you want to do it again making it a lot faster to process many devices quickly one after the other. In fact, they have added a "YES" button to the actual programmer. Old chip out, new chip in, set the locking leaver and press the button on the device and the software just runs again. It makes it really quick especially when checking ICs.

This leads me onto the fake Chinese EEPROMS I'd bought.
The Pro-40 will also test jelly bean type logic ICs and memories. 
I'd used it to test my stack of 6116 memories and was pleasantly surprised to find only one out of around 20 was faulty. I've had them in my junk box for years so I was actually amazed at this result. 

I tested the ten AT28C64's I'd bought and one of them was found to be faulty. Interestingly it was the one device that I'd been using in my development system. The other nine IC's were fine.

I then tested the ten AT28C16's I'd bought. Nine of them were faulty. By the time I'd finished I could spot which were the fakes and I left the one I thought might be real to the end and that's the only one that passed.
Again, you get what you pay for I suppose... though I didn't pay good money for a box of fake/faulty chips. I wouldn't have mined so much if a couple had been faulty, but only one out of ten... I think that's taking the micky.

I've been working on building a replica of an Acorn System 1 machine for quite some time and it's basically been working, but had a really annoying niggle that I've been struggling to fix. Anyway, yesterday I was browsing an online forum and decided to post details about the problem I was having. Talk about a long shot.
It took an hour or so for somebody to reply with a suggestion, and they were spot on.
Took me ten minutes with a scalpel and soldering iron to cut and bridge a couple of tracks and hey-presto, it sprang into life and works perfectly.

So, I now have a fully functional System 1 CPU board and keypad/display.
There are some updates I need to do to the PCB foils and the schematics to reflect the fix and add some additional ideas I've thought of, and then I'll put all the design files up on this site for those that want to build their own.

For those that know the Acorn System 1, there are a few changes in my version that should make building this one a little easier, but will also make it not completely compatible with existing Acorn hardware setups.

Whilst it does make use of the old bubble style LED display, there is provision to add a larger LED display as I've routed power to the display connector. I will have a design for a powered LED display soon.

It makes use of the W65C02 CPU instead of the older 6502. This gives some additional features including the ability to single step the CPU for debugging, and it will run at speeds much faster than the 6502 which was limited to 1 or 2MHz depending. Actually it will run at any speed from DC to around 14MHz in fact and it's useful to be able to run it at a very slow speed for debugging. 

The edgeway connector is different to the original. Mine uses a 96 position Euro connector with columns A+C loaded giving 64 pins, and whilst I did generally follow the original Acorn layout there are a couple of differences and some additional pins used. This means that the board probably won't be plug-and-play into an original Acorn existing rack system or be pin compatible with Acorn expansion boards. 

There is a more flexible clock oscillator circuit which can make use of any crystal up to 16MHz and divide down to the 1MHz required if you want full compatibility. This will save the having to source an expensive 1MHz crystal; assuming you can find one.

Instead of the two small PROMS on the original, only the EPROM socket is provided and this has been modified to accept the more common and simpler to program 2764 instead of the 2716. Many of the cheap EPROM programmers won't program 2716's. It will also work with an 2764 EEPROM.

The 2 x 2114 RAM chips have been replaced with a single 6116 RAM chip.
This also gives you 2K instead of 1K of RAM (this is configurable with a jumper).
(I will be changing this to use a more common RAM chip.)

The next step is to find a suitable workaround for the last component that is really difficult to find; the INS8514. I'm lucky in that I have one but they are really hard to find and very expensive. They are also quite easy to damage and without one, you can't get the display or keypad working. I've got some ideas for this.

The cassette interface has been removed. There is provision for a plug in card to be added to the keypad as all the control signals are still present if you really do want a cassette interface, but I think in these modern times, we can do better than magnetic tape. That's a future project.

The main PCB has been modified to take a standard euro PCB connector for mounting in a rack. Also, the keypad/display is now connected via a 20 way ribbon connector with ICD connectors at each end. This means you can remove the keypad if desired without having to desolder/resolder the ribbon cable. 

There's also a power on LED on the main PCB and provision for a reset switch. The keypad also has a reset switch and also has the IRQ and NMI buttons.

As long as it's set to a 1MHz clock rate, none of the above changes should break compatibility with an original System 1; with the exception of the cassette interface and that can be added if required, so it should be able to run all the original software.

As with the original there are no surface mount components and provision is made to socket all the ICs. Whilst there is a fair amount of soldering required to assemble one of these, it should be relatively easy for some somebody with only limited soldering experience. The hardest part is probably making the 20-way keypad ribbon cable. 

Once the plans are fully updated and I've checked to make sure the new PCB designs work as expected, I'll post something here in my blog.

I'd started to think I would never get this working so I've really very very pleased it's now running as expected.

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. 

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

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.

So, as always I need to apologise for neglecting things on the site but I've just been so busy. Besides being busy at work I've also been busy in the workshop. One project that I'd like to share with you is my attempt to re-create an iconic British 8-bit computer; the Acorn System 1. 
The Wiki for this computer is here: https://en.wikipedia.org/wiki/Acorn_System_1

By todays standards, the Acorn System 1 was probably less powerful than a modern calculator with only a very limited amount of RAM (just over 1K on board) and a clock speed of around 1MHz, but for many people in the 1970's this would be an introduction to computers that would send them off on a journey that, hopefully, is still ongoing for them today. 

I wasn't rich enough to possess one of these beasts, but my brother was, and it has always held a certain fascination for me. I would see him slaving over the keypad for hours at end, with the result being a few flashing LEDs or some terrible sounding music coming from a tiny loudspeaker he'd connected to the thing. Even so, it was the most fascinating thing I'd ever seen and that wonder has stuck with me all these years. We will return to this in a minute.

A few months ago, I discovered JLCPCB. I used to create my own PCB's but they were limited. Typically single sided and whilst you can do some really clever things making your own boards, there are just some things that are too difficult. To be able to have double sided, high quality boards with a silk screen always seemed like a very expensive luxury. I'm going to create an article on getting PCB's made with JLCPCB. Long story short for now, I needed to order some PCB's and though since I'm paying for postage, is there anything else I want. It was at that point that the Acorn System 1 popped into my head and I decided to slip some PCB's that could, in theory, allow me to re-create the computer onto the order. This was a rush decision. I needed to order the original PCBs ASAP as I had a time critical job that was waiting for them, so I gave myself 24hrs to design a set of PCBs for the Acorn.

I had some hi-res pictures of the System 1 boards, and circuit diagrams, but the pictures were only of populated boards so you can't see all the tracks and their end points and I did find some discrepancies between the board pictures and the circuit diagrams. Also, the Acorn System 1 as was, uses some chips that are not exactly modern these days, and one (or two depending on the final configuration) are all but impossible to get hold of. I will cover exactly how, what and why I did to get the PCBs created in a separate article, but suffice to say for this blog entry, the PCB's arrived yesterday. 

JLCPCB have a minimum qty of 5 boards for each design, which on the one had seems a bit wasteful; especially since I don't even know if my design will work, BUT the boards are so darn cheap you don't really need to worry.

So, the above picture shows the boards and the partially assembled Keypad / display board. 

I wonder if this will work. 

The last 12 months have been hectic and my hobby has suffered as a result. However, things are "hopefully" starting to calm down now and I can return to my beloved pastime. 

I always book vacation time over Christmas and as it's a nice block of time, that's when I undertake my Christmas project. I did have something in mind for this year, but as usual, events overtook me.

Long story short, I made a new friend Dennis, and Dennis has a hearing problem. Whilst we were chatting he mentioned that for various reasons he didn't want to use a commercial hearing aid, so he'd tried to assemble one for himself using an off-the-shelf headphone amplifier but it wasn't really working. After inspection and a little test, the reason became obvious. It was designed for line-level audio input and not direct connection to a microphone. 

Now I could just have added a pre-amplifier, but even then the performance wasn't going to be great. Since size isn't too much of a problem, it occurred to me that some of the available space could be used for adding some audio filters. This opened a complete can of worms.

Depending on the listeners situation, the filter requirements are going to be different. Maybe you're just wanting to enhance the speech audio from someone you are talking too face to face. Or maybe you want to filter out some background noise. Maybe you are at the opera and want to enhance the vocal range but subdue the music from the orchestra and it soon became apparent that this is the sort of project you can make as simple or complex as you want. 

So, some type of adjustable filter would be required. A band-pass filter would probably be ideal. This would allow frequencies within a certain range to pass through, but attenuate frequencies that are either too high, or too low. To make it truly configurable, you need to be able to adjust the lower minimum frequency, and the upper maximum frequency thus leaving the pass frequency range or pass band in the middle.

Something with a preamplifier, band-pass filter, and headphone audio amplifier in a box with a rechargeable power source seems like it would do the job nicely. But how to design and test a suitable filter design.

I don't have any equipment that I can easily utilise to measure the performance or profile audio filters. My spectrum analyser has a sweep generator built it, so this is ideal... but it only works down to around 30 KHz which is wayyy too high for audio work. I need something that will go from near DC (0 Hz) to around 20 KHz.
I need an audio spectrum analyser; or Audio Analyser as they are called. They exist, and you can buy them, but when I saw the price I thought bugger that, I'll make my own. 

The process to profile or measure the response characteristics of a filter is pretty simple. Inject a signal of a known frequency and amplitude into the filter input, and measure the amplitude at the output. Repeat that for a selection of frequencies from the filters minimum to maximum frequency range, record the results, plot them on a piece of graph paper and hey-presto, you get the filter profile, and yes, I "could" do it that way. But it's very labour intensive and if you are want to tweak your filter design and re-profile it, it starts getting very time consuming. What's needed is a gizmo to do the hard work for you. 

More soon...