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...

I like 19" card racks. I've made use of 19" racks in several projects including a custom computer and an extendable bench power supply unit. The only real problem with them is cost.
The basic 19" frame is reasonable enough, but the card front panels and some of the other bits are really expensive.

So, several months ago I purchased a 3D printer kit. Historically I've been really unlucky with CNC machines and they have always been more trouble than they are worth. However, I've been wanting a 3D printer for ages and I've been really looking forward to being able to print some custom parts including these PCB mounts for my 19" racks.

These plastic parts are used to mount the PCB to the card front panel, and I'm amazed at how much they cost; talk about daylight robbery. So, after a lot of fiddling and experimentation, I managed to print a reasonably accurate version of the above. It even worked and this then got me thinking if it would be possible to print the front card panels as well.

A couple of cards in my extendable bench Power Supply

So, after some hacking around in Microsoft 3D builder (which is a really primitive 3D building tool but does the job) I created a model that prints a front plate with integrated PCB card mount bracket.

The next step is to print the front with all the holes pre-made for the switches and LEDs etc. It will save a small fortune in buying metal front plates, and a lot of time in prototyping and building as there should be no more drilling and endless hours at the bench with a file trying to make pretty square cut-outs for displays. 

The digital thermometer clock has been a real success. Many people have contacted me to say they've built it successfully; most of those people had no issues in construction. However, the performance of the clock; mainly it's long term accuracy has been an issue. The DS1307 RTC chip was good (and cheap at the time), but it's not great in a clock like this and constantly seems to need adjusting.

A little while ago I stumbled on EBay suppliers selling DS3231 modules for around £1.50 each for a complete module so I purchased a couple to experiment with and see how easy they are to use.

Today I upgraded my clock to use that module. A little bit of fiddling with the original PCB is required but it can adapted relatively easily. A few changes were also required to the clocks original firmware.

Anyway it's been running on the bench for a couple of hours without any problem, so I'll publish upgrade details soon. I'm also going to re-publish an updated version of the original design.

Details on how to update the original design can be found here.

I've written a review about these buck voltage regulator modules that Ebay is awash with.
You can read it here.
I won't spoil the surprise by giving you the ending.

This was one of those projects that should have taken an afternoon and didn't, however it's now complete and working rather nicely.

I already had a box from a defunct project that had the 4x20 LCD display installed and power switch, mains transformer and a mains IEC socket on the rear so I decided to re-task it for this.

Inside is a PIC18F25K22 running this show, and the device can monitor up to three channels. Each channel has a 5-pin din connector and cable that connects to a Maxim DS18B20 temperature sensor.
You can set the alarm temperature independently on each channel, and the project starts beeping and flashing the LCD backlight if a maximum is exceeded. I also included a relay that can be used as a power interrupter for the project under test. This way I can leave a project on soak but if it starts to over heat, the power can be cut automatically.

The reason it took longer than anticipated was for some reason the PCB never etched correctly and I had some messing around to do. The software only took around an hour to write and debug. I love Proton BASIC.

...and the reason it's three channels and not more, well I happened to have three 5-pin din sockets in my junk box. If I'd had more... who knows.

If anybody is interested I'll make available the circuit diagram, PCB foil and PIC firmware but this really is an easy project to design and build.

So, now that's up and running, I can get back to the original task of designing a decent voltage boost converter.

So, over the last few evenings I've managed to finish the first useful board for my new extendable PSU; a 5v board that can supply around 3 amps. It has a trim control that allows the output to be adjusted from 5v to 6v, and two op-amps wired as voltage comparators that illuminate a couple of LEDs to indicate over or under voltage conditions (less than 5v or more than 6v).

Now all happy that I'd got my first board up and working I set about designing the next one that can provide a variable 0 to 30v at around 1 amp.
Happily playing with some ideas on my breadboard I suddenly noticed smoke coming from the circuit, a bang, and then a piece of the voltage regulator went flying past my head.

The problem was, besides a fault in my design, I hadn't noticed that the regulator was starting to fry.
I did have an amp meter in series with the board but I didn't see what it was reading.

What's needed I thought, is something that can alert me to when things are getting hot.

So, I've started on a new project. It will have the ability to monitor multiple temperature sensors and report audibly if one or more of them exceeds a pre-defined temperature. All this so I can eventually measure and record the discharge curve of a battery pack. See previous blog entries to find out more about that.

That's another breadboard with a half finished prototype put to one side, and the start of another project; multi-temperature sensor alarm project. I need to think of a more snazzy name than that. Whilst it would have just been simpler to pick up some cheap data logger off Ebay.... it wouldn't have been so much fun.

Oh.. and a word of warning. Electronics on the whole is a safe hobby. Baring the old soldering iron burn or stabbed finger when a screw driver slips, you should be pretty safe if you are sensible and carful. However, things do go wrong and most components will complain venomously if they are stressed beyond their design parameters; or just connected the wrong way around. I'm fortunate in that I wear spectacles and they offer a limited amount of eye protection, but you do need to be carful. When things start to go thermonuclear, it usually happens fast. 
If you're ever present when a tantalum capacitor explodes, you will wish you had a gas mask and fire extinguisher handy never mind a pair of spectacles.