I've just released new PIC firmware for the PIC Digital Thermometer & Clock project that was originally published on 3rd September 2011.

The display should now run brighter and with less flicker. I also took the opportunity to completely rearrange the internals to make it easier for constructors to make code changes for their own requirements.

I’ve been experimenting with using a PIC to control long chains of 7-segment LED displays, and to find an approach that I can use to replace the obsolete TIL311 displays. To that end, I’ve created a tech article that describes a simple way to do this. My prototype was 24 digits long; long enough for most applications I think, but could be extended. It’s all done with a PIC18F25K22 running from its own internal oscillator, accepts data from a serial device at 9600 baud, and supports 0 to 9, and A to F value display. The code is written in AMICUS18 BASIC which is free so you can change the software to suit your own application. All the fully documented source code is supplied as well as a schematic of the circuit.

The picure above shows 24 digits (6 x 4 digit modules). The display modules each contain a 4 x 7 segment Common Cathode display, a DIL resisor pack on the modules right-hand side, and there are 4 n-channel SMT MOSFETS underneath.
The advantage of using modules on breadboards is the vast amount of time, and wire that's saved. You can throw a quick circuit together in no-time if you already have the modules pre-built. It also saves a lot of breadboard space.

I completed work on a new Nixie Clock at the weekend; this one’s for me. I already had the tubes as I’d bought a batch of 17 off Ebay a while ago and whilst I used 6 for a friend’s clock, the rest were just sitting there begging to be used.

The design is basically the same as the original but I did take the opportunity to update PCBs in a couple of places and add some expansion capabilities.

I’ll be publishing the construction details here soon… watch this space.

I switched on an old computer yesterday. For those in the know, it’s an Acorn BBC Model B from around 1983. Whilst I’ve not had this one from new, I’ve used it plenty of times before.

So, there I am happily playing Galaxians when there is the most revolting smell followed by smoke from the computers underside; the computer did keep running.

Switching off, and removing the lid and it was obvious that the problem was in the switched mode PSU. I also recognised the smell; it’s quite distinctive.

The X2 capacitor that’s connected across the AC mains supply had failed. This is a really common problem in old PSUs.

The capacitor is usually a low value, 0.1uf in this case, and rated for 250v local mains voltage.

Fortunately I keep a small selection of these in my parts bin as it's a common failure and usually only a 5 minute repair once you’ve got the PSU out of the main chassis and dismantled.

Even though the PSU continues to work, this can be a sign that it may be time to overhaul the other capacitors. I removed each of the larger electrolytic capacitors (100uf @ 250v) and checked each one using an ESR & Capacitance meter. They were all well within specification which was good as I don’t have handy replacements for them.
Time to go parts shopping !!

I had to solder one of those retched 16-pin QFN packages recently. The IC in the picture measures 3x3mm

My normal soldering iron bit, which is pretty small, would still be too large for this job.

Manufacturers like to file off the part numbers on IC's to make reverse engineering their products harder, but it also makes reparing an item almost impossible.

A trick that sometimes works is to clean the area with surgical / white spirit, and then place a single drop of water over the component and if you're very lucky, the part number will be visible. You can see from the image on the right that this is a 4017 IC.

My email in-box contained a routine Elektor post email which contains a nice link to download a free Raspberry Pi Wall Poster and it containsa fair amount of useful information.
Funnily enough, it also contains some conflicting information.

The picture shows where the power input cable goes and it states
5VDC / 800mA… which is 100mA more than my Raspberry programming book states. 
However, at the bottom of the poster under “Troubleshooting” it states that it requires a “solid 5V / 1000mA” supply.

It’s a poster guys… it’s not rocket science to make sure the advice is the same across a single page. No wonder people get confused over these things.





You can download the poster here:      
http://www.elektor.com/Uploads/2013/POST/007/Elektor_Raspberry_Pi_Poster.pdf

The replacement metal panels for my old project boxs arrived today. Not a great deal you can say except they have been cut to a much higher standard than I could do in the workshop.

I had some other panels I needed so didn't actually place the order till Sunday afternoon using their website (http://www.clickmetal.co.uk/), and they arrived today; Tuesday, so two days is pretty good service in my book. The panels have a peelable protective coating on one side which is nice. All I have to do is measure and drill the mounting holes and I can then reuse those old, and rather expensive project boxs.

Because of the £10 delivery charge, it makes sense to order everything you need in one go. I think delivery is free if the order value exceeds £200 - but that's a lot of panels.

The larger project cases that you can buy with removal plastic/metal panels can be rather expensive and more often than not, mistakes during machining of the panels or just the retirement of an old project renders the case unusable.

I have three project boxes that have been sitting on the shelf; two of them are identical desktop enclosures and cost around £50 each new. Each has one power connector hole drilled in the back of the case which is fine, but the four aluminium front panels have been extensively worked and are unsalvageable.

So I started looking around for a source of replacement panels and found a company that will custom cut aluminium panels and the price is quite reasonable compared with the price of a new enclosure so I’ve decided to give them a try.

The company web site can be found here: www.clickmetal.co.uk

Each of the more expensive enclosures has two panels, one measures 374x124x2mm and the other 374x60x2mm.

The panels cost £4.00 and £3.18 respectfully from ClickMetal, so around £7 to allow me to reuse a £50 enclosure. Not bad really. I also have another more modest enclosure that uses 2 x 243x70x1.5mm plastic panels. As I use this size enclosure quite often and just to see, I’ve ordered four of these in 1.5mm aluminium.

The total cost for all the panels (eight in total) comes in at £42.77 including VAT and a £9.95 delivery charge.
Orders over £200 are free delivery.

Via their web-site you can get an immediate on-line quote which is rather nice.  I’ll report back on the results.

As it happens, I did find a slightly cheaper company, but they won’t cut panels less than 100mm on a side so not much use for hobbiests.

In 2001 I bought a UV exposure unit for making PCB's from a local supplier. For what it was, it was rather over-priced but to make matters worse, it had a mechanical timer. The results from this were never consistent and I soon learned that exposure time is VERY important.
Several years later I "hacked" the unit and built-in a very basic electronic timer. I was never very happy with it but it did the job; until a couple of months ago when it started acting up.

As with many ad-hoc type projects that you decide to start on a weekend or over the holidays, you have to make do with what parts you have handy, and this was no exception.

I decided over the festive period that I would design a new simple timer unit to replace the current one; I would also add a couple of features that I've come to realise were missing from the original unit.

The one big missing feature is a warm-up timer. This runs the tubes for 5 minutes and allows them to warm up; cold tubes flicker and can affect the quality of the final exposure.
I decided to mount most of the electronics externally to the UV unit for a couple of reasons.

The only transformer I had was a little on the large size and would take up much of the internal free space.

The picture above shows the main PSU and driver PCB mounted. The PCB contains a transformer, 5v regulator, rectifier, and support capacitors. It also contains a relay and driver transistor. This means that ALL the mains stuff is located on this one PCB and mounted securely inside the earthed metal box. At the top left of the picture you can see a small connector that I've mounted. This connects the PSU PCB to the main control box that will be mounted on the top of the unit. There is a cover that fits over the fuse on the PSU PCB that is missing from this picture.
Only three connections are required from the PSU PCB to the control unit; +5v, GND and the relay switch signal.

The above image shows the control box mounted in place.
There is a display that shows exposure time remaining and a beeper to attract attention. The buttons are "STOP" to switch off the UV tubes immediately, "WARMUP" that switches the tubes on for a pre-programmed five minute delay, "INC TIME" to increment the exposure time (in 5 second increments) to a maximum of 300 seconds before re-setting back to 30 seconds, and "GO" to start the exposure and countdown.

I decided to build this as an integrated unit BUT you could build this as a self-contained external device so that you could use it to control the UV unit without any modification. It could also be used as a dark-room exposure timer or any other countdown timer.

At the heart of the electronics is an 18F25K22 PIC programmed in AMICUS BASIC. This means that you can simply change the firmware for your own needs if required.

I'll publish the design for this when I get time.