Sorry for the inconvenience.
At some point, Weebly, the cowboys who host this site, did something that broke all the sites internal links. I've repaired these as best I can but if you do happen to spot anything that's broken, please drop me a line.
Sorry for the inconvenience.
I have a moveable bench light that has two 15w florescent tubes that I've had for several years. A few days ago one of the tubes started flickering and then refused to ignite. They are 18 inches long and I thought I would have a hard time finding them but actually they seemed quite common.
I've had "issues" with buying cheap unbranded long tubes from high street outlets so was a little nervous. I found a place on-line http://www.lampshoponline.com/ and was really surprised at how cheap they were. Because I've had problems before, I bought four branded tubes (£2.48 each) and a couple of replacement starters, just in case.
The tubes I bought were Philips T8 Triphosphor - Colour 865 Daylight which were the same specification as the existing ones - though the original ones seem to be unbranded.
After replacing the one faulty tube and switching on it was like looking into the sun and I couldn't believe how bright the new tube was compared to the other one. I'd never really thought about if tubes fade over time and just assumed they eventually burnt out. Anyway, I replaced the other old tube and I'm very impressed with the amount of light being produced. So I'm guessing the original tubes have been fading over time and I never really noticed.
So, don't know if this was something odd with the old tubes, or if they really should be replaced periodically but I've put a note in my diary to check them next year. Since I bought four and they are probably from the same batch, next year I will replace just one tube with one of my spares and compare the light output.
I received an Email from some kids at Stanford University in the USA about their Kickstarter project for a tool to aid with cutting wires and component leads to the right length when breadboarding.
I's a really nice, simple idea.
You can watch a short video presentation here.
Good luck guys.
I've added breadboard construction details for my bat detector mentioned some time ago. Breadboard documentation software is getting better all the time and after a recent search I found a pretty good one to play with, but it's far from perfect. It's a pig for example to create new parts and whilst the existing library is pretty good but it's by no means complete.
I've been neglecting the site and I apologise for that. Work has been really busy, I got suckered into building a website for somebody (actually suckered isn't correct as I volunteered though I didn't know what I was letting myself in for), and I've been working on some custom gizmo orders for people.
That said I've still had time to play in the workshop and I've got some projects to write-up that I think people may be interested in.
This last week I've been consumed with stepper motors. Well to be specific, trying to find some that are fairly small, powerful and cheap which is proving a challenge.
Ebay is awash right now with 5v steppers that are geared - model number is 28BYJ-48 rated at 5v.
I ordered several but I probably should have grabbed just the one first to experiment with.
Now they are nice steppers for the money. However they have a built in gear box that reduces the speed and means their maximum output speed is very limited. The gear box does mean they have a fair amount of torque though.
They would be great for clocks, robotics and even drive motors as long as you don't want your creation to whizz around the place to fast, but for my application much to slow.
However, they weren't a complete waste. Each motor was supplied with a little driver board. Now I don't use stepper motors often, and I've always opted for dedicated driver chips for them. However these driver boards are simply based around a ULN2003 Darlington driver chip. Each IC's contain seven Darlington drivers, rated at around 500ma and up to 50v. They even have the suppression diodes built in and are perfect for driving low current small steppers, motors, bulbs and relays.
It's one of those "why didn't I think of that" type of situations. You simply drive the IC from your CPU, and with four output lines you can drive the stepper in either direction and run in different stepping modes, all for peanuts. These IC's (or one of the many alternate variants) are usually easy to get hold of, and in the case of the ULN2003, you get three spare driver channels for other things as a bonus. I think there is an 8-channel variant which would be useful for a robot with two steppers.
So, whilst it turned unto a useful exercise after all it doesn't solve my current problem.
One solution that I've tried previously is using a modified radio modellers servo motor.
You open the servo and make a change (usually simple) to allow the shaft continuous 360 degree rotation.
However, whilst usually having masses of torque, servo's are rather large, expensive and quite noisy.
There are some micro servos available but they are tricky to modify for full 360 degree rotation.
So, back to searching Ebay.
I've been sitting on a piece of equipment for a little while and my Christmas project was to get the thing working again, and then make some modifications. It's around 20 years old and it's had a hard life. When it was first plugged in to the mains, nothing happened. After some initial checks of fuses it was time to remove the lid and have a look.
A poke around the PSU showed mains going in, but nothing coming out, There was also some liquid residue on the inside of the case.
Anybody who's played with old equipment will probably have experience of PSU problems - specifically with the capacitors. Over time they break down as they dry out and that can cause all sorts of problems, from low or wandering output voltages, to spectacular bangs and flashes followed by clouds of the most foul smelling smoke.
I pulled the PSU module and inspected the PSB underside. There were signs of corrosion on the board but a quick inspection of the rest of the equipment showed no such damage. This was unlikely to be water damage and so is a pretty good sign that one or more of the electrolytic capacitors have leaked.
The copper side corrosion was also under a bank of three electrolytic capacitors so I pulled them to have a look.
You can see the mess under C12. I've never figured out how the capacitor fluid manages to get through the PCB to attack the underside solder joints and tracks... but it often does. Corroded solder joints on the underside are a good indication that the component has leaked something.
A quick inventory showed there were six electrolytic capacitors on the board. Four of them were 1000uf at 35v. One was a small 100uf at 16v and a big 200uf beast rated at 450v.
This isn't my first time repairing vintage power supplies so I replaced all six. Only the big 450v capacitor could be classed as unusual and I do try and keep a few of these types in the spares box. I also used 105 degree low-impedance types for the 1000uf ones.
However, the other capacitors to consider replacing are the EMI suppression / filter capacitors. These capacitors are usually wired across the Live - Neutral and when they fail often go short circuit leaving a trail of stinky smoke and bits of capacitor housing and fluff all over the place.
Even if these capacitors are still intact, it really is just a matter of time before they fail. They may have already failed open-circuit. They only cost a few pence and take seconds to replace so you may as well do it now whilst you've got the equipment dismantled.
But this failure mode raises an important point.
You MUST replace mains side suppression / filter capacitors with at least the same voltage and X/Y class. The actual capacitance value is usually less important.
The voltage rating should be obvious, but the X/Y class can cause confusion, and getting this wrong can cause a future equipment failure to be fatal.
The circuit above shows a typical basic mains filter / EMI suppression circuit though they can be much more complex of course. It's also common especially in older equipment to find very simple arrangements consisting of nothing more that a single C-X.
Looking at the above circuit, C-X is wired directly across the Live and Neutral, and the C-Y capacitors go from each line to earth.
If C-X was to fail by going open circuit, then there would be no real harm done (other than a loss of effectiveness of the circuit). If it failed by going short circuit a fuse or breaker somewhere back along the power line should blow or trip. Annoying but in the end, no serious harm done.
I've had equipment where the chassis fuse keeps blowing because the X capacitor has failed short-circuit.
If one of the C-Y capacitors were to fail open circuit again, again no real harm done. However, if they were to fail by going short-circuit a situation could arise where the chassis is left at mains voltage.
So typically class Y capacitors are designed to fail by going open circuit.
Of course, an obvious question is why don't they just use Y class capacitors in both applications. It would certainly save a lot of mess and acrid smoke being released.
I suspect the main reason is cost. Y class capacitors tend to be more expensive. A secondary consideration is probably that if a capacitor has failed the suppression characteristics of the circuit have been compromised.
Of course, nothings ever simple and there are sub groups for each of the two capacitor classes and it's important to match or exceed the specification of the faulty one.
Subgroup Peak Service Voltage
X1 > 2,500v and <= 4,000v
X2 <= 2,500v
X3 < 1,200v
Peak Service Voltage is not the components rated working voltage. The working voltage of these capacitors seems to start at around 275V AC so should be more than suitable in domestic mains equipment. X2 capacitors are very common in UK mains equipment.
Subgroup Rated Voltage
Y1 <= 500v
Y2 Between 150v and 300v
Y3 <= 250v
Y4 <= 150v
These capacitors tend to be supplied in rectangular plastic packages that can be soldered flush with the PCB. Once soldered in place, it would be almost impossible to push over without causing permanent and obvious damage to the package unlike regular ceramic disc capacitors.
They also tend to be self-healing and can often recover from a voltage spike, again unlike cheaper ceramic disc capacitors.
Checking the obvious when something doesn't work is of course, well, obvious.
A friend recently asked to me look at a piece of kit that had been giving her trouble. It was intermittent and a swift whack or fiddling with the connections would usually bring it back to life but it had gotten to the point where it was unusable so she had sent it to repair When it arrived back it was completely dead and not wanting to fork out even more money or be without the device for an extended period of time, asked me to have a look.
It's a mains powered device and since UK plugs have a cartridge fuse inside, this is always the first thing to check. Unfortunately the fuse was fine.
I opened the device, couldn't see anything obviously loose or damaged so started checking the continuity of the mains flex from the plug to the device. A-ha. Both the live and neutral were intermittent, so it was probably a break in the cable some place.
I cut the plug off, disconnected the flex from the equipment end, and replaced it. When I came to remove the plug from the old flex to attach to the new one, I found that both the live and neutral screws were really loose. What should have been a five minute repair took around an hour.
Always, always check the simple things first.
On the plus side, the equipment looks nicer with a new piece of black flex rather than the grubby original white one.
I've decided to resurrect my Small Custom Computer (SCC) project again. This will be the fourth time I've kicked this project off... hence it's the MK4. I've got a better handle on what I want from this project and the direction it should take. Hopefully, I'll actually finish this one.
Will it be practical... Not overly.
Will it be blisteringly fast and able to solve many of the problems facing mankind today... Nope
Will it be challenging... Yes
Will it just be useful... As an academic exercise in how not to design your own CPU instruction set, almost certainly.
On the plus side you can build it yourself as a test-bed for experimentation and who knows, it may be a stepping stone for "you" helping to solve many of the problems facing mankind. So, if in the future it does help you in this endeavour, I'd like a mention please :)
In the mean time, you can follow my progress, or lack of here.
I purchased an external 3.5” disk drive enclosure from Ebay the other day which has just arrived. Really cheap and you supply and fit your own drive, but it’s just for moving stuff around so I didn’t want to spend much.
When it arrived my attention was immediately directed to the 3-pin UK mains plug and power lead supplied.
British Standard regulations specify that the earth pin (top pin) should be all metal if the earth is actually needed for the equipment, or can be plastic if the equipment isn’t earthed.
The 50/50 metal/plastic combinations are NOT allowed (left picture) for the Earth pin.
And anyway, as a generic cable it’s supposed to be a standard IEC earthed power cord so should be solid metal.
Also, notice the British Standards mark in the top right corner of the right hand picture... British Standards approved my foot.
This then got me thinking about the cable and connector. The IEC connector has 10A 250V stamped on it but the plug was fitted with a 13A fuse.
In the UK, mains plugs have a cartridge fuse fitted and these fuses are generally available in 3A, 5A and 13A ratings, yet the majority of these IEC cables are rated at 10A. I suspect it's because of the Europeans, however, the lead manufactures know this fact and so use cable that can handle at least 13A... don't they????
When I looked at the actual cable it has 3CX0.75mm2 stamped on it so off I went to the cable manufactures web site.
The below table is an excerpt from one of their data tables.
3Cx0.5mm2 16/0.20 6A
3Cx0.75mm2 24/0.20 9A
3Cx1.0mm2 32/0.20 14A
The manufacturer states that the cable in my lead is capable of carrying 9A. I’m not really happy at that as its well below the 13A rating of the fuse and I would have been happier to see 3C1.0mm2 being used with its 14A capability instead.
However, if the plug can be fake - there's no way that was ever BS approved, could the cable also be fake?
The manufacturer data states that the 3Cx0.75mm2 cable should be made from 24 strands of 0.20mm wire.
I checked the actual cable specified by cutting it in half and it was obvious this wasn’t going to take anywhere near 9A. The actual conductors were made from 30 strands of 0.10 mm wire, and a quick check shows that in fact, this cable is only physically rated for around 1.5A.
The above image shows the fake cable on the left, and a true piece of 32/0.20 rated at 14A on the right.
Now I don’t know about other people, but I tend to grab the power cable that’s closest to hand and “assume” that they are all fit for purpose, but this cable is a disaster waiting to happen.
Be warned !!!
Gabriel, a beginner in electronics, contacted me a few days ago to say he had constructed my PIC Digital Thermometer and clock but was having problems getting the temperature sensors to work.
After some experimentation I managed to reproduce the problem he was having. He'd used DS1820 sensor ICs instead of suggested DS18B20.
I'd never really thought about the differences between the different 1820 IC's, but there are some, and unless you change the firmware for the clock, it won't support the basic DS1820 variant.
This article from Maxim sheds some light on the issue.
Anyway, after switching to a DS18B20 variant, the clock is now fully functional. Well done Gabriel.
The NE555 and all its variants is a basic workhorse for timing and pulse generation applications, and pretty much every hobbyist will end up using one at some point in their adventures.
The only real problem with the 555 is that it’s a bit fiddly to breadboard as there are quite a lot of interconnections to make and it gets really dull and repetitive to keep making the same connections over and over again for projects.
People who read my ramblings will know that I’m an avid user of pre-built modules. They save construction time especially when bread boarding and as you know the module works, they make debugging your projects simpler, so I was pleased when Patrick Grady a high school senior in the US contacted me with this:
It’s small, simple and efficient and I can imagine many beginners would find it useful, either to just experiment with the 555 on its own, or as a building block in a larger project. Since all the hard work is done for you, it will save space on your breadboard and give you more time to concentrate on the rest of your project.
Good luck Patrick.
I've a small notebook computer than is small, light and perfect for carrying around in my backpack. The problem is the external PSU. Whilst it's tiny and rated with a 20v output @ 2A, 9 times out of 10 when I plug it in the 30A breaker in the house that protects the dedicated feed to the workshop trips.
I found an interesting article by Michael Allen of Bear Power Supplies that looks at the PSU inrush problem and some possible solutions.
You can download the PDF of the article below.
The village that I live in may as well be in the middle of the amazon in respect of getting a mobile phone signal. Actually, I bet you get a better signal in the amazon. The problem is my village is in a bit of a dip and the population density just isn't really high enough to warrant better coverage. We are lucky we get broadband (slow but it works) and electricity (it's on more than it's off these days which is nice).
In the UK at least, you can buy active GSM repeaters or signal boosters but they are illegal to use - who said the law was stupid. Several of the mobile networks also have their own devices that they sell but they require power and connection to your personal broadband.
In the good old days I would have just plonked an external aerial on the house and plugged my phone into that, but many modem phones don't have external aerial ports these days. So, what's the answer?
A wave guide!!
A wave guide is a simple arrangement of two aerials connected with a piece of coax. The idea is that that one aerial; usually a beam so it's highly directional and gives a bit of signal gain, located outside, as high as possible and pointing directly at the transmitter, is connected via a piece of the shortest and highest quality coax you can get your paws on to a small suitable indoor aerial. Signals are picked up by the outside aerial, travel down the coax and are re-broadcast by the indoor aerial. The trick is you don't want the aerials to close together that they interfere with each other and since you are not adding any amplification (as it's illegal and would mess up the GSM signal anyway), you need to keep cable runs as short as possible.
I'm really lucky in that a friend gave me most of the bits needed to assemble this wave guide including the outdoor beam aerial, the coax pre-terminated with N-type connectors and a suitable indoor aerial as well.
I decided to re-locate my communications aerial to the back of the workshop so it was as close as possible to where I spend the majority of my time.
The aerial above shows an extension pole, a wide-band communications aerial on the top (white stick), a black GSM aerial mounted on the side that is connected directly to a piece of kit in the workshop, and the main GSM beam aerial; aligned for vertical polarization.
The communications and black GSM aerials are working great.
However, I need to wait for my friend to come over next week with his spectrum analyser so we can align the main beam aerial. The aerial, but it's very nature is highly directional and because of the distance to the cellular base station, being out of alignment by a fraction of a degree will seriously degrade the set-ups performance.
We will plug in the analyser and very slowly scan the aerial left and right till we see a peek on the analyser at the correct frequency for O2 then lock down all the bolts.
What could possibly go wrong.
Once it's all up and aligned I'll report back on it's performance.
I've been really busy and Electronics time has been a bit limited, that said, I'm always eager to undertake projects that assist my work colleagues in their day-to-day tasks.
The organisation I work for have a pretty large fleet of vehicles based at 70 odd locations around a city. The vehicles are fitted with computing and other electronic gadgetry and so when vehicles are not on the road they are “supposed” to be parked at their base and connected to a vehicle charger, which is basically a 12v battery charger with a long cable and connector attached.
During an impromptu conversation around the coffee machine, it came to light that many of these charger units probably don’t work for one reason or another and there is no way of quickly testing them. There have also been problems with some of the vehicle charging ports wired incorrectly or simply having blown fuses, and I made a throw-away type comment that why don’t they have a simple gizmo that connects between the charger and the vehicle and can test the charger output voltage and the polarities. I love that glazed look that proceeds the “wow… can you do that”. Of course I can… I’m an engineer. Luckily, the fleet guy happened to have a charger drop cable handy with a connector fitted and from that I managed to find a suitable socket that would fit. So, using what I had available in the home workshop I designed and constructed a simple tester device prototype for them in an afternoon.
It had to be simple to use as the people using these aren’t really technically minded. It also had to be relatively cheap and strong as devices like this don’t tend to last long in busy workshops.
The pictures below show the case marked out for drilling, the underside of the assembled and mounted PCB, and the finished prototype device.
The drop cable from the charger plugs into the base of the unit, and the fly cable out of the tester plugs into the vehicle.
If either the vehicle or charger polarity is incorrect, the associated LED lights red. If both polarities are correct the charger voltage is displayed on the LEDs on the left; 13v or higher is “good enough”.
The operator can then press the “Load Test” button which simply connects the charger to the vehicle allowing the operator to see the on-charge voltage, and as long as it stays in the green, everything is ok.
If either polarity is incorrect; as indicated by the polarity LEDs, or either of the polarity LEDs don’t light at all; indicating no voltage present, an interlock disables the Load Test function. This is to prevent shorting the charger out if there is fault somewhere on the vehicle.
If readers are interested I’ll post the schematic and PCB foil but there’s nothing clever in this device. An LM3914 drives the 10 voltage output LEDs and the polarity indication is simply two red/green bi-colour LEDs. The only bit of any real interest was the interlock that prevents the Load Test button from working if there is a fault condition, but this is simple enough and makes use of a transistor and relay.
The one thing I was keen on was to reduce the amount of interconnect wiring to a minimum as whilst this was a fun little project and may have earned me some brownie-points with the management, it occurred to me they may ask me to create another 70 devices; one for each location, and that’s a lot of cases to drill and wiring to solder, hence my eagerness to reduce the amount of internal wiring to a minimum.
As often happens with prototypes, it was decided to change the voltage measurement scale to start from 11v and not 10v, which now means the Green band starts at 14v - thank heavens for trip-pots. You can see I drilled a little hole in the PCB so I can adjust it even when the PCB is mounted.
I’ve always thought that resellers allowing purchasers to leave product reviews and feedback was a good idea, and on many occasions I’ve read the reviews and used this to bias my purchasing decisions.
But what happens if the reviews are false, or the company doesn’t actually publish all reviews?
Screwfix in the UK are an example of an excellent supplier who don’t appear to overly sensor their reviews. Yes, they tend to show the more favourable reviews first, but all the reviews are there if you choose to scroll through them and I personally think this works in their favour.
I was looking for a table saw to do a couple of light weight jobs. I could have opted for the cheapest one that was available but after reading the reviews decided that I would spend a few extra pounds on a slightly better model. Win-win… I get a saw that many people seem to feel is adequate for the job, and Screwfix make a bit more money out of me. I’m also a happy buyer now and will return next time I need something. I feel I can trust them.
Unfortunately not all companies are as enlightened, and I’ve now been bitten twice by companies possibly withholding bad reviews, and I know they withhold reviews as they have withheld ones that I’ve written.
I recently bought a wood working lathe. I decided on the model based on the three glowing reviews published about how easy it was to change the spindle speed, and how powerful the motor was. What they didn’t mention was the fact that you needed a socket set to loosen four bolts to change the belt position (changing spindle speed is a common requirement with wood working), and the motor was severely underrated. Also the main components were cheap cast pig iron, poorly finished so didn’t move well.
Needless to say, my less than glowing review didn’t make the list.
I also came foul of this with one of my electronics suppliers when I purchased a cheap-ish RF generator. It boasted a fine adjustment frequency control and ease of range selection. However fine adjustment was impossible as the slightest touch of the cheap single-turn potentiometer caused massive frequency change, and the six band range selector switch, which is actually a twelve way rotary switch without any stops, causes very strange behaviour if one of the unallocated six positions is selected. Apparently this reputable supplier didn’t like these comments either and refused to publish the review.
Not publishing poor reviews is a very silly mistake in my opinion. If I read poor reviews I tend to move up to a more expensive models; I’m a firm believer in you get what you pay for and don’t mind spending a bit extra if it’s going to be decent quality. However, for these suppliers they have damaged their reputation with me. Bottom line… I don’t trust them to tell the whole truth any more.
So, the reseller of the lathe now has their never ending train of marketing Emails automatically consigned to my junk folder, and I refuse to trust my electronics supplier when it comes to expensive items of test equipment.
Read the reviews and then checkout other comparable products being offered by the same supplier. If nobody is ever saying anything bad especially on the cheaper offerings, I’d be suspicious.
Also, check out the reviews for the same product from other suppliers if possible.
I was looking at designing a variable speed controller for the motor on my woodturning lathe. Nothing is ever simple.
Whilst doing some research I came across an article by Kevin Brady who explains in clear and digestible detail, all about Horsepower, watts and amps ratings of AC motors, and the complete pack of lies that some sales and marketing people try to dump on us when it comes to claims about how powerful the motors in their gizmos are.
It's well worth a read.
Happy New Year (to those that celebrate it).
As my first mini project of the year (and to give myself something to fiddle with over Christmas), I've released a small upgrade to the LED clock project I published last October.
By changing the PIC firmware and using this alternate display board, the clock can be turned into a basic Binary clock. Details can be found here.
The battery pack manufacturers are, in my humble opinion, scamming the general public into buying expensive battery packs when they don’t need to.
I’ve a Fujitsu Laptop that I use in spurts. Sometimes it’s in daily use being lugged around with me constantly, other times it gets left on the table under a pile of paperwork and not used for weeks at a time.
Recently I switched it on and the battery was flat and then found that it refused to charge. It’s around four years old so I thought that it had probably just come to the end of its life. The Laptop kept saying it was 98% charged but the charge indicator wasn’t illuminating.
I wondered if perhaps just one of the cells in the pack had failed (and the others could be useful for other things) but then I had a thought; I’ve seen this before with other so called “smart” battery packs. I took out my trusty Dremel power tool and carefully cut into the pack where I suspected the intelligent battery monitoring circuit was.
Once I’d cut into it, I could see the two connections going to the cells and placed a volt meter across them. The pack was reading 9.1v.
I set by bench top PSU to 11v and hooked it directly across the terminals. I applied power for around 5 seconds, removed it, waited a few seconds and repeated a few times. After each cycle I would check the pack voltage and slowly it started to climb. Once I got the pack up to around 10v, I quickly inserted it back into the laptop and switching on the power. Hey presto, after a couple of seconds the charge indicator came on and Windows reported the pack was 4% charged… and charging. I left it charging whilst I got on with other activities keeping a fairly close eye on things (these retched batteries have a habit of catching fire) and after around 90 minutes or so, Windows reported the pack was fully charged and this was confirmed by switching off the mains power and the laptop happily running on its battery pack whilst reporting around 90 minutes of run time available. This is about right for this laptop.
Hindsight is a wonderful thing sometimes. Like may people, I've designed and built projects only to realise; usually when it's too late, that some slight changes or "tweaks" would have been of benefit to the project.
One of these projects is the breadboard PSU. A slight change to the PCB foil layout frees up some additional space on the breadboard. I've just updated the download file for this project with an additional PCB foil.
Another project that I'm in the process of updating is my recent LED clock. I realised after construction that there were a couple of unused I/O pins on the PIC that could be very useful if they were brought out to one of the connectors. There were some other design improvements that became obvious once I started looking at other things I could do with the project.
Of course, a lot of these types of issues are because as hobbyists we don't peer review our designs. At work, all hardware and software projects are looked over by somebody else on the team; a form of sanity check, and it's amazing how a fresh pair of eyes can spot obvious omissions and mistakes.
Now it's not often that I see a piece of tech that makes the hairs on the back of my neck stand on end, but when my friend Max Maxfield send me the link below, that's exactly what happened.
It's called Pixy, and I really really want one.
Read the full article and watch the demo video here:
They have it connected to an Arduino but no reason why you can't drive this from a PIC, Raspberry or anything else for that matter.
I've got a thing for clocks... I wonder if it's because I'm not getting any younger.
Anyway, I had a day free over the weekend and decided It was clock building time.
There's not much to this clock really. A PIC18F25K22 running some simple firmware written in AMICUS18 BASIC. There's a Dallas DS1302 RTC chip with battery backup, and a handful of other components.
I've been experimenting with different firmware to see which makes the display the most readable.
The image on the left of the clock front is showing a time of 10:20:13
I've created a construction project for this clock which can be found here.
Futurelearn are offering free training places on short part-time courses. There’s a limited list to choose from but one that may interest the readers is an introductory course on Java programming.
The courses are run by leading UK universities, are completely free, and you can study at your pace.
The Java course starts early 2014, runs for 7 weeks and they suggest you will need to study around 3 hours per week – that should give me something to do on the train every day.
Full details and a list can be found here: https://www.futurelearn.com/courses
Whilst attempting to repair a simple microphone pre-amplifier for a friend, the culprit was found to be a blown transistor. A quick internet search found the specifications of the device and it was then a simple matter to find a suitable replacement from what was available in the junk box.
Interestingly, my friend, who has only a casual interest in electronics, was bemused by all the Vcb, Vce, Ic and other details in the parameter tables.
So I did a quick drawing of a simple common emitter amplifier based on a NPN transistor and explained the different values.
Below is a sample specifications table for some NPN transistors. Notice the three BC107 transistors at the bottom of the list are from two different manufacturers, but their specifications vary quite a bit. For example, the Hfe (Small Signal Gain) of the TRU device is over four times that of the CDIL variant, but the CDIL variant has a higher maximum working frequency.
The parameter that most hobbyists are concerned about tends to be the Ic. This is the maximum current that the transistor can drive when a load is connected between the Collector and +Vcc.
I've been a bit lax recently and whilst I've got piles of content that I need to complete and upload, pressures of starting a new job are taking their toll. I'm hoping that normal service will be resumed soon.
Anyway, I've uploaded an article (PDF document) that attempts to give the reader a brief introduction to shift registers. Theory is all well and good so there are some simple construction details for a PIC based project that can control up to 255 x seven-segment displays. All the source code and diagrams etc are supplied so the constructor can change the firmware to fit their own requirements.
UPDATE 20th Sept, 2013.... Just uploaded the correct version of the PDF file... sorry about that.
A software and hardware engineer who loves retro computers.