Easy Electronics DIY Projects

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Welcome to all my beloved "boys" (and that includes the girls too!) who enjoy doing things.
Together let us get our hands on things and make them better...
... and better-suited to each of us!

Monday, March 20, 2017

EASY RADIO REDUX

Gift of the Magi

Talk of Wise men ... oops! ...persons... bearing gifts?

Well, I too had such an experience --though not in December.

When a younger cousin came to me last month with a smile and proferring a packet, asking  me to "take a look" when I was free, I never had an idea what I was letting myself in for. That was how the old, battered transistor radio migrated to my table. Opening the package that weekend, I discovered a cute little AM/FM box that had seen better days, but which clearly was a treasured friend, especially on busy mornings when radios regulated the schedules of busy people rushing "to beat the clock".

Opening the small cabinet turned out to be a big task, even with a generous spraying of that wonder formula WD-40 and application of muscle power. Months (years?) of being forgotten at the back of some damp cupboard had invited rust and corrosion. Somebody had left the old batteries in, which had leaked and corroded the innards.

The rusty innards...
The printed circuit board, all the switches, and even the little speaker was rusted and corroded. It was a total write-off. My cousin's face fell. Her fond hope was for it to be given just a wee bit of life so that it will produce some nostalgic sounds once again... But, alas!


Operation...

On a whim, I removed all the old junk and cleaned up the cabinet at the kitchen sink, and stood the now pristine looking cabinet on the shelf--for inspiration! It stayed there for a few days. One evening at the electronics spares shop (another dying breed!) hunting for some parts for my current project, I overheard a couple of young girls enquiring if the radio kit had come. I was all ears as I knew that sources for radio and cassette player spares had dried up long ago.
The FM/USB/SDC player

The shop owner, my old friend, pulled out a few small packets, connected up a couple of AA batteries and Voila! a nifty display came up reading 90.8, and music blared out of the small speaker laid face-up on the counter top. It had a small modern high-density pcb and front panel.
The modern PCB
The gizmo was a stereo FM tuner, a USB and SD card music player, with a small display, an Aux input AND a full-function remote -- all for less than Rs 200! Hook it up to an amp or to a small amp kit (just about Rs 60!), and you were in business. Ah, just what the doctor had ordered! I took home a couple of them without a second thought.

... Success!

With enthusiasm, I set to work. Wonder of all wonders, the old mains transformer and power supply board from the radio was working all right.
Good! That gave me 8-9 V DC. I drilled a few vent holes for the transformer, replaced all the old electrolytics, wired up some 1.5 kpF caps across the rectifiers for noise suppression
The mains power supply
(Radios are particularly sensitive to all sorts of electrical noise, especially when working on a mains power supply. So, for insurance, I added an R-C "snubber" too at the output of the PSU.), added a 5V regualtor for the tuner/player module, and tested it. I had opted for a 1-inch-square mono audio pcb
Typical TBA 820 audio amp
with a TBA820 chip that was okay with supplies up to a maximum of 12 V. All checked out fine.

Now, the ten-lakh rupee question! (No, I'm not comfortable working with millions,in rupees or dollars or Euros!) Where to mount the little player?? A couple of days of staring at the radio finally brought some inspiration. Put it on the top, where the little push buttons would make it look like an old two-in-one cassette player!
The 2-in-1 look
This also would call for minimum "surgery", and did not spoil the "original looks". The old AM/FM bandswitch slot at the back came in handy for mounting the combo on/off/volume control.
Back view - note vent holes
Easy!


Now it was only a matter of wiring up everything neatly,
Note: Be careful while connecting up
cleaning and connecting the telescopic antenna, and closing up the cabinet with new screws!
Playing music from a USB drive

A few hours' work had given a seond lease of life to an old beauty, and that too in a contemporary new digital "avatar"! My cousin's open-mouthed look of disbelief and happiness was more reward than I had anticipated.
Tea table beauty!









Well, wasn't it Shakespeare who said " All is well that ends well"?!!

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Thursday, March 28, 2013

EASY ACRICH RUSH


What, after all, is in a name, you might think. But for us eager beavers the mere mention of the name Acrich was enough to galvanize us to action! The busy, clogged streets leading to our fav spares shop was covered in double quick time. There below the glass of the "show counter" was the large reel pack with the octagonal beauties. Soon with a few pieces in the pocket and no specs in hand, we sped back to the home lab, itching for some "hands-on" experience!

As many of you are sure to know, 'Acrich' is the trade name of a wide range of "direct AC mains" LEDs manufactured by Seoul Semiconductor, a company mentioned often in these pages for the quality LEDs they make.( http://www.seoulsemicon.com/en/html/main/ ) Naturally "direct AC" means that the bother and
expense (not to speak of the reliability issues!) of a 'buck converter driver' circuit to power the LEDs from the mains voltage is eliminated. Another plus point from the hobbyist's angle is the versatility offered by this device. You can adapt almost any mains lamp to hold the Acrich LED as all it needs is a pair of small screw holes for mounting!


Of course, as we all know, any 'hi-lux' LED needs to have enough heat-sinking, but in the case of most lamp assemblies with large metal plates, this is a non-issue as the mount itself could serve as the heat-sink. In a non-metal lamp assembly, you could choose a small heat-sink to fit and then mount the LED onto that. Just solder the two mains wires to the LED base plate solder pads, and you are done! It is as easy as that!!
 After the mandatory "Googling around", we unearthed some facts about the devices in hand. They were AN 3231 types with a power rating of 4 Watts. The colour was warm white (very good for reading lamps) and luminance flux was around 150 plus, and they were rated at 20 mA at 230 Volts. The octagonal insulated base plate carries the four chip LED in the centre, with a couple of surface-mount resistors and capacitors, and of course, the etched wiring for interconnection. Apparently the four LED dies are internally wired in 2x2, series/parallel manner.
Of course, this apparently was one of the "low horsepower" models from Seoul Semi, as they currently produce some very powerful Acrich-2 models with 'on-chip' integrated drive electronics that probably set the standard when it comes to features and performance.(http://www.seoulsemicon.com/en/html/Product/Product_view.asp?catecode=1002001)

Now the iron was hot and it was time to wire up what we had in hand rather than dream of 'super' Acriches. To go with the 'easy' tone of the project, we chose a left-over 5 Watt LED 'bulb' mount from the previous project. This made it easy to provide enough and more heatsinking, and gave us the option of trying it out in
many lamps and fittings. The assembly, as you can see, is ultra simple and easy. Take care to solder the leads to the base plate before it is mounted to the heatsink, as otherwise a small soldering iron may not be able to melt the solder on account of the heatsinking! The trick here is to wait a few moments while the iron gathers up 'heat inertia', and then quickly do one connection. See that you apply the heat to the pad and the wire and let the solder melt fully to give you a shiny joint. Leave the leads long enough, and then after smearing some heatsink compound onto the back of the Acrich base plate, mount it onto the bulb-shaped heatsink. Be sure to have checked out/drilled the holes for mounting and also for the leads. Feed the leads through and solder them to the bulb base. Screw the assembly together, screw on the diffuser, and yes, you are ready for switch on!

All things considered, this sure is a "newbie" project. The simplicity and the versatility of the Acrich device
and its wiring up lends it to being adapted to many uses. We did try three devices in a "ceiling dome" type of lampshade, and the twelve watts of warm white light was indeed bright and pleasant. A few days of living with the new darling revealed a quirk or two, however! As mentioned earlier, these are simple 'direct AC' assemblies, and unlike the current crop of Acrich-2, these lack sophisticated on-chip drive electronics. This means that when the mains voltage dips during peak hours, the luminance also drops a little. But this is no major drawback, and all in all, the project could be recommended to enthusiastic DIYers wanting to "convert to LED" and go 'green'!!

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Sunday, February 10, 2013

EASY CHEAP LED BULBS


Energy conservation is a laudable aim and we are all for it. But when the monthly electricity bills assume the form of a recurring fine, surely our thoughts and efforts accelerate towards achieving some sort of reduction in our energy consumption.

For quite some time we have been "seriously toying" with LEDs and trying to replace as many incandescent bulbs and CFLs with them. Though all the 'ingredients' were available in the hobby market, still our LED lamps remained bulky and somewhat uncouth-looking as compact heat-sinks, drivers etc were not available. Now that situation has been rectified to an extent and let us revisit the LED bulb scenario.


Of late good quality sub-assemblies for LED bulbs have become available in the hobby market at competitive prices. The kit of parts include a bulb-shaped heat-sink assembly, an anodized aluminium LED mounting plate, a diffuser for the LEDs, the switching converter or 'driver' for running the LEDs from the mains, and of course, good quality LEDs at reasonable prices from Seoul Semiconductor. In a previous project we had used Seoul Semi LEDs and now after months of use, we can vouch for their quality and steady light output.

The open market also carries LED bulbs from various known brands, all mostly sourced from China, but coming at a premium price. By going the DIY way, on an average, the hobbyist can save about 30% and have the satisfaction of having built the lamps with her/his own hands using good quality components. The heat-sink assembly is sourced from China, though the drivers are locally made with good quality components. The Seoul Semi LEDs are a bit costlier than their Chinese cousins, but they ARE better and it is best to bet your money on them rather than on some unknown devices. In my case, I was able to garner the parts for a total of about Rs 360 for the 3 Watt version, while the 5 Watt was costlier by about Rs 100 plus. Not  bad deal, all things considered.

Construction couldn't be easier! First off, mount the LEDs (all 1 watt Seoul Semi devices) onto the anodized aluminium mounting disc, observing the correct polarity. The discs are printed with legends, and it is easy even for a novice to follow them. Do apply a thin layer of heat-sink compound on the metal back of the LED before soldering. It is best to tin the pads with a very small quantity of solder beforehand. Clean the soldered disc thoroughly with isopropyl alcohol, as otherwise the residues of flux could lead to corrosion and failure after a year or two. Using three small screws, mount the disc onto the heat-sink, again with a coating of heat-sink compound. Please note that the 3 Watt bulb uses 3 x 1 W devices, while the 5 W has 5 x 1 W LEDs. You may connect up the driver temporarily and briefly touch the +/- leads to the pads on the disc to test that the LEDs light up.

The drivers are constant current switching power supplies and they feed about 300 mA to the LEDs. Mount the appropriate driver into the cavity of the heat-sink after putting in a roll of Kapton or other high temperature plastic sheet (readily available from shops that supply transformer winding wire etc) for insulating the driver from the body.  Feed the red/black wires through the hole in the LED mounting disc and solder them to the + and - pads correctly, again, cleaning up after soldering. Now solder the AC input leads of the driver to the bulb terminals and screw the back firmly onto the heat-sink. Check everything once again and screw on the diffuser. Your LED bulb is ready for service!!

Plug it into a regular lamp holder and you can bask in its cool light confident that your electricity meter is running far slower now! Be a responsible citizen -- save energy, and save some money on the side too!

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Monday, June 25, 2012

EASY DIY HEATSINK

Many DIYers might have had difficulties in procuring suitable heatsinks for the LED spotlight. Here is an easy way out, which solves the problem and affords some added DIY pleasure too!


Look around in the junk or visit the friendly neighbourhood aluminium fabricator and you could carry home offcuts of rectangular section aluminium extrusions. I got a good length of 2.5 x 1.5 inch section used for door frames/partitions etc.

The first step is to cut off two pieces of 2.5 inch length. Mark off the mid point of the 1.5 inch side and make saw cuts, so that you now have four U-shaped pieces. File the lengths of two pieces so that they fit within the channel of the other two pieces. The accompanying photos make the procedure clearer.



Do note that heat dissipation depends on the area of the active surfaces and on air cirulation, and also on the colour of the heatsink-- black radiates best. To help with this, make saw cuts on the sides of the U-channel, and using a pair of big pliers, slightly bend the fins to stagger them. Again, the procedure is made clearer if you refer to the photos.

Assemble the four pieces in the order shown and drill the necessary fixing holes to mate the heatsink to the LED holder. Mine needed three holes and another small hole for the wires. Mark and drill one hole carefully, keeping the alignment of all the pieces. Now clamp them together with a nut and bolt and then drill the remaining holes. De-burr the holes, clean all the pieces so that the surfaces mate closely, and then paint the 'free' surfaces matt black. Now dab some heatsink compound on the mating surfaces and screw the heatsink to the LED holder, carefully passing the wires through its hole.


Your home-brew heatsink may not look 'spic and span', but it surely is a "cool one" when it comes to doing its job well!


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Wednesday, June 6, 2012

EASY LED SPOTLIGHT

# # #  WARNING # # # # # # #  # # #  # # # # # # # #
Eye doctors strongly caution the experimenter/hobbyist against looking directly at a lit LED. The risk of retinal damage is very much there even with low power LEDs on account of their highly focussed and coherent beams emanating from a near-point source. The danger is VERY REAL with higher power LEDs.
The reader is STRONGLY REMINDED of the need to exercise great caution.

The easiest way to ensure eye protection is to fix a small piece of plastic diffuser in front of the LEDs with adhesive tape as the very first step-- I had good results with the speckled plastic that is used to make flexi CD pouches and file folders-- until the assembly is safely fitted into a good diffusing fixture.
# # # # # # # # #  # #  # # # # # # # # # # # # # #

Of late LEDs and LED lights have been, how does one say it, "very much in the spotlight"!

Long service life, reduced power consumption and the plus point of 'going green' were some of the factors that favoured the minuscule semiconductor 'light bulbs'. Increased R&D activity in recent years have raised the bar of Lumens (light output) to higher and higher levels, along with a lessening of costs, so much so that high power LEDs now offered the enterprising hobbyist opportunities for replacing many of the lamps in his/her home with DIY LED lamps.

Seoul Semiconductor (http://www.seoulsemicon.com/en/) is a comparative newcomer in the field, but that has not prevented them from reaching the very cutting edge of the technology in a short time. (The company is an innovator and their latest product 'Acriche' is a case in point. It has no usual --and unreliable-- components like resistors and capacitors and transistors that make up the conventional LED driver, but relies on just a custom IC integrated with the LED chips on a ceramic mount offering DIRECT AC connectivity with NO OTHER driver requirements.) (http://www.seoulsemicon.com/en/product/prd/acriche.asp)

Recently when some higher power yet cheap Seoul Semicon LEDs in the 1W and 2W range came into the market, I thought it was time to wire up a practical spotlight.



Luckily I had an old LED holder and lenses lying about. Many holders (for old 5mm LEDs) and lenses are available in the market and the good thing is that the Seoul Semi LEDs will fit those like a glove.


The 1W LED has a single 'chip', while the 2W one has a couple of chips--easily viewed with a magnifier, NOT when it is lit! The current consumption is of the order of 330 mA and less than 700 mA, respectively. But in the interests of long life, I would opt to operate them at about 320 mA and 630-640 mA, and also mount them on substantial heatsinks for cooling. It is easy to 'spec' the heatsink -- after running for a few hours, one should be able to touch it firmly and keep the finger on the heatsink; anything hotter would be suicidal in the long run.
Unfortunately, suitable round heatsinks with vertical fins (as shown above) are not available in the hobbyist market. But dont despair! A visit to the friendly neighbourhood computer serviceman or the electronic junkyard is sure to yield suitable round or square (just cut off the corners with a hacksaw!) CPU coolers.

This is an 'easy' DIY column, remember! And I found that it was not exactly easy for the average hobbyist to fabricate a mains LED driver. So I opted for an easy solution. The market is flooded with cheap 12V / 1Amp mains 'adapters' of the switching type. Upon opening the plug-pack case, one is presented with a neat, compact SMPS on a 2.5" x 1" pcb.

You need another cheap component-- the LM317 adjustaable voltage regulator from National Semi-- which we will configure as a constant current driver for the LEDs. Be warned that LEDs die an early death if they are operated at currents above their design specs. A simple series resistor might be all right if the driving voltage for the LED is steady as a rock. But any other situation would call for a constant current driver. A couple of small resistors complete the BoM or the Bill of Materials for your spotlight.

Kindly note that here I opted for the 2W LEDs, the holder accommodating three; connected as a series string, they were driven with 620 mA. For a smaller lamp, you could opt for series string of 3 x 1W LEDs (about 320 mA) or if you wanted a 'spread out' light source instead of a spot, for two parallel strings of 3 x 1W LEDs (approx 640 mA).
-----------------------------------------------------------------------------
A  CAVEAT:
I was lucky to get a '12V' SMPS whose output was way above and as a result, the LM317 constant current driver worked all right even with a series string of three LEDs.
Please note that the series string of three LEDs will need about 10V to drive them and the LM317 needs about 2.5 to 3V more than that at its input to work reliably.
If your SMPS outputs just 12 V, it would be best to put two LEDs in series, which need a drive voltage of about 6.6 V and so the 12 V smps should be more than adequate to ensure correct operation.
Do measure voltages and currents with a reliable and accurate muti-meter.
-----------------------------------------------------------------------------
It is easy to set the constant drive current by selecting just one resistor (R) as per your requirement. The LM317 while operating produces a constant 1.25 V between its output terminal and the adjustment terminal; that means a constant current flows through the current setting resistor and the load connected. Divide 1.25 by the current in Amperes (320 mA is 0.32 A and 630 mA is 0.63 A) to get the value of the current 'programming' resistor in Ohms. Go for a series or parallel combination of a couple of half-watt resistors so that you get as near the theoretical value as possible. For example, I used two 1 Ohm resistors in series that set the current at 625 mA.


Now onto construction. The three LEDs were wired as a series string with short bits of wire so as to fit the lenses in the holder. Pressing a piece of paper onto the lenses provides you with a template for this.

Cut a 2 mm thick piece of aluminimum sheet to serve as the heatsink backplane for the LEDs.

A disc with holes to clear the backs of the LEDs is cut from say an OHP film or plastic to serve as an insurance against short circuits.


Refer to the photos and make the assembly after spreading blobs of heatsink compound on the backs of the LEDs. The alu disc should now be a bit proud of the edge of the holder.

Now smear heatsink compound onto the disc and mount the heatsink with three screws onto the holder. Please note that the heatsink has to be drilled beforehand with the help of pressed-paper templates.

The LM317 also needs some cooling and has to be mounted onto the heatsink (using the third screw). Now wire up the current setting resistor/s and the connecting wires as per the following wiring diagram.

# Warning #
Please note that the metal heatsink slugs on the backs of the LEDs are fully isolated. But the heatsink tab of the LM317 is connected to its output pin. You don't need an insulator here so long as you ensure that all connections are well insulated and that nothing is connected to the metal holder or the heatsink.



Mount the SMPS pcb within a short piece of pvc pipe screwed to the top of the heatsink. The other end of the pvc pipe carries a mains lamp base salvaged from a fused CFL. Connect up the wires paying attention to insulation and safety.

Switch on and you should be rewarded with a really bright beam.
# # #  Be careful not to look directly at the LEDs  # # #  as that could cause some amount of damage to your eyes. It is better to put the lamp in a diffuser shade unless you want to use it as a spot light.
-----------------------------------------------
Warning:
If you want your lamp to be reliable in the long run, pay particular attention to heatsinking. A heatsink that might look and 'feel' adequate (remember the 'touch test' ?!) on the workbench might prove to overheat when the lamp is assembled into a holder-- if my experience is anything to go by! Use a substantial heatsink I did!) to keep the assembly really cool and drill adequate ventilation holes in the holder assembly. Usually the LED current would rise with rising temperature, but the constant current driver does offer some insurance here.
-----------------------------------------------

Another alternative that a friend tried out was to mount the LEDs onto a 1-foot length of aluminium channel used by fabricators of doors/windows etc. Drill small holes to fit the lens of the LEDs in a suitable strip of transparent plastic. Mount the LEDs smeared with heatsink compound onto the alu channel with a few screws that 'sandwiches' the LEDs between it and the plastic strip. The SMPS pcb, insulated well in a tube of plastic,  maybe slipped into the square tubular alu channel and the LM317 too may be mounted onto the channel. Mount two plastic end-caps (drilled for ventilation) on both ends of the channel and also screw on a piece of diffuser material in front, and you have a good, bright short "tube light" of sorts!

Naturally your imagination and ingenuity are the only limits when it comes to shapes and mounting options. Always be careful about safe wiring practices, the need for insulating connections etc, especially when working with high mains voltages. And don't forget to 'rate' your heatsink adequately with the "touch test" before using the lamp for any length of time.

Happy 'spot lighting' !!

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Thursday, March 22, 2012

PHILIPS REDUX - 3

'TOP-OF-THE-LINE' 40 WATTER

Again, here is another popular design with higher power output. Do note the protection circuits that have been incorporated; they worked very well indeed, as many would gladly attest. Quite a few of us had found that with an unregulated power supply and good components and a large, heavy heatsink, this design could take some beating! The circuit works very well without the protection circuit too, and for the experienced and careful constructor, the design has many merits even toay, I guess. If one doesn't want to 'brag' about the 'watts', this power amp could provide you with a solid foundation for your home-built system. Naturally quality of build and "setting up" the power amp are key factors in its sonic quality and reliability. For the younger brigade accustomed to "plug and play" with IC-based designs, setting up a quirky, high power amp would be something like a tight-rope walk, the art of which, once mastered, becomes easy and even enjoyable!








I am sure this foray into the past shall serve as the trigger for many new explorations, especially of a mature kind in search of true fidelity.

Happy DIY-ing !!

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PHILIPS REDUX - 2

15 W & 20 W  POWER  AMPLIFIERS

Back in those days, what separated the 'men' from the 'boys' was the output of their power amps; boys played about in the area below 10 Watts, and there was a 'grey' area between 10 and 20 Watts. The 'real' men occupied the upper echelons of 20 Watts and above. It was an expensive game when for umpteen reasons your power amp could 'teleport' itself into other worlds in a cloud of smoke, and to boot, take your precious speakers too along! And power transistors, especially matched pairs, were not exactly cheap and they surely did not grow on trees!

The 'flip side' of this power game was that in the melee, scant attention was often paid to the sonic merits of the designs. Considered from that angle, here are a couple of truly 'hi-Q' (a Philips trademark) power amps. If you have efficient speakers that do not need a connection to the nearest power house, these are wonderful options even today. I have found that the 15 W version is particularly suited to driving undemanding open-baffle speakers, and, be warned, the combination could sure sound addictive!

Perhaps what works the magic could in part be the circuit topology of these 'vintage' power amps.

Many of us could easily recall the mad race after fully complementary/fully symmetric designs. The designs looked particularly 'sexy' on paper with their picture-perfect symmetry and, of course, when well-designed, they did sound great too. But our obsession with such designs made us forget many of the golden nuggets from the past. Only recently have designers and enthusiasts like Wim de Haan and others done their bit to restore the quasi-complementary output stage as being 'sonically superior' to many other designs.

As a matter of fact the quasi-complementary design evolved out of manufacturing compulsions. It was easier in those days to fabricate high power N-P-N transistors. Fully complementary pairs were confined to the low power levels, and often used as drivers for the output devices. Now it is well documented by many designers in the field that there are subtle differences between the P-N-P / N-P-N transistors and as a result there are audible differences that mark the N-P-N pairs as being superior and "more musical" output devices. Whatever that might be, here is an opportunity for you to test that theory out with good quasi-complementary designs as these. Surely you will not be disappointed with the results!