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Archive for February, 2012

29
Feb

Fuzzy’s Box

Way back in the 60’s I remember the first time I heard a FuzzTone. It was 1966 and a movie called The Wild Angles had a theme song called Blues Theme. It opened with a motorcycle starting up and driving off (a Harley obviously) and then the fuzzy guitar started in. I can still hear it, plain as day.

Since then I think a lot of players have covered the song, it was obvious that Fuzztone’s were here to stay. The Ventures had their own FuzzRite, there was the Gibson Maestro’s, Arbiter Fuzzface and on it went.

I haven’t actually owned on since the 60’s and I can’t even remember what I did own. I recall the smooth fuzz those so maybe it was Germanium transistor based instead of silicon. Lately I’ve been toying with painting so stomp boxes are what I plan on painting for.

Why not start with a Fuzztone. And not just any. I found a schematic for a FuzzRite and changed a few parts, added a bit of tone circuit and then came across a schematic called Green Bomb Fuzz that was so close to the one I laid out, I just used it instead of mine. So much for original thinking… It’s based on a Fuzzrite with some changes.

The box…the first thing is to get the box laid out, drilled, named, and labeled. Which is no small task. I using an airbrush and all this water based enamel is new to me (I spray lacquer for years). I decided to start with Createx paint. Good range of colours, supposedly ready to spray out of the 2oz bottles and easy to clean up. Well, one out of three isn’t too bad. It is easy to clean up…

I picked a dark blue metallic, which as it turns out is too dark… But what the heck. It’s just for fun any way.

With Flash

Drilled and painted. Next up, design the graphics…which I admit I just used web images.

Rat Fuzz LED

This is the real box but the knows and controls are just for show, a mock up. I used Rayven Repro Film to laser print a full label. Rayven is fabulous but expensive stuff. Self adhesive so it’s easy to apply and once it sets up it sticks quite well. I was going to clear coat the box any way.

I applied the clear coat and this is what it looked like all painted up. Yep, dark blue is too dark…

Top Clear

In my opinion Createx needs to be thinned slightly, and it doesn’t “flow” worth beans. Trying to get a nice gloss finish was very very hard compared to other paints I’ve used. So I guess for $4 you get $4 worth of paint.

One of the BIG issues with Createx is you need to heat cure it. Or it never really sets up and dries. I used a heat gun to get the temp of the stomp box up to 150F. At that point the paint “fades” or “dulls” down. You really have to put a clear coat on to bring back the gloss. Again, not what I’m used to. The Gloss Createx isn’t really all that glossy either. So far, not impressed with Createx “entry level” stuff at all.

It takes a lot of “thin” coats to get a nice finish. I wouldn’t use the heat cure stuff again. Don’t like it. I might try the AutoAir. I have sprayed some Testors and that actually went on quite nicely.

I laced on the clear coat pretty thick and it doesn’t feel like I should have to do that. But hey, enamels are something new to learn…

Next installment…building the circuitry..

27
Feb

Flying a 737…

Andrew got me thirty minutes in a 737 flight simulator from Flight Adventures for Christmas and I finally got to use it!

The sim is out at YVR (Vancouver airport for the lay people) and in one of the oddest places you try to drive to. Felt like I was going down an alley and the the guy who runs the place, Jason, played telephone tag with me. I was on time, he was running over from the last client. Seems a lot of his clients are real life pilots. I’m not. Since he’s the only guy there and in the sim, the doors are locked and the lights are off until he’s out of the sim.

The nondescript door of the place makes you wonder if you’re in the right place…the only clue is the 737 in the window.

IMG_2710

Once you’re inside, you get a QUICK briefing on the 737. A lightening speed look at the controls with a mention of what controls you’ll be handling.

IMG_2714

Then it’s off to the room that has the sim in it. I’d seen flight simulators before, ones that are mounted on hydraulic systems with video so you get the full feel. Those normally aren’t for the general public, unless it’s Disneyland…

Captain WestJet…:-) And when you’re in it, that’s exactly what it looks like…

console.jpg

Lower part of the console and dash (the horizon thingie on the left is your “guide”)…computer on the low console are for programming your route.

Full view 2.jpg

Sitting at YVR 08 waiting for take off clearance…ah screwem’ I’m going for it..:-)

YVR 08.jpg

It sure ain’t first class…:-)

Full view.jpg

Thus I managed to take off, fly out over Pitt Lake, do a 360 back around, had to Victoria and land. The only iffy part was the bunny hop landing. Jason ran the throttles and flaps, I did pretty much every thing else. I suspect he keeps it simple for everyones enjoyment…

There’s two things I picked up from this half hour. First is, Jason cobbled all this stuff together into a rather accurate 737 simulator. Looking out the window when you do a turn, you swear you can feel yourself moving. The sim doesn’t move, you do! Really weird. Same with climbing and descending. It feels very real and the when you pull on the speed brakes it makes the same noise I’ve heard a lot of times before. I was waiting for the “bump” of the gear coming down, don’t remember if it did that or not.

Hence Jason is a first class nerd (he’s never flown a real 737) as well. His passion is this sim and he expects you to treat it with kid gloves because that’s what he does. And really, you don’t want to toss a 737 around the sky any way. Use a Pitts Special for that.

Second, pilots apparently use the auto pilot rather heavily. Like from almost take off to landing (on landing autopilots can auto brake but don’t steer). So the pilot is a great programmer as well, but you have no idea if they can fly or not…least you hope you don’t have to find out. Even so, flying the thing manually or programming the legs of the journey keeps you busy. I flew for half an hour and at the end of it I was exhausted. Obviously a veteran pilot would do this like a walk in the park, but I have a whole different appreciation for their skills.

If there’s a downside to Flight Adventures it’s the business end. They have a fabulous product with a great looking web site. And quite clearly not a clue as to how to market or promote their product. if they have competition it’s probably a Nintendo or a PS3. Which quite honestly don’t hold a candle to the simulator Jason built. The only super accurate slight simulator I know of is X-Plane and they have a Pro version.

In short, I hope Flight Adventures works out a decent business model because flying the thing is a hoot. Although I do wish they had a helicopter one…

26
Feb

Spray Booth update

I was spraying up a stomp box today, shot the main colour and that was okay. Later on I tried spraying the clear coat. Man was that hard. Even with all the LED’s I added, there were shadows in the front…

Before front light

As anyone can see the front edge, like the one I’d be spraying, is in the dark. If you’ve done spray painting at all you know you need light to see the “wet” paint… So I added a set of LED’s that are removable in the front…

After front light

I put some velcro on the wood so I wouldn’t bump it, wired in a short jumper and connectors and it makes a HUGE difference. Now, if I’d done that BEFORE I got the run in the clear coat…

18
Feb

Genz Benz 60LT Acoustic Amp

Having an acoustic guitar and several guitar amplifiers means that I could plug in and use the built in pickup in my Fender Sonoran SE.

What I’d noticed in testing out electric/acoustics was that they used different amps than what your standard Tele or Strat might use. Initially, I was thinking “marketing ploy” but when I started to try some, yeah, they sounded a lot different. The idea of an acoustic amp is to make it louder without colouring your sound. So as usual, talk to a bazillion people, read reviews, and try out as many as I could to see what i liked the sound of.

Most of these amps are quite small, i.e. no Marshall stack (Marshall does make an acoustic amp though)…speakers range from a couple of 4″ to a single 12″ and anything in between. Almost all are stereo, which is interesting considering the guitar is a mono source. Wattages range from 15 to over 300. Yea, 300 watts through a pair of 10″ speakers (with tweeters).

Fishman acoustic amps are first and foremost, every friggin’ where. If there were any more, you’d have to start a spraying program to stop them breeding…I tried several different variations of their Loudbox Artist and Professional. Attractively priced. Sound did bupkiss for me.

From that point, I worked my way down the line…and happened to be out at SurfSide Music. Noticed they carried Genz Benz in a solid state series called “Shenandoah”. They went from 45 watts to 300 watts with various speaker compliments, effects and input/outputs. The king of the hill is the Shen ProLT or the 300LT. Loud doesn’t adequately describe these things. Deafening would be closer. None the less, I didn’t care for the sound of either, nor the price…

Then I tried the Shen LT60. Bingo. First amp that I tried that didn’t change the sound of the acoustic guitar. Just brought out it’s natural sound. I wondered what could be making all this wonderful sound and…a pair of 6 1/2″ speakers and matching tweeters. 30 Watts driver each pair for a 60 watt amp. Who’da thunk.

Genz Benz 60 LT.JPG

Specs:

• Lightweight 29 lb design
• Stereo 60-Watt Power (30 Watts per side)
• Stereo 24 Bit DSP w/ 16 Preset Digital Effects
• Two Channels w/3-Band Active EQ w/Sweepable Mids
• XLR and 1⁄4” Inputs
• Headphone Jack
• All Input Signals Mix Together
• Dual 61⁄2” Woofers and Bullet Tweeters
• Compact Monitor-shaped Cabinet Design
• XLR Direct Outputs (Left and Right) w/Ground Lift
• Phantom Power for Condenser Mics
• Speaker Stand Mountable
• Protective Metal Speaker Grille

Coming from a world of BIG 4 x 10 or 4 x 12 cabinets, it’s hard to explain how much volume/tone this little amp can pump out…with the mic input I can even caterwaul along with myself…

I recently checked Genz Benz for the LT60 and it would appear they don’t make it any more. They have an LT80 now.

If there’s one annoying “feature”, it’s that the designer(s) overlooked the fact that the amp thumps when you power it up and when you power it down. It’s a solid state amp, it has a DSP. When the DSP comes online, it thumps the speakers. Turn down the “effects” gain before power up and it doesn’t do it. I emailed the company and they suggested doing just that, turn down the gain, power on the amp, turn the effects gain back up.

Which is like saying: get in your car, turn the radio volume down to zero, start the car, turn the radio volume back to where it had been. Every time.

So Genz Benz, lovely little amp, good sound, sturdy but for the glaring oversight on an amp in this price range – FAIL.

Thus, I do like the sound, I tolerate the thumps because some engineer was probably polishing his resume…I hope.

17
Feb

DCA55 – Analyser

Every now and then there’s a big of test gear that comes along that is simply, for lack of a better expression, drool worthy…

As I designing and building some stomp box pedals, I was trying to match up transistors according to gain (hFE) or B-E voltages or whatever. Plus I was looking for lower gain transistors in some cases or higher in others. Just looking at a heap of them in the parts bin doesn’t really tell you much.

Of course the manufacturers specs are always around, and low and behold, some of the parts even are within spec. Some aren’t. Then there’s others that don’t have any numbers or house numbers on them and you wonder what the heck they are. Sure with a multimeter you can figure it out…but I happened across a Peak Atlas DCA55 Semiconductor Component Analyser. Now with a name like that, it HAS to be good…

I checked the reviews and educated myself to it’s pros and cons. The only con I could find was if you were testing 40 year old Germanium transistors with hFE around 10-15 the tester was going to have a fit. Usually saying that it’s either a faulty device or unknown. Since that’s unlikely to occur for me, I ordered one from the UK company that makes them. Because there’s nowhere else that seems to have them. Cost is about $100.

Comes in a nice little box, 12V battery, about the same size as a point and shoot digital camera. Yep. Small. Three leads to connect to “whatever”, two switches to test with and that’s it.

What will it test? Diodes, diode networks, LED’s, Bicolor LEDS, Bipolar transistors (BJT), Enhancement mode MosFET’s, depletion mode MOSFETS, JFETS, SCR’s and TRIACS. Covers the majority of the stuff in my parts bins…

So the first thing I did was plug a common cathode tricolour LED on the leads. Any leads by the way, it will tell which ones are which. Yes, I know mine is a tricolour but this was a test.

BiColor LED Test.JPG

Don’t know what leads do what? Click the scroll button on the DCA55…The RED lead is the cathode. Now if you’re thinking it MISSED the green lead, it didn’t it tells you the details about EACH led it found, so I was only checking the one in the photo.

Next up, grab a transistor and plug the leads on (TIP122)

TIP122.JPG

But what leads are what? EASY!

Tip 122 Lead ID.jpg

What about GAIN (2N2904; spec says 40-120 for hFE):

Transistor hFE.JPG

The DCA55 comes with a well written 25 page PRINTED manual and the thing is a piece of cake to use. A one year warranty, and a COMPLETE listing of all the test parameters the DCA is using to give you the results.

So like I said, this is one drool worthy piece of kit. Money well spent as far as I am concerned…

16
Feb

Offshore Mail Delivery

I tend to order a lot of little bits and pieces from mainland China and it feels like the post office lottery when you try to guess the delivery date. Some are here in a heartbeat (or two), where as others take 6 or 7 weeks. I’ve searched online to try to find the answer and today I think I found it.

When the shipper doesn’t pay enough at the post office, they get this method of shipping:

slow_boat_from_china.jpg

14
Feb

El Sleezo LCR Meter

It goes without saying that if you need an LCR meter you should buy a good one. If you’re an engineer or electronics designer you probably have a top notch unit with a calibration sheet, and, you’re hardly the type that is going to get anything useful out of this post at all…except maybe a chuckle…

For the unwashed electronics masses, of which I am one, we simply need something that can get the job done.

Enter the El Sleezo line of meters, tools, parts, or whatever. They all come from the same place (offshore; but you knew that). The quality test on El Sleezo stuff is generally performed at the speed of light. I concluded that because no one in their right mind is going to reach onto the assembly line that travels at Mach 5 and risk life and limb to grab one of these “whatevers” for testing. Nope, testing was done during the design phase. Returns and DOA’s bad Karma.

My eyes, along with other parts of my anatomy, which we won’t cover, aren’t what they used to be. Reading little capacitors to determine what value they once were or might have been, assuming there are some numbers still to be seen, is just too difficult. So I needed a capacitor meter. There. I said it. Notice I didn’t say I needed a good one.

I didn’t need an L or R meter (inductance or resistance). I can read resistors without problems. I rarely work with inductors except for those few times when I forget the mains are live and volunteer to “induct”. At which point I do resemble an inductor. I choke, coil and react. Sometimes all al the same time. Truly amazing.

eBay has a LOT of LCR meters. Some of the local electronics shops carry the same “value” meters at a premium price. And of course theres some good stuff around. Unfortunately you’d have to miss a mortgage payment to afford it..but still..

For brands, there’s Vichy, CA-4070L, MasTech, Extech, and so on. Lots to pick from. For $30-$50 you get one of the low cost units and The Vichy DM4070 I got cost $30 (free shipping!)..

I honestly didn’t expect much, just something that if I blew it up or broke it, it wouldn’t break the bank.

Vichy DM4070.jpg

It arrived in a multimeter box, which confused me until I realized that they are recycling boxes “over there”. So that’s not a bad thing. I got the required cute little manual that compretely x-sprains opa-ration of un it. Yea, you want a chuckle, try reading the translations. For example, the one that I found in the “diaper policy” section:

“The Function stated for this User Manual cannot be reason of special usage.”

Or better yet:

“The content of this manual is regarded as correct, error or omits. Please contact with factory.”

That one should set off some alarm bells some place…

You get couple of leads, no 9V battery, the manual and meter. Have to say that the digits in the meter are HUGE. I could almost use them for our house address out front. There’s a zero adjust pot for the leads stray capacitance. On the lower scales it’s a little touchy but it works. The meter has blade sockets so you can just shove in a cap. Okay, these were may out of some old soda pop can but they work. For now.

I tried turning it on. Found that I had to hold down the button because it wouldn’t latch. Who wants to have a half functioning piece of doodoo any way. So I took it apart (credit EEVBlog for that tag line).

Vichy PCB.jpg

Notice that mine is water marked, or something. Maybe a repair for a bad connection. Hummmm. Around the power switch too. Turns out there was nothing wrong with the PCB at all.

If you look at the photo below, you see the power switch on the left under the display. That’s nothing but a chunk of plastic attached to a pushbutton switch. And after looking at it, I see the plastic had a piece of flashing on one side that hindered its movement. Couple of seconds with a nail file and plastic is nice and smoothy…

Vichy Inside.jpg

I put it back together, stuck a battery on it and tried the switch a LOT. Works perfect every time. Checked a bunch of caps with it and yep, it works. Not sure I’d want to shove a charged up electrolytic capacitor into it since it doesn’t look to me like there’s much in the way of input protection on this meter. Well, other than the PCB foil traces…

And as you can see the blade sockets for the caps are well, ah, stellar isn’t the word I’d use to describe them. The rotary switch is one of those wiper jobs that after a lot of use will sand through the PCB traces and render the meter fit only as landfill.

For intermittent use it’ll probably last a while. Or not. Maybe they need to add a tag line like this to the manual:

Life expectancy of unit is subject to change without notice.

13
Feb

El Sleezo MIDI Interface

If you’ve ever been surfing for a MIDI interface, I’m positive you’ve seen the likes of these ones:

MIDI Interface.JPG
They are littered all over the internet from a variety of sources from Amazon to eBay. Commonly called “USB To MIDI Keyboard Interface Converter Cable”, or some variation thereof.

Usually selling for the awesome sum of $5. If you’re wondering how they can build one of these for $5 and make a profit (when they even off free shipping), I have no idea either.

These things have peaked my curiosity for some time and since I’m not a feline, I took the bait…er plunge and ordered two of them. One from Amazon, one from eBay. After receiving both, it was obvious that they are from the same factory. There are no drivers to install, you just plug them in and..well…pray. Which is exactly what I did…

On my Mac system, they show up as “USB MIDI Cable” in my MIDI interfaces listing. Probably the most generic name in the world, but what the heck. No drivers.

Any way, I fired up my testing software and ran these through their paces. I expected the worst. I mean, what do you get for $5? A Starbucks latte? Maybe. Thus I was pleasantly surprised when the darn things actually work. Send MIDI, receive MIDI. Send SYSEX, receive SYSEX… they actually work.

Now lets stress them a little…ah ha. Hit them with a high traffic stream and…bingo. We got some issues. Our old evil friend Mr. Latency. Now the latency is not so bad that you could measure it on a calendar, but it’s there. Near as I can tell 9-15ms. Kind of varies. Probably not the largest buffer in them nor well written software (I’m guessing a PIC chip in them).

For standard low stream MIDI, you’ll probably get away with it and think they work perfect. But for multiple SYSEX messages (like doing a dump from a MIDI CPU where it sends umpteen SYSEX messages one after the other), or some really high traffic MIDI data, ah..nope. Fail.

Of course it “tries”, kind of like the little engine that could, but didn’t. You need the briefest of pauses between multiple SYSEX messages and it’s as happy as a clam though.

The reason for my testing these things out was that I wanted to see if it really needs a driver (no it doesn’t), does it actually work with SYSEX (yes it does, as noted), and is it really worth the $5 (yes it is). I wasn’t looking to replace my 8×8 MIDI interface that does routing, or even my M-Audio UNO. Just something I could toss in a gig bag or drawer, pull it out, do some SYSEX programming and toss it back in the drawer/bag.

The only thing I haven’t done is plug both of them at the same time to see what happens. And I’m not going to. No use tempting fate…

11
Feb

Spray Painting

Finally got all the bits and pieces for the airbrush and compressor so it was time to paint up a box (the LED Tester I was making). Since I was going to have black lettering on the box, the best colour for the box was going to be white. Of course, for me, white has to be one of the hardest colours to paint just because it’s tough to see the build up.

That was hardly going to stop me though…so here’s some sample shots of me “in action”…That’s a Badger 200NH with a 1/4oz side cup. I think a standard box will take about an ounce so I could have used one of the 2oz bottles. So I had to refill the side cup quite often (use pipettes to do it!)…

AirBrushing.JPG

A little close up of it…

Airbrush_Closeup.JPG

And completed:

Airbrush Bottom Done.JPG

No mist came out of the box, the filters grabbed it nicely. The turntable made it easy to spin the job and paint it all the way around. The LED’s on the top helped me to see the wetness of the paint because, as I said, white for me is a tough colour to paint…

All in all, the spray booth is a complete success.

There are some additional things needed. One is a proper cleaning bottle:

Airbrush Cleaning Bottle.jpg

With this you put some water into the airbrush, then spray it into this large glass container. No mist comes out (it’s filtered) and the water based paint stays in the bottle for easy clean up. Ihave one on order so it will help in the future.

10
Feb

LED Tester Completed

So after shooting some paint with the new airbrush, sticking on my labels, adding the circuits to the inside, the LED Tester lives…actually works quite well.

LED Tester Inside.jpg

Lotsa room in there…standard stomp box enclosure…

Just plug in the LED to the top connect, select the current range, hit the TEST button. I like simple.

LED Tester Top View.JPG
4
Feb

LED Tester Software

While looking for circuit drawing software, I happened across an app that I’d gotten for the iPad a while back (and promptly forgot about having)…

It’s called iCircuit and talk about slick. While it still doesn’t have ALL the bits and pieces for doing schematics, it’s got a good deal more than Fritzing plus it does allow you to “run” the design. You can scope various points so it’s very much like the old Circuit Maker.

LED Run.PNG

It’s in RUN mode on the iPad 2, you can see the switches that are closed, the current draw at that point. To open or close a switch you just click on it.

The plain schematic looks like this and you get a parts listing out of it too. I was pretty impressed with it.

Constant current.png

2
Feb

Led Test Schematic

Finally found a piece of software that allows me to at least do some basic drawing of a schematic. The software is called Fritzing.

This is not a review of the software, just my personal impression of it.

I think it’s designed for taking a circuit that you’d build on a strip style board, which creates a schematic (of sorts) from what you lay down. From there you can create a PCB and save it as a Gerber plot. A high percentage of the examples of it in use show it coupled with the Arduino devices. I suspect that’s a lot of it’s background and judging from the lack of “core” components you can work with on a schematic, it seems to bare that out.

When I design circuitry, I don’t normally work on anything overly complex, I start with a schematic. From that point, I can almost always turn that into a PCB by hand without too much work. When you do it this way with Fritzing, you get some interesting results because that’s not the way it was designed. But then I’m old school too. I was designing PCB’s before there was software to design PCB’s and “auto routing”….

So here’s what I managed to “draw” in Fritzing. First off, you’ll see that I have switches S3 thru S8. Actually in my circuit that’s a rotary switch. But there’s no rotary switch in Fritzing. Matter of fact in Fritzing the “input” section is pretty skimpy. DPDT? Nope. Pushbutton? Nope. And on it goes. While you have the option of defining your own parts, one look at the multiple steps required to do this and it pretty much cures you of that idea.

Which is not to say that Fritzing isn’t useful, it’s remarkably good at what it does. However, if you’re schematic based like me, you’ll find it lacking in a lot of areas. So keep in mind that it’s free.

LED Constant Current Tester.jpg

Ages ago (we’re taking in the early 90’s) I used a piece of software called “Circuit Maker” from Microcode Engineering for my Macintosh systems. Not only could you draw a work schematic but you could “run” your schematic and put scope points on it to watch logic signals change. Of course resistors or capacitors didn’t affect the circuitry for “simulation” it was just logic gates. But you could set propagation for those gates. I built a lot of digital circuits in those days with that little program. I still miss it.

Eventually, Microcode dropped the Apple Mac support and continued to develop for Windows. I think they’re up to version 5 now.

After that I ended up using Canvas from Deneba Software and I had an electronics symbol library that I could draw schematics with. It wasn’t bad either. Course if you started to move parts around the wires came apart pretty quick because there weren’t any real points. Then Deneba got tired of Canvas and flogged it off to ACDC who didn’t give a squirt about the Mac clients. The software was let lapse and one of my most used drawing programs went the way of the DODO bird. If Lion would run Rosetta I’d still be using Canvas 8. But in another Apple’s infinite bouts of “we know what you want more than you do”, Rosetta is gone.

Finally I used OmniGraffle and its electronic symbols to draw schematics. And it worked, but I never seemed to get really comfortable with it to continue using it.

Softwares nature is to be a good revenue generating machine and if it’s not, it’s dead pretty fast. There’s scant few hobbyists like myself that program for fun and little to no profit. Unlike many, money has rarely ever been a motivator for what I do. Regardless of what it is. I write software that I need. Turns out other people seem to need it too, but writing for profit is something I only did once, a long time ago and I never did it again.

Any way, I’d love to see something like Circuit Maker for the Mac again….hey, I can dream can’t I?

So then, probably like a million others, my schematics are drawn on the back of a coffee stained napkin in an all night donut shop…

1
Feb

LED Tester

Having bought about a quadrillion LED’s off eBay and from other sources, I notice that when they aren’t on, they sort of all look the same. Occasionally I grab one, manage to get the right colour and put it in a project. Only to find out later that I should have picked one that wasn’t as bright or one that is brighter. Sort of a duck shoot really.

I’ve looked at those LED testers from eBay and thought, what the heck I could make one myself. Not that it would save any money since the ones on eBay or in kit form are dirt cheap to start with, but still, there’s the creative side of it that intrigues me…

Initially I thought for testing LED’s I’d just use a bunch of resistors on a rotary switch and use that to change the current to the LED. Which is find in theory but when you factor in that different colour LED’s use different voltages it didn’t take long before I could see the error in my thinking (seconds really)… Blue or IR can use 3.6V 20ma, where as red might use 1.9V 10ma. That’s a spread.

Thus a constant current source is what was needed. I could vary the current source to try the LED at whatever milliamp I wanted (to a point or smoke if you like)…I estimated a values from 5 to 50ma should cover the LED’s that I deal with all the time.

The simplest ideas, require the simplest parts. Couple diodes, few resistors, one transistor, some switches, a box, wire, battery and that about sums it up.

My circuit board:

LED Tester Board.JPG

Diodes on the left with the resistor, one good ole fashioned 2N3904 NPN, and a bunch of resistors to do the current limiting (12-120 ohms). Nothing fancy, but it works nicely.

Here’s a shot of the box, label and all the circuitry. That’s a 4 pole 4 position switch, but I’m only using 2 poles. I switch between them so one pole is three low current settings 5, 10, 15 and then 20, 30, 50. I wired them a little different than that so I can toggle 5-15, 10-20, 30-50 with the SPDT toggle switch.

For the LED to test, I’m just using an RC battery connector, and it’s not wired in the circuit yet. Have to paint and get the box ready first.

LED Testor Connections.JPG

I’d have put the schematic here, but trying to find some simple to use software that allows me to drop symbols on a layout is apparently more difficult that I envisioned. I used to use Mac Circuit or something about 20 years ago, but that’s long gone now. So I’m still looking for something simple that doesn’t require a second mortgage to buy.

I’ll try to post the schematic….