The schematic hasn't changed from post #46.
It just needs power and ground to U1 (which is on the layout) along with the decoupling capacitors (the only moderately critical location is for the 0.1μF directly across pins 4 and 11 of U1).

The erratic behavior with LEDs can be related to their non-linear resistance with voltage.
A small (say 5-10W) incandescent in parallel with the LED may solve the problem with pulsing.
This bulb can be located anywhere, such as next to the circuit, whereas the LED can be on the tower.

 

Good Morning,

Okay, I printed out the schematic from post #46 and penciled in the .1uf decoupling cap that was added between pins 4 and 11 on U1 in post #51. I also penciled in the .1uf cap that was added between the junction of R6-U6 to GND in post #54.

However, a 10-47uf electrolytic cap was proposed by Dr Jones “next to the input J_IN” in post #53 (and approved by you in post #54) but I’m not sure how it’s to be connected.

Following my questions in post #80, I’ve since discovered that the “Clip Level” trim pot (U8) in your original schematic (post 34 and modified in post 37) is not shown in post #46. Has it been eliminated?

Thanks for tolerating my questions! I DO appreciate all of the help you’ve given me!

Harvey

 

The electrolytic can go anywhere from the V+ rail to ground.

DJ added the pot in post #58 but apparently didn't show the schematic for that.
See the pot labeled "CLIP" on the board.

 

Thanks! I think I'm good to go!
Harvey

 

Well, Sunday just wasn't my dayI

I got the "modulator" circuit loaded onto my breadboard but it didn't work. My 60w incandescent test bulb simply stayed at minimum brightness regardIess of what I did with the trimpots. I checked and rechecked the circuitry but couldn't find anything that I had miswired. So I pulled out my trusty Simpson 260 and started checking for proper V+ and Gnd distributions but didn't find any problems. Time to bring out the 'scope.

I worked with Tektronix 453As throughout my military career and got to know the model like the back of my hand. Therefore, when I retired and needed a 'scope to play with, I looked for a good used 453A on eBay. Found one but it died after a few months. So I got another one off eBay. It needed a lot of work to make it right so I looked for a third... I eventually ended up getting FOUR of them before I was able to build up one good one! (I probably spent less than $400 for all of them so I wasn't upset.) And then, on Sunday, I pulled out the working one to use (after about a year of it sitting idle), plugged it in and.........no sweep. Diddled with all of the horiz sync controls (and the 453A has LOTS of them, any of which if misadjusted can kill the trace) to no avail. Not in the mood to troubleshoot a defective scope AGAIN, I gave up and went into the house to drown my sorrows in a big glass of Cran-Apple!

Spent some time yesterday calling local oscilloscope repair services who all told me the same thing: The 453A was a fantastic scope - 40 years ago! Unfortunately, while they were once worth repairing (30 years ago), they're no longer so. They suggested that I look for a dumpster. Heartbroken, I crawled back into my glass of Cran-Apple.

Soooooooo...
Does anybody have any suggestions for a general purpose (i.e. "hobbyist") oscilloscope? Between model airplanes, model trains, and the occasional tower light modulator, I have only a sporadic need for one. It doesn't have to have a large bandwidth or a lot of features. Nor does it require spot-on accuracy. Oh, and I'd like one that won't go bad between uses (of which could be as long as 25 years) and costs less than $5. (Gotta save my money for a rapidly escalating Cran-Apple habit!)

Harvey

 

That's a bummer about your oscilloscopes.
What about a USB scope that connects to a computer such as this?
Connected to a laptop, they're reasonably portable.
They're cheaper since you aren't paying for a display.

Otherwise there are some digital scopes that are fairly cheap but I'm not familiar with them.
Here's a recommendation by one site.
I think the Rigol is fairly popular but don't know how well it's built.

 

This is probably more my speed...

http://www.banggood.com/DSO138-DIY-...saul&utm_campaign=SKU359936+SKU243635-US&ebay

Cute but probably useless.

Harvey

 

Well, you pays your money and you takes your pick.

As far as your circuit, double check all the wiring against the schematic. (I use a yellow high-lighter to mark on my checked connections on the schematic)
All it takes is one misplaced connection to kill the circuit operation.

 

Oops, maybe we've discovered the problem. I printed out a copy of the schematic and then used a RED, not yellow, highlighter to mark the connections as I made them on the breadboard.

I've already checked all of the connections and even double checked all of the polarities, etc. However, I'm not yet ruling out that I've miswired it. I'll probably strip it all down and build it again.

Stay tuned...

 

If you check all the node voltages and post them, it may give a clue as to the problem.

 

Status Report:
I checked my mocked-up circuit this afternoon but after awhile, all of the IC socket pins and breadboard jumpers started fuzzing together in my eyes so I elected to dissect it piece-by-piece. After it was completely disassembled, I couldn't find R3, the 250k, 1/4w resistor in the IC's feedback loop (between pins 2 & 8). It WAS in the box when I inventoried the Mouser order upon arrival. I also marked it off on the print when I breadboarded the circuit last weekend. And it wasn't on the workbench or floor tonight either. Hmmm!!! Nonetheless, I'm pretty sure that I lost it when I was disassembling the circuit, not when building it.

If R3 was indeed installed, the only thing left (and this struck me as I was both assembling and disassembling the breadboard) was that all of the components and jumpers seemed unreassuringly loose in the breadboard sockets. To remind you, I didn't get the most expensive breadboard on the market, but then again, I didn't think that I was getting the cheapest one either. However, maybe cutting corners on the breadboard wasn't a good idea. Any suggestions?

Harvey

 

Certainly all it would take is one bad contact to kill the circuit.
When you build the circuit again, use an ohmmeter to test all connections and trace out the circuit from the schematic.

If the breadboard really seems flaky, then perhaps you should consider buying a better one.

 

Can you recommend one?

 

Can you recommend one?

I'm not that familiar with them, but I would suggest buying a brand name such as one of these.

 

the components and jumpers seemed unreassuringly loose in the breadboard sockets.

One I bought some years ago had the opposite problem. You almost needed a hammer to get the component legs inserted .

 

Crutschow,
Digi-Key has quite a selection of brands and models! Is there a particular brand that you've had good experience with?

Mornin' Alec,
Welcome back to the thread. Can you recommend a breadboard?

Harvey

 

Sorry. It's so long since I bought my 'good' breadboard that I can't remember the brand or the supplier.

 

A quick search recommends 3M, but they are prohibitively expensive. I have one from Radio Shack 40 years ago.
But reviewing the Digikey offerings, I would replace mine with a Bud Industries... the $8.50 model. They are a well known firm albeit in the case and box vertical. Twin Industries also look like a potential candidate. At least I would consider them; I have been unsuccesful finding reviews.

However, now I very carefully design a PCB and have it manufactured.

 

Thanks Guys, I appreciate your inputs.

Welcome to the thread djsfantasi. In all honesty, probably EVERYTHING from Radio Shack was better 40 years ago!

Harvey

 

..............
In all honesty, probably EVERYTHING from Radio Shack was better 40 years ago!

EVERYTHING for the electronic hobbyist was better 40 years ago.
I'm concerned that in the future it will be difficult to find discrete parts that the hobbyist can even readily use (they'll all be tiny surface mount devices).