Signal Tracer - Requesting input on requirements

[sam_sam_sam]

Re: Signal Tracer - Requesting input on requirements

I have one comment about the capacitor across the other pads ( in the second picture) is you might want to put heat shrink tubing on the component leads so nothing bad happens ( just a thought )

Nice work

[clearchris]

Re: Signal Tracer - Requesting input on requirements

Your board schematic was missing two capacitors that I always include, on my schematic in Post #10.
If the LM386 is doing RF oscillations (around 13MHz shows up at higher output power) it will sound trashy. Make sure it's got a bypass cap like 2.2uF X7R across pins 6 and 4 right at the IC. The 220-1,000pF cap to block RF/AM radio at pin 3 In(+) to GND is important too. Sometimes I mount it at the pot.

The potentiometer housing is best to have a ground connection tack-soldered to the housing, like they do in electric guitars. Just a small jumper from the case to the pot's ground terminal, without melting everything. Sometimes I scuff and scratch the pot's can to make solder stick.

Keep the loudspeaker wires away from the input wiring, best is a shielded cable from pot to board. The speaker wires do radiate several volts at higher volumes and the wires right next to each other

Important on the star-ground is the power/battery (-) and speaker (-), LM386 GND pin 4, all go to one point as best as possible.
I can't see a pic of your board, sometimes they are done poorly for pcb layout.

It's worth it to tame this thing and get it to work without killing sensitivity.

I made all the changes you proposed earlier. The only differences I can tell between your schematic and my board is the LED resistor is 4.7k instead of 10k, the cap before the speaker output is 1000uf instead of 300uf and I'm running a 12v buck converter off a 20v SMPS for power. I also substituted a C0G cap for the 2.2uf ceramic cap.

The 2.2uf cap is mounted to pin 6 and pin 4.

I attached the pot case jumper to the ground pin on the pot. That resolved the issue that touching the pot causing the sound to change.

I do have a 1nf cap on pin 3, but it's on the PCB, much closer to the LM386, I can move it to the pot if you think that would help.

I can add shielded cables. I have some balanced 2 16ga conductor with copper shield cabels, but they are really thick, closing the case could be an issue. RCA cables are usually shielded right? I don't have any other shielded cable on hand, so maybe I could sacrifice an unused RCA cable and get this going...

I have tried many times, but once I add the speaker connection to the star ground, I get only super-faint sound from the speakers. It's so quiet I can barely hear it. Any ideas?

Pics attached of the board, front and back. The two diodes and resistor are hidden in some heat shrink, but are present.

[redwire]

Re: Signal Tracer - Requesting input on requirements

Your board schematic was missing two capacitors that I always include, on my schematic in Post #10.
If the LM386 is doing RF oscillations (around 13MHz shows up at higher output power) it will sound trashy. Make sure it's got a bypass cap like 2.2uF X7R across pins 6 and 4 right at the IC. The 220-1,000pF cap to block RF/AM radio at pin 3 In(+) to GND is important too. Sometimes I mount it at the pot.

The potentiometer housing is best to have a ground connection tack-soldered to the housing, like they do in electric guitars. Just a small jumper from the case to the pot's ground terminal, without melting everything. Sometimes I scuff and scratch the pot's can to make solder stick.

Keep the loudspeaker wires away from the input wiring, best is a shielded cable from pot to board. The speaker wires do radiate several volts at higher volumes and the wires right next to each other

Important on the star-ground is the power/battery (-) and speaker (-), LM386 GND pin 4, all go to one point as best as possible.
I can't see a pic of your board, sometimes they are done poorly for pcb layout.

It's worth it to tame this thing and get it to work without killing sensitivity.

[clearchris]

Re: Signal Tracer - Requesting input on requirements

Ok, somehow I figured out the buzzing. I had a 1/8" audio jack from my mobile phone to a 2 rca jack cord, with one rca jack plugged into the signal tracer assembly, the other hanging free. If I touch the ground on the second RCA jack, the buzzing goes away. Pretty strange that the buzzing only cuts in at a very defined location in the pot and cuts out as I turn the pot up. I'm sure there's a very technical reason for this... Highly sensitive signal tracer as promised!

Anyway, the static is still there, it doesn't seem to be affected by moving wires, touching things, etc. It's the same volume when the pot is turned down and turned up if the mobile phone is muted. I'm starting to think that I might have a substandard LM386 chip, but I'm not convinced.

I did some more experimenting with the star ground, and I have found that I can connect the LM386 pin to the star ground, but I can't connect the speaker to the star ground, speaker ground must be connected back to the PCB at the designated "speaker" JST connector. I'm going to do some more experimenting...

[clearchris]

Re: Signal Tracer - Requesting input on requirements

Well, I soldered a wire to the back of the PCB on the LM386 to pin 4. When I added that to the star ground point (power, pcb ground, speaker ground and pin 4), I wasn't able to get any of the signal (some noise) out of the speaker.

I also noticed that there was considerable noise from the wires that went to the 1M pot. Moving those wires around caused considerable noise and even touching the knob on the pot caused considerably more noise. I could add the 1m pot ground to the star grounding point, would that help anything? Right now all three wires are run back to the PCB. Could I add a magnetic core to help suppress the noise?

Also, how much noise should there be when I turn the volume pot all the way down? Right now there's a pretty decent amount of static.

Any suggestions would be very appreciated. Thanks!

[sam_sam_sam]

Re: Signal Tracer - Requesting input on requirements

Everything is together

BTW, the red dot that looks like it might be a reflection isn't a reflection, it's the LED behind maybe 1mm of plastic. I have grown to like this effect, having done it once before by accident.

Very nice work

I need to put my 3D printer back together so I can do some printing projects I had redone my office where I had my 3D printer but I got a spool heater for the filament and I made a holder for the spool heater ( with the spool heater it would not fit in that spot anymore)

So I have to hook up everything on one power supply so let see how this works out

[clearchris]

Re: Signal Tracer - Requesting input on requirements

Everything is together, pictures aren't the greatest, but decently happy about how it came out. It would have looked nicer in PLA, but I have been trying to use PETG. The wires are a bit of a mess, but that's partly due to there just being a lot of wires...

There's a bit of buzzing that changes when I move the wires around, but I have to do the star grounding yet. I hope that fixes it. I just reread redwire's instructions and realized I need to attach a wire to the amp IC pin, so that's going to wait until tomorrow when I can take it apart, solder a flying wire in under the board, and reassemble it.

Overall, either the case mounting or the amp mods (thank you redwire) have definitely increased the level of sound coming out of the speaker. It's decently loud and clear for its size. Of course, it's not perfect fidelity at higher volume, but I can't expect much out of this speaker size. I'm definitely glad I included an RCA jack on the back, this would make a decent speaker on my bench for some tunes in a pinch.

BTW, the red dot that looks like it might be a reflection isn't a reflection, it's the LED behind maybe 1mm of plastic. I have grown to like this effect, having done it once before by accident.

[clearchris]

Re: Signal Tracer - Requesting input on requirements

It took me a while, something was bothering me about the back case, but I couldn't put my finger on it. I ended up changing a few small things, it's printing now. I should have something to show soon.

[clearchris]

Re: Signal Tracer - Requesting input on requirements

That's interesting, I'll try the sock trick.

Why would you want step files for smd parts? Doesn't the pcb layout software you use have all that?

[redwire]

Re: Signal Tracer - Requesting input on requirements

Adding some acoustic padding behind the speaker does help a lot to improve sound. I've used rags or an old sock folded up behind the speaker to lessen reflections on the backside.

I'm using GrabCAD library for electronic parts i.e. 3D models by Alex Federov he's using Russian CAD software that makes very compact models. Solidworks makes fat bloated .step files just huge, look inside one and laugh.

[clearchris]

Re: Signal Tracer - Requesting input on requirements

My mouser order should arrive by Friday, so I should be wrapping up this project soon. Which means... new project time!

Kind of related to this thread, I'm going to bulid this, a 3d mouse for freecad.
https://github.com/mnesarco/HyperController
If anyone is interested, I'll post some links to the parts and go through the build.

[eccerr0r]

Re: Signal Tracer - Requesting input on requirements

.. as long as the models are available, that's the rub.

End up having to fake it, some of these would take too long to model themselves *sigh*

[clearchris]

Re: Signal Tracer - Requesting input on requirements

You still have to do a fit test, you can't trust the models completely, but the models are remarkably good for visualizing the solution together. I don't bother with screws, I have rules of thumb I work with. Holes exactly the size of the screw are good for threading, add 0.2m for a light fit.

[eccerr0r]

Re: Signal Tracer - Requesting input on requirements

Well, parts like speakers, BNC connectors, ICs, ... I guess screws and stuff is available, otherwise I've been having to make my own everything to get a fit test...

[clearchris]

Re: Signal Tracer - Requesting input on requirements

Make sure you have enough hard edge free surfaces inside your case so you'll less likely get resonances, heh. Then also trying to increase the effective air volume in the path so you can get better bass response too...

I made no attempt to better the acoustics, I have read about speaker enclosures before, and it seemed much like antenna science, there's so much to know before you can hope to be effective.

I can round the interior corners, do you think that would help? I can also pretty easily add ports, etc, but again, I haven't the slightest idea how to size any of that type of thing.

Currently using OpenSCAD at the moment with Cura as my slicer. Talk about obscure CAD programs, that even less likely has libraries available.

No libraries for openscad? Look on thingiverse. There's plenty. I use freecad or openscad, depending on the situation. They seem to be the most supported open source CAD options. If you really want to feel pain, check out Blender. Some people use it, but I imagine those are the ones that use if for it's other strengths.

FreeCAD looks intimidating. I don't quite get how to move and make pieces around yet. And then attaching pieces together...

There's three workbenches in freecad. "Part" and "Part Design". To get going quickly, you can cobble some things with primatives in "Part" quickly. If you have wierd shapes not handled by primatives, use "Sketcher" and extrude the shapes. If you want to make parametric designs, use "Spreadsheet" and name some cells. You can then refer to them in the other workbenches. Once you get the hang of Sketcher you can graduate to "Part Design". I personally find that "Part" is easier to build your own library of commonly used shapes for reuse. "Part Design" you are making sketches in place to affect on object, it's hard to explain until you do it, but I find it's harder to reuse pieces. Though I don't have as much experience with "Part Design" so I could be wrong. Use "Mesh Design" to create a mesh from your design and export to STL.

To specifically answer your question, in "Part" there are a series of icons for boolean operations that consist of two overlapping circles with different shading. You will know what they mean when you see them.

I find that freecad is much easier to use than openscad when you have a design that's modelled around an object you can find on grabcad.com. You import the piece you are using, the build your object to fit. If you look at the pictures in this thread, nearly everything except the enclosure and grille was pulled from grabcad. It's much easier when you can see how everything fits together before you print.

Before, I used a mono 3.5mm jack and some leads with alligator clips. This works but noisy with high impedance circuits and probing with an alligator clip can short stuff out on a board.

I have a pair of nice multimeter probes that I was planning to use, thus the banana jacks. One gets an alligator clip attachment for ground and I can go hunting with the probe and a covered tip.

Adding the BNC - I found a scope probe great for poking around equipment. It's shielded cable so no hum and noise picked up, and the tip or clip handy, no accidental slips. The X10 I can use if high voltage up around 300V or more if you have guts.

That's a good point about shielded cable, I hadn't considered that.

For free 3D cloud-based software, I tried Onshape but found its user-interface brutal. It's dumbed down so much you can't figure out or find basic instructions and the metaphors, grouping of commands is so bad I laughed so hard at how dumb the software left me.

Yes, there are many choices for "baby's first CAD" but you will find the limits quickly. I use freecad and openscad. Others like fusion360 among others, I found that it ran super slow on my machine. Also, recently the authors limited what the community version is allowed to do, so if you learn their system, you may find yourself in a situation subject to the whims of the company.

If you want examples of either, I have released all the source files of designs I have released. Some of them are "remixes" of existing STLs, which might be less interesting though. https://www.thingiverse.com/clearchris/designs

[redwire]

Re: Signal Tracer - Requesting input on requirements

Before, I used a mono 3.5mm jack and some leads with alligator clips. This works but noisy with high impedance circuits and probing with an alligator clip can short stuff out on a board.

Adding the BNC - I found a scope probe great for poking around equipment. It's shielded cable so no hum and noise picked up, and the tip or clip handy, no accidental slips. The X10 I can use if high voltage up around 300V or more if you have guts.

For free 3D cloud-based software, I tried Onshape but found its user-interface brutal. It's dumbed down so much you can't figure out or find basic instructions and the metaphors, grouping of commands is so bad I laughed so hard at how dumb the software left me.

[eccerr0r]

Re: Signal Tracer - Requesting input on requirements

Make sure you have enough hard edge free surfaces inside your case so you'll less likely get resonances, heh. Then also trying to increase the effective air volume in the path so you can get better bass response too...

One thing I hate about 3D modeling is having to build a component library just like any other CAD... or is there a library of existing components somewhere?

Currently using OpenSCAD at the moment with Cura as my slicer. Talk about obscure CAD programs, that even less likely has libraries available.

FreeCAD looks intimidating. I don't quite get how to move and make pieces around yet. And then attaching pieces together...

[clearchris]

Re: Signal Tracer - Requesting input on requirements

What hardware and software are you using for the enclosure 3D printing and design?
P.S. I would have an on/off LED so the battery doesn't go dead.

Freecad. If you download it, get the hidden weekly build, don't use the big download button. Don't bother attempting to use it before you watch some tutorials.

For slicing (translating from design to 3d printer gcode) I use SuperSlicer.

Yeah, I was working getting an LED placed on the front panel today.

I'm printing this on a monoprice select mini. It's a good first printer, but it's very small. The new hot starter printer is the Ender 3.
https://www.monoprice.com/product?p_id=15365

My other printer is a beast, Tronxy x5sa-400. Not a starter printer, I had to print a few pieces just to get it assembled.

TBH may well just use a ⅛" phone jack as input instead of BNC, since these frequencies are so low that you don't have to worry too much about connector discontinuities...?

But then it'd look like a...speaker... instead of test equipment? heh.

Heh, I am putting an rca jack on the back so I can use it as a speaker, but it will still look like test equipment. But then again, it is going on my electronics bench, so it won't look out of place.

[eccerr0r]

Re: Signal Tracer - Requesting input on requirements

TBH may well just use a ⅛" phone jack as input instead of BNC, since these frequencies are so low that you don't have to worry too much about connector discontinuities...?

But then it'd look like a...speaker... instead of test equipment? heh.

[redwire]

Re: Signal Tracer - Requesting input on requirements

What hardware and software are you using for the enclosure 3D printing and design?
P.S. I would have an on/off LED so the battery doesn't go dead.