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Author Topic: Test Equipment: Oscillocopes  (Read 66924 times)

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #150 on: February 25, 2015, 05:01:00 AM »
Yes, that calibrator trace does look a little funky. It should be more level across the tops and bottoms. I presume you have adjusted the probes for the squarest-flattest possible display as per the instructions.  Did you say at one point that you found some voltages that were off-spec in the calibrator circuit? The spec on the calibrator output is 300 mV plus or minus one percent at normal temperatures. So this should produce a flat, horizontal  top and bottom parts of the square wave output. It looks like the output voltage is sagging a bit in the pulses, or at least the display of them is. Now is when you'd like to have a good external square wave generator, and/or another scope,  to see if the problem is in the calibrator or somewhere else in the scope! If the "known good" square wave generator gives you a good flat-topped trace then you know that it is the calibrator sagging, but the scope itself is displaying correctly.

As to the voltage asymmetry: Since you are in AC-coupled input mode I would expect the displayed trace to be more symmetrical about the zero-baseline even if the calibrator signal itself isn't perfectly symmetrical. This may be a "DC bias" issue, which is an internal adjustment that you will come across when you run through the performance checks or calibration procedures. Again, it would be nice to see what happens when you display other signals that are known not to have any DC offset. Have you tried looking at the GenRad oscillator's sine wave output yet? If that instrument is working properly it should be giving a symmetrical sine wave.


I don't know if you have the short "operator's manual" in addition to your SM. I'm attaching it below just in case you don't have it. It has lots of instructions for making the various measurements that are possible with the scope. (It also includes instructions for the DMM option which you don't have, obviously.)

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Re: Test Equipment: Oscillocopes
« Reply #150 on: February 25, 2015, 05:01:00 AM »

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #151 on: February 25, 2015, 05:13:05 AM »
Ah.... do you have the probes in 1x or 10x attenuation? I just noticed that my Tek 2213a does the same thing if I have the probes set to 1x instead of 10x and only when AC-coupled. When DC-coupled the traces flatten out nicely.  The cal trace slopes in exactly the same way yours is doing when I use 1x probe atten and AC coupling.

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #152 on: February 25, 2015, 07:09:01 PM »
OK, I've made a short video that I think accounts for both issues: the sloping trace and the voltage asymmetry. At least it accounts for those symptoms on my Tek 2213a, and I think that the same thing is going on with the 465 as well.

My Tek 2213a shows the same thing when the probe is set to 1x attenuation and the channel is AC-coupled. Also,when the probe is set to 1x, the compensation capacitor adjustment has almost no effect on the shape of the trace. When set to 10x attenuation the probe compensation can be adjusted as per the instructions in the probe manual.

When DC-coupling is selected with 1x attenuation, the sloping of the calibrator trace goes away. When the probe is set to 10x attenuation, there is no sloping in either AC or DC coupled input.

The voltage asymmetry around the zero volt baseline when AC-Coupled is due, _I think_, to the slight time asymmetry, or duty cycle, of the calibrator signal. Since  the AC coupling brings the average of the trace down to the zero baseline, it is the _areas_ of the positive and negative going parts of the "square" waveform that are averaged. The narrower (shorter duration) part of the pulse waveform will have a slightly higher peak value than the wider part.

http://www.youtube.com/watch?v=HmHRdh8OnUw

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Re: Test Equipment: Oscillocopes
« Reply #152 on: February 25, 2015, 07:09:01 PM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #153 on: February 25, 2015, 10:24:20 PM »
Ah.... do you have the probes in 1x or 10x attenuation? I just noticed that my Tek 2213a does the same thing if I have the probes set to 1x instead of 10x and only when AC-coupled. When DC-coupled the traces flatten out nicely.  The cal trace slopes in exactly the same way yours is doing when I use 1x probe atten and AC coupling.
Yes, I did have the probes on 1X attenuation.

Quote
OK, I've made a short video that I think accounts for both issues: the sloping trace and the voltage asymmetry. At least it accounts for those symptoms on my Tek 2213a, and I think that the same thing is going on with the 465 as well.

My Tek 2213a shows the same thing when the probe is set to 1x attenuation and the channel is AC-coupled. Also,when the probe is set to 1x, the compensation capacitor adjustment has almost no effect on the shape of the trace. When set to 10x attenuation the probe compensation can be adjusted as per the instructions in the probe manual.

When DC-coupling is selected with 1x attenuation, the sloping of the calibrator trace goes away. When the probe is set to 10x attenuation, there is no sloping in either AC or DC coupled input.

The voltage asymmetry around the zero volt baseline when AC-Coupled is due, _I think_, to the slight time asymmetry, or duty cycle, of the calibrator signal. Since  the AC coupling brings the average of the trace down to the zero baseline, it is the _areas_ of the positive and negative going parts of the "square" waveform that are averaged. The narrower (shorter duration) part of the pulse waveform will have a slightly higher peak value than the wider part.

http://www.youtube.com/watch?v=HmHRdh8OnUw

The 465 acts exactly the same as your 2213A in these aspects.
Definitely very helpful information.  Not even the scope manual nor the probe manuals from Tek specified anything at all about them having to be on 10x and DC coupling in order to properly adjust the compensation cap.

One issue I have noticed with these Chinese probes is that the scope does not automatically detect whether I have it set on 1X or 10X.  I seriously doubt it, but are all these fairly cheap Chinese probes this way?  If not, I would have to say that I do not recommend them to anyone. These ones are the model "PP-200", although the seller's listing did not specify this at all. If I would have bothered to ask them, I'm sure they would have had no choice but to tell me.  They said that they have never had any returns, though, and they have 100% feedback and all that jazz.  Seems that really doesn't mean all that much these days.  Do you think that possibly the reason why it doesn't recognize the attenuation setting on these cheap probes is because it is so old?
Is there any way for me to manually change what attenuation the scope shows, so I can match the display to the probes?  I don't really know if this is particularly necessary, since the screen shows exactly the same trace with the cheap ones as it does with the 6062A and 6065A. The only real difference is that the indicator light at the V/DIV knob doesn't change.

There does seem to be a few other quirks with this scope as far as what the screen shows when the settings are not set for the trace to appear entirely on-screen.  At this point, I'm not too concerned about it since, well, who really would want any part of their trace to appear off screen??? And maybe in time after some use, the rest of whatever gunk/oxidation remains inside of the pots and switches will work itself loose with the deoxit that is in there still. If not, here in a few weeks maybe I'll put a drop of WD40 or PB in each one and let 'er sit for a few days and see where it stands then. (of course after I try putting some deoxit and WD/PB in an old pot I have laying around and testing it several times to make sure it doesn't cause any issues/shorts/etc)

Anyway, what are your thoughts on the attenuation sensing w cheap probes issue?  Just keep it in mind and keep on rollin along the knowledge superhighway?

Brian

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #154 on: February 25, 2015, 11:29:54 PM »
Ok, so it appears that I still have a fair amount of "noise" and bad contacts on channel 2. 

-I did a quick test with an old pot similar to the ones used in the scope:
-I hooked it up to my DMM on the Resistance setting, and observed how smoothly/roughly it functioned without any treatment. It was OK, but not all that great. It had quite a fair amount of 'noise', meaning that the R value would jump around a bit while adjusting, instead of smoothly increasing or decreasing.
-I left it connected, and put a couple drops of Deoxit on the shaft and let it seep in for a minute, then slowly adjusted and observed. This created a good bit of "extra noise" in the pot, and what I mean by this is that, when adjusting the pot, the resistance would 'jump' up to 2x or even 3x of the overall R value of the pot. It would immediately settle to where it should be upon stopping rotation.
-I let it sit for a couple minutes and repeated, with close to the same results, but a little less 'jumping'.
-I then put a single drop of PB blaster on the shaft and let it seep in. Waited a couple min, then repeated the adjusting/observing process.  It continued to do the same thing ('jumping' effect) but a little less frequently.
-After sitting for approx 10 minutes, still connected and DMM powered on, while adjusting the pot I get absolutely no 'jumping' and the pot works almost flawlessly, and much, much better than it did before any treatment.  Another 10 minutes, and I am noticing that it is jumping again, but only by about 300 ohms, and only occasionally. It seems to be occurring in about the same positions, though, which I would think might be grime that has settled on the contact surface after the PB has ran off.

I am going to set this pot aside and see how it performs later, check for any shorting, "noise", etc.  I am also going to take a similar pot and do the same but without the PB Blaster.  Then after several hours or so I am going to rinse them out with IPA and see if their performance changes.

I am thinking that, since I still have a fair amount of 'noise' in some of the pots on my scope, I may take the cover and the knobs off and put a drop or two of PB Blaster in them, work it in by turning, let it sit overnight, and then rinse them all out with IPA twice and let them dry out before I power it up again, and see if it's any better.  I just don't think the Deoxit is up to the task in it's entirety (of course I will find out for sure if I can find another old pot that is close to the same as the one I just tested). Not to mention it's only D5, not the PowerBooster stuff that is actually a cleaner instead of mostly conditioner.  Plus I think it would be smart to rinse out the cleaner and loose gunk, anyway. Hopefully that FINALLY solves the rest of my "noise" issues once and for all!!!

Oh, and for everyone who might not know, PB Blaster is the pro-grade equivalent of WD40. PB = "Penetrating Blaster".  It's somehow also made to attract to rust and ferrous metals so it will free up heavily rusted and/or stuck parts. Just a little heads-up in case some of you end up being in need of something like that when your WD40 can't handle the task.

If, after the overnight PB/IPA rinse treatment, she's still got issues with CH2, I will make a vid showing what's happening. I just wish I had a tripod so I don't give you all nausea having to watch my shaky vids....

Brian

Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #154 on: February 25, 2015, 11:29:54 PM »
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Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #155 on: February 26, 2015, 12:02:39 AM »
OK, so we have the issues relating to the calibration trace sorted, then, I hope. Nothing is wrong, it's normal behaviour when looking at the Calibrator signal with a 1x probe and AC-coupled input. The probe compensation should be adjusted with the probe in the 10x position, and normally you will be using 10x probe setting and DC-coupled inputs in most cases anyway.


You do realize that you will void your factory warranty by using that "blaster" stuff on your scope, I hope....    ;)

Seriously... I don't think that any form of petroleum solvent is a good idea to use. Who knows what kind of residue they  might leave behind, or what they might dissolve in there. Stick with the commercial contact cleaners specifically made for the purpose. That's just my two cents worth.


As far as the probes go... No, none of these aftermarket probes that are "inexpensive" have the hardware for the scope to detect the attenuation setting. You may note on the actual Tek probe you have that there is a little pin next to the BNC connector. This is the "readout pin" that makes contact with a ring around the base of the BNC connector on the scope chassis, and this is what tells the scope what attenuation setting you have on the probe, according to the switch setting on the probe.

When using a probe that does not have the readout pin and its internal wiring, you just have to remember the atten setting and look at the right number on the V/div scale. That is, you use the knob value that is over the "10x" or "1x" indicator light, appropriately.

Most of the time you will be using 10x attenuation anyway. When you use a 100x probe then you need to multiply the 10x indication by 10 again.

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #156 on: February 26, 2015, 12:34:29 AM »
Ah ok, good to know.  I didn't realize that the little pin is what tells the scope to switch the light from 1X to 10X.  That is really all it's doing on this scope, correct?

I just did a little experiment with a few slider pots that I had from an old stereo, and noticed that even the high quality Deoxit doesn't actually "remove" really any of the gunk from it, and only removes a very small amount when it is "flushed" after a min or so. When I loosened the gunk up with Deoxit, and then put a little PB on it, the gunk immediately came off when I blotted it with a paper towel. Afterwards, it appears the IPA rinse removed all of the PB and Deoxit and left the slider nice and clean, and functioning way, way, way better than the "control" slider and also the Deoxit slider both with and without rinsing.

HAHAHA Factory warranty.... I WISH!  If only, if only............ 

What then about your comment regarding the use of WD40 on badly oxidized/dirty switch contacts before? Both PB and WD have the same petroleum distillate as their main ingredient.  However, I guess there is a bit of a difference between using it on an exposed and easily accessible part and an enclosed pot... I really do not want to be taking the back cover off of each of these pots to clean them out. who knows if I would ever get them back together if there's a spring in there that decides to shoot all the parts out in my face.. 
I guess if this D5 just isn't cutting it, I should try and locate some kind of better contact cleaner. The manual does specifically say not to use petroleum ether products to clean anything. I guess I'll just have to try Grainger for some aerospace contact cleaner, or order something. What would you suggest?
I still think it may be a good idea to rinse the pots out afterwards with IPA, what do you think?
Never mind, It seems the more I work the knob back and forth, the less "noise" I get. I'll just sit here and change the settings repeatedly for a while until it's no longer noticeable!

It's mainly the CH2 coupling switch under the V/DIV knob giving me trouble still, but it's also the position knob. All the other knobs/switches seem to be working fine now.

Also I just want to add that I definitely needed to adjust the tuning capacitor on the probe when I moved it from CH1 to CH2, so, like you stated, it is definitely necessary to adjust them when moving them from one channel to another, at least on my scope.

On another note, for the Arduino LCD I remember you saying that the Parallax one is the best because it only takes up a few spaces on the duino's output.  Well, I think I've found out how to make that with a generic LCD and an I2C chip. Check this out and let me know if you think it's a good way to go.
http://electronics-diy.com/two-wire-i2c-arduino-lcd-display.php

Brian

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Re: Test Equipment: Oscillocopes
« Reply #156 on: February 26, 2015, 12:34:29 AM »
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Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #157 on: February 26, 2015, 01:39:23 AM »
Yes, the readout pin just tells the scope to switch the indicator light. It doesn't do anything else in the scope.

No, that wasn't me who suggested the WD-40 before, I think it was Pirate. If it works, great. If it screws up your pots and switches... then what are you gonna do?
Just don't get any on those special attenuator boards, the SM specifically warns against that.

Yes, the Parallax LCD has some kind of serial interface wired in to give it the 1-data-line capability. There is an Arduino library of function calls for the Parallax LCD using its interface. I don't know if this will also work with your chip+generic LCD. You may have to write your own library functions for it! There are many libraries for the various LCD types, see the "playground" link below.

Ah... I see that the link you provided has already taken care of the necessary I2C libraries, that's great! The I2C uses 2 wires and the Parallax only one, but sure, it seems like a good project to try. Probably a lot cheaper than the Parallax LCD too. But no speaker.

http://arduino.cc/en/Reference/LiquidCrystal?from=Tutorial.LCDLibrary
http://playground.arduino.cc/Code/LCD   (scroll down for the Parallax 3-wire LCD library)

Offline Pirate88179

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Re: Test Equipment: Oscillocopes
« Reply #158 on: February 26, 2015, 02:06:37 AM »
I don't think it was me suggesting WD-40 for the pots on a scope.  I used that trick suggested by AllAmerican5 Radio (Youtube) for treating the pot on my old Triplett meter but I don't think I would risk that on anything inside my scope.  It does sound like something I might suggest though.

Bill

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Re: Test Equipment: Oscillocopes
« Reply #158 on: February 26, 2015, 02:06:37 AM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #159 on: February 26, 2015, 02:23:52 AM »
[quote author=TinselKoala link=topic=15536.msg440014#msg440014 date=1424911163
Ah... I see that the link you provided has already taken care of the necessary I2C libraries, that's great! The I2C uses 2 wires and the Parallax only one, but sure, it seems like a good project to try. Probably a lot cheaper than the Parallax LCD too. But no speaker.

http://arduino.cc/en/Reference/LiquidCrystal?from=Tutorial.LCDLibrary
http://playground.arduino.cc/Code/LCD   (scroll down for the Parallax 3-wire LCD library)
[/quote]

I didn't know the 3-wire had a speaker as well.  Oh well, the 4-wire generic will have to do for now. Once I know what else to get from Digikey or one of the others I'll grab up one or two of those chips.  I'd get the Parallax, but I can think of quite a few other things that I'd rather put $40 towards, like a good power supply, a FG, Variac.....
I dug out my old vid cam earlier and found a mount for a tripod, so now all I need to do is find the cable to connect it to the PC and get or make a tripod, and I'll be able to stop nauseating people with my shaky vids

Offline MileHigh

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Re: Test Equipment: Oscillocopes
« Reply #160 on: February 26, 2015, 02:44:22 AM »
Brian:

I hate to tell you this but in my opinion you made a mistake using the PB Blaster.  That is noxious stuff for eating through rust to take nuts off of bolts and stuff like that.  That stuff even smells like it means business.  I know it from the brand "Screwloose."  The WD40 is safely assumed to be essentially benign.  Who knows, but potentially the PB Blaster could eat through the carbon or plastic resistive track inside a pot over several months.  It's simply nasty stuff if it looks and smells like I think it does.

MileHigh

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Re: Test Equipment: Oscillocopes
« Reply #160 on: February 26, 2015, 02:44:22 AM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #161 on: February 26, 2015, 03:01:39 AM »
Brian:

I hate to tell you this but in my opinion you made a mistake using the PB Blaster.  That is noxious stuff for eating through rust to take nuts off of bolts and stuff like that.  That stuff even smells like it means business.  I know it from the brand "Screwloose."  The WD40 is safely assumed to be essentially benign.  Who knows, but potentially the PB Blaster could eat through the carbon or plastic resistive track inside a pot over several months.  It's simply nasty stuff if it looks and smells like I think it does.

MileHigh

I haven't used it on anything but the one slider that I did the experiment with.  That is exactly why I did it on something that doesn't matter, and brought it up in the forum before using anything like that on something that does matter, like the scope. :)

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #162 on: February 26, 2015, 03:18:27 AM »
There must be an issue with using my computer to put a signal to the scope....
For some reason, the 465 displays the exact same trace no matter what signal I output from my PC. This is the case whether I connect the probe to Left, Right, or Ground. The sounds change in the headphones I wired in, and on proper channels and all that.
If I hook up the 'ground' to the ground out of the PC, it cancels out the signal.
What I see when I hook it to the PC out is a crappy looking sine wave trace at 150V.

I tried various different settings - AC and DC coupling show the same trace.
Trigger level does nothing.
Anything but "A" on Horizontal Display makes it extremely bright except for the first half of the sine wave.

I didn't bother switching to one of my Tek probes to see if the sine wave trace looked any better. seems pointless to do.

I also disabled all audio enhancements and DC offset cancellation, etc. It should be 'direct output'.
About to make a quick video to show what I am talking about, then I'm going to figure out how to use the GR Oscillator and see what that looks like on the scope.
https://www.youtube.com/watch?v=E9l-EnME9Vw

Brian

Offline Pirate88179

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Re: Test Equipment: Oscillocopes
« Reply #163 on: February 26, 2015, 03:23:01 AM »
There must be an issue with using my computer to put a signal to the scope....
For some reason, the 465 displays the exact same trace no matter what signal I output from my PC. This is the case whether I connect the probe to Left, Right, or Ground. The sounds change in the headphones I wired in, and on proper channels and all that.
If I hook up the 'ground' to the ground out of the PC, it cancels out the signal.
What I see when I hook it to the PC out is a crappy looking sine wave trace at 150V.

I tried various different settings - AC and DC coupling show the same trace.
Trigger level does nothing.
Anything but "A" on Horizontal Display makes it extremely bright except for the first half of the sine wave.

I didn't bother switching to one of my Tek probes to see if the sine wave trace looked any better. seems pointless to do.

I also disabled all audio enhancements and DC offset cancellation, etc. It should be 'direct output'.
About to make a quick video to show what I am talking about, then I'm going to figure out how to use the GR Oscillator and see what that looks like on the scope.

Brian

I would like this to be figured out as well.  I never thought of hooking up my scope to "see" the music I play on my computer all of the time.

I didn't know we could do that.

I also do not know how to do that.

If it is as easy as probing the 3.5mm output cord from my computer then, it will be easy.  Somehow, I don't think it is as simple as that.  I will keep watching here to find out how to do this.

Bill

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #164 on: February 26, 2015, 03:50:50 AM »
I would like this to be figured out as well.  I never thought of hooking up my scope to "see" the music I play on my computer all of the time.

I didn't know we could do that.

I also do not know how to do that.

If it is as easy as probing the 3.5mm output cord from my computer then, it will be easy.  Somehow, I don't think it is as simple as that.  I will keep watching here to find out how to do this.

Bill

It appears that the PC headphone jack is outputting an AC signal in order to power the headphones that overpowers any waveforms from the audio that I would be able to see on the scope.  Therefore it is necessary to run the PC output signal into some sort of "filter device" in order to kill the main power signal and only leave the audio waveform. 
Now that I think about it...  The output signal from the PC is an ACTIVE signal, in order to power the unpowered listening devices (headphones).  The signal that is needed in order to watch the waveforms on the scope is a PASSIVE signal.  So now, to look up how to transform an active signal to a passive signal..  Usually it's done the other way around via amplifier..

I'm no audio expert by any means, so I could be completely wrong about that. I could be doing something wrong, or it could be something entirely different.  We'll just have to wait and see what solution is brought forth by people who know more about this.

Brian


**There must be something that I'm missing as far as the whole "150V" thing....  My probe was on X10.... but I don't see how my PC could POSSIBLY be pushing 150VAC out the headphone jack... maybe 15V but more likely 1.5V.  My scope MUST have been being deceived, somehow.  The loopback to the PC scope only showed 1.2V, but that's internal loopback via software, so I don't see how that would apply whatsoever to what comes out of the audio jack. 
I've been searching "Active to Passive signal conversion" and coming up with junk for 3D video projection and nothing for audio, which tells me that I'm missing something very simple.  All in all, a bit confused.... Maybe an Arduino based FG is going to be a better way to go...**

 

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