Signal Tracer revisited.......

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Janitor Tzap
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Signal Tracer revisited.......

Post by Janitor Tzap » Wed Oct 21, 2009 7:20 pm

numb3rs question got me to thinking about putting together a simple inductive signal tracer.

So, I dug around the web to see what sort of designs I could find.
http://www.electronics-project-design.c ... atics.html
This design is pretty simple, with 1458 dual op-amp.

But where can I find a 1.25 long by 0.25 in diameter Ferrite Rod?
Also, the low impedance headphones are kind of hard to find now a days.
I'm wondering if I could use an 8 ohm speaker?
Or maybe a speaker that is on one of those musical gift cards?

I want to place the circuit into a hand held box: 4" to 5" long by 1 1/2" wide by 1" deep.


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Re: Signal Tracer revisited.......

Post by CeaSaR » Wed Oct 21, 2009 7:55 pm

Hey Janitor Tzap,

That is the one I was thinking about when I posted my question to numb3rs. Now all you need is
the signal injector side of the project and it will be complete. Time to look through the back issues again.

CeaSaR
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Janitor Tzap
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Re: Signal Tracer revisited.......

Post by Janitor Tzap » Wed Oct 21, 2009 8:12 pm

CeaSaR wrote:Hey Janitor Tzap,

That is the one I was thinking about when I posted my question to numb3rs. Now all you need is
the signal injector side of the project and it will be complete. Time to look through the back issues again.

CeaSaR
I've got two signal injectors already.
One is a 1Khz injector probe for audio work.
And an Oscillating Toner "Fox" Unit.

Normally this "Fox" Toner Box would be with its "Hound" Signal Tracer.
But, I found it sitting by itself on a surplus shelf with a $2.00 price tag on it.
So, it was to good a deal to pass up. :grin:


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Bob Scott
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Re: Signal Tracer revisited.......

Post by Bob Scott » Wed Oct 21, 2009 11:01 pm

Janitor Tzap wrote:But where can I find a 1.25 long by 0.25 in diameter Ferrite Rod?
A scrap AM radio? A dealer of Amidon parts might have their ferrite rods.
http://www.amidoncorp.com
Also, the low impedance headphones are kind of hard to find now a days.
I'm wondering if I could use an 8 ohm speaker?
Try any speaker to see if it is loud enough, but there is an optimum impedance for the load. The 1458 goes into current limiting at 20mA of output current. The ideal speaker or phone for getting the most loudness would be one that draws 20mA peak at the max peak output voltage of approximately +/-4V. That would be 4/.02 = 200 Ohms. (R=/V/I) The "low impedance headphone" requirement is misleading.
-=VA7KOR=- My solar system includes Pluto.

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Re: Signal Tracer revisited.......

Post by Janitor Tzap » Mon Oct 26, 2009 12:49 pm

Bob,

Thanks for the tip. :smile:

I went out to the local thrift store and found a junk AM/FM Radio that I can use.
Only paid a buck for it.
I wish it wasn't missing it's battery door, other wise it would be perfect for housing the circuit. :mad:
It also has a speaker built into the case, and mini-slide switch which I may be able to use too.

Well, I'll keep working at it, and post a progress report later.


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Re: Signal Tracer revisited.......

Post by Bob Scott » Mon Oct 26, 2009 5:25 pm

Janitor Tzap wrote:Thanks for the tip. :smile:

I went out to the local thrift store and found a junk AM/FM Radio that I can use.
Only paid a buck for it.
That's cool. The closest ferrite rod for AM Radio in type 61 ferrite material from Amidon is $4.00, and it's 1/4" X 2". You got a bargain in comparison.
I wish it wasn't missing it's battery door, other wise it would be perfect for housing the circuit. :mad:
I guess that is why it was only a buck. :grin:
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Re: Signal Tracer revisited.......

Post by CeaSaR » Mon Oct 26, 2009 7:35 pm

Janitor Tzap,

Now that is truly Recycled Electronics! :cool:

CeaSaR
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Re: Signal Tracer revisited.......

Post by sofaspud » Tue Oct 27, 2009 4:07 pm

Does your "new" radio include a LM386 chip? For driving a speaker, I think I'd use it instead of the
1458. I'm not sure what kind of output the 1458 can deliver to a loudspeaker, but it's probably not
much. The circuit as is provides about 300X amplification; the LM386 can give 200X with a simpler
circuit. If more than 200X is needed, R1 can be changed to 4.7kohms and the LM386 circuit can
replace everything after C2. That'll provide about 400X and easily drive an 8 ohm speaker.

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Re: Signal Tracer revisited.......

Post by Janitor Tzap » Wed Oct 28, 2009 8:45 pm

sofaspud,

Yeah, that's an idea too.
But I rummaged through all my IC's, and of course I don't have any LM386's.
But I have half a dozen 1458's.

This little radio had only 2 IC's in it.
One was the AM/FM Demodulator.
The other is a strange SIP amplifier IC.
I'm thinking that maybe I should use that amp if the 1458 can't drive the 8 ohm speaker.
I'm going to re-use the PC board out the radio for mounting the circuit into.
The PC board is already designed to fit in the case.
So, that saves me a lot time, trying fit and mount in a new board.
Thou...
I will be cutting some traces, and running some jumpers on the board.


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Re: Signal Tracer revisited.......

Post by sofaspud » Thu Oct 29, 2009 3:58 am

Utilizing the radio's existing circuitry is a good plan. I'm not dead set on the LM386. I'd just tap into the
already-built-and-wired volume control/amp/speaker of the radio. If the 1458 has a 40mA output source
capability (my datasheet neglects to include this spec), using I^2R gives a measly 12.8mW into an 8 ohm
speaker. Decent enough for driving headphones, and I'm guessing that Mr. Rakes chose that because it
does tend to increase the sensitivity of the instrument, at least from the user's perspective, and does so
with a minimum of parts.

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Re: Signal Tracer revisited.......

Post by Janitor Tzap » Sat Feb 20, 2010 6:24 pm

Well, as promised I have a progress report on this project.

First off....
After much searching and not finding any info about the SIP IC Amplifier chip.
{And the fact that the radio circuit was running on 3Vdc instead of 9Vdc.}
Kind of put the brakes on using it for the speaker.
Thus, I found a LM386 at Radio Shack for $1.50 that I could use instead.

So, I stripped off all the components from the old radio's PC board.
Started working rewiring and traces.
But this had it own headaches, with cutting traces and routing wire jumpers.
Plus, I was going to use the 50k Volume control & On/Off switch.
But the 50K Pot was to high and sensitivity was poor.

Ok, scratch using the old PC Board and Vol/On/Off control.
Well it was back to Radio Shack again for a Perf-Board $2.00.
Now I worked out the mounting of the Perf-Board inside the case.
As well as the mounting of the 10K Volume control and the On/Off switch.
Then mounted the IC's and the rest of the components.

I then tested the it with my 1Khz signal injector.
It picks up the signal loud and clear.

Now for the M77 Tracer Unit 800hz warbler.
Nothing.

Heres the circuit.
Image
Any idea's why it won't pickup the 800hz Signal?


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Re: Signal Tracer revisited.......

Post by Robert Reed » Sat Feb 20, 2010 9:14 pm

Vastly different output levels?

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Re: Signal Tracer revisited.......

Post by sofaspud » Sat Feb 20, 2010 9:47 pm

That's also what I'm thinking. There's not much difference between 1kHz and 800Hz, relatively speaking. "Warbler", too, implies
a multi-tone output; I'm not familiar with the M77 Tracer Unit. That aside, C4 could be disconnected from pin 7 and probed at
pins 2, 1, and 6. The LM386 is spec'd for <1Vp-p input. Overdriven, it might refuse to output anything meaningful to the speaker.

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Re: Signal Tracer revisited.......

Post by MrAl » Sun Feb 21, 2010 6:21 am

Hi,


I am not sure if you are aware of this or not but, those 0.1uf caps have a significant impedance
when used with 1k and 3.3k as those two resistors R1 and R4 are. That shouldnt stop it from
working but will decrease the amplitude for low frequencies.
Maybe 1uf caps would be better.
LEDs vs Bulbs, LEDs are winning.

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Re: Signal Tracer revisited.......

Post by Janitor Tzap » Sun Feb 21, 2010 11:04 am

sofaspud wrote:That's also what I'm thinking. There's not much difference between 1kHz and 800Hz, relatively speaking. "Warbler", too, implies
a multi-tone output; I'm not familiar with the M77 Tracer Unit.
Yes, in oscillates back and forth from 800hz to 850hz.
That aside, C4 could be disconnected from pin 7 and probed at
pins 2, 1, and 6. The LM386 is spec'd for <1Vp-p input. Overdriven, it might refuse to output anything meaningful to the speaker.
Hmmm.....
The signal output of the M77 is a 3Vp-p square wave.
The signal output of my 1Khz signal injector is 4Vp-p triangle wave.
So, I'm thinking it's more a sensitivity problem.
MrAl wrote:Hi,


I am not sure if you are aware of this or not but, those 0.1uf caps have a significant impedance
when used with 1k and 3.3k as those two resistors R1 and R4 are. That shouldnt stop it from
working but will decrease the amplitude for low frequencies.
Maybe 1uf caps would be better.
Hmmm........
That is a good point MrAl.
I wonder if the .1uf for C1 & C2 was a miss print in the schematic.
I'll try a 1uf caps and see if that helps.

It is strange thou.....
I bread boarded the circuit first to make sure it worked, and used my 1Khz injector for testing it.
I didn't think to try the M77 Tracer at that time.

Thanks!


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