Barracuda Legend Kit Problems

[ivconic]

I seem to have had some "fat finger trouble" (FFT), as your calculation is correct. Must have hit too many buttons at once to get 0.0267.
Also, 127,000 * 0.0267 = 3390 (not 7209) ... I certainly cocked that up!

So, with the correct values (thanks Green - at least someone was awake) we have 127,000 * 0.0256 = 3251. Which means that a 1uV signal at the input results in 3.25mV at the output.

Hopefully it's right this time.

Too much simulators ... and there what you get !
Leave simulators and took soldering iron in your hands instead.
Feel the heat!

[Qiaozhi]

I get a sampling gain of .0256(640 x .000040). What is the correct formula?

I seem to have had some "fat finger trouble" (FFT), as your calculation is correct. Must have hit too many buttons at once to get 0.0267.
Also, 127,000 * 0.0267 = 3390 (not 7209) ... I certainly cocked that up!

So, with the correct values (thanks Green - at least someone was awake) we have 127,000 * 0.0256 = 3251. Which means that a 1uV signal at the input results in 3.25mV at the output.

Hopefully it's right this time.

[Michaelo]

I think it's been mentioned before but there's no actual pre-amp, it's just a single stage high gain amplifier (gain = 1,000).
The remaining circuitry deals with the manipulation of the resultant signal, basically audio...
A pre-amp (with decent filtering) would be a welcome change...

[green]

The preamp has a gain of 1000, and the 1st integrator stage has a gain of 270. So the total gain is 270,000.
However ... you must also include the sampling gates.
With a TX pulse rate of 640, and a sampling pulse width of 40us, the sampling process has an effective gain of 0.0267.
Hence we have: 127,000 * 0.0267 = 7209. In this case, a 1uV input will result in a 7.2mV output.

I get a sampling gain of .0256(640 x .000040). What is the correct formula?

[6666]

Here u go.. Top trace is pin 2. Bottom is pin 4.
Sweep = 50uS/ div
Y axis is 2V/ div.

Pulse is essentually returning to ground from -5V. I have my scope ground reference on the minus lead of C1.

Just looked at my bara pulses, pin 2 pin4 and mine are nice and clean like Dons, remember that - Batt is ground for P Fet.

[Impulse]

Hey all the barracuda is in the post! hopefully we will get to the bottom of the issues we have had

[Old cart]

The signal chain ends at the output of the first stage, and after that the signal must be above the threshold to generate an audio tone. So the second stage only serves to boost the audio amplitude. In other words, if you increase the gain in the first stage you will increase sensitivity, albeit with an increase in instability. If you increase gain in the second stage, you will boost the sensitivity of the audio to a signal that exceeds the threshold.

Of course, don't know how I can be so stupid! Thanks for setting this straight.

[Qiaozhi]

Yes but won't the audio then see that gain? That is the user interface element from coil, the headphone tone, would experience that gain.
I did not know how to calculate the integrator. Gain. Thanks.

The signal chain ends at the output of the first stage, and after that the signal must be above the threshold to generate an audio tone. So the second stage only serves to boost the audio amplitude. In other words, if you increase the gain in the first stage you will increase sensitivity, albeit with an increase in instability. If you increase gain in the second stage, you will boost the sensitivity of the audio to a signal that exceeds the threshold.

[Old cart]

The final stage just supplies the threshold and drives the audio stage.

Yes but won't the audio then see that gain? That is the user interface element from coil, the headphone tone, would experience that gain.
I did not know how to calculate the integrator. Gain. Thanks.

[Qiaozhi]

How about the final DC gain stage? Does that not count?

The final stage just supplies the threshold and drives the audio stage.

[kt315]

How about the final DC gain stage? Does that not count?

270000x100 it is 27 000 000
who there told Bara is low sens unit?

[ivconic]

Ivconic, agreed. So would it not be better if we can make changes so more of the detectors perform well rather than just some?
Have you found your Bara's to be unusually sensitive to coil movement?

This circuit has a lot of gain, as I recall about 27 million. If this is right 37nV gives 1 volt of output.

Of course it would be better to improve it further.
All the time here i must admit i am not exactly sure how mentioned problem is manifesting?
Coil movements, especially fast and agile; will most probably provoke certain mum response at detector, important to emphasize is that this is so typical not only for Barracuda but also to majority of other detectors too.
Especially in closed environment. In my room almost all detectors are sensible to coil movements, due presence of various "industrial" hums and interferences.
To clear up this better; it would be really helpful to record short video on that.
Can anybody record few seconds on that?

[Old cart]

The preamp has a gain of 1000, and the 1st integrator stage has a gain of 270. So the total gain is 270,000.
However ... you must also include the sampling gates.
With a TX pulse rate of 640, and a sampling pulse width of 40us, the sampling process has an effective gain of 0.0267.
Hence we have: 127,000 * 0.0267 = 7209. In this case, a 1uV input will result in a 7.2mV output.

How about the final DC gain stage? Does that not count?

[raygdunn]

Rain stops play

Are you saying you used a ferrite rod for the field testing? If so it has to be magnet, it must attract iron.

I assumed a coil core would be magnetised, but checked with a compass and it seems it is not! Not being familiar with the term ceramic magnet, I googled and found ferrite and proceeded from there☺ (I've put a ceramic magnet on order)

I have since tried a small 10mm flat disc rare earth magnet. Good range, but no joy with the test, maybe the iron content was too significant.

Final plan was to put coil on a stick to distance it from me, then wave it around in garden, whilst adjusting the second sample pulse width. I lost two 40106 chips to that. At first I thought I'd shorted something, but now I suspect the increased 11.5V+ battery supply. (LiPo supply seemed to work fine on earlier days) I was very careful the second time, but still no audio output. When more spares arrive next week, I'll try ramping up the usual 9V bench supply to see what happens. I'll suspend tests, whilst I only have the one sound 40106!

What I have noticed is that one newly inserted 40106, created very small spikes at start and end of coil pulse on the sample control pulses. I'm pretty sure that wasn't the on recent tests. But I have seen it before. Oddly one chip did survive the garden test, then showed the three extraneous mini pulses. Note that that is with the mod in place, so all voltages should have been within the same 5V range.

Time to work on fitting out the electronics box, coil housing and rewind my dodgy spider coil I think.

Ray

[Qiaozhi]

This circuit has a lot of gain, as I recall about 27 million. If this is right 37nV gives 1 volt of output.

The preamp has a gain of 1000, and the 1st integrator stage has a gain of 270. So the total gain is 270,000.
However ... you must also include the sampling gates.
With a TX pulse rate of 640, and a sampling pulse width of 40us, the sampling process has an effective gain of 0.0267.
Hence we have: 127,000 * 0.0267 = 7209. In this case, a 1uV input will result in a 7.2mV output.