MPP Beach Rev-E - partial fail at STEP 6, TP 6,8,9,10

[Polymer]

MPP Beach Rev-E - partial fail at STEP 6, TP 6,8,9,10

I have gotten stuck at STEP 6 on George's test procedure.

TP6 Main sample delay is 10us ==> OK
TP8 Sec. sample delay EFE is 120us ==> should be round 100us, not sure if OK

TP9 Main sample pulse width looks rotten
TP10 Secondary sample pulse width, looks OK but maybe too wide @15us

Here is a picture of all four measurements.



What could be wrong here?

I have replaced the TI CD14538BE, no change to be seen.

[Qiaozhi]

MPP Beach Rev-E - partial fail at STEP 6, TP 6,8,9,10

I have gotten stuck at STEP 6 on George's test procedure.

TP6 Main sample delay is 10us ==> OK
TP8 Sec. sample delay EFE is 120us ==> should be round 100us, not sure if OK

TP9 Main sample pulse width looks rotten
TP10 Secondary sample pulse width, looks OK but maybe too wide @15us

Here is a picture of all four measurements.

[ATTACH]45599[/ATTACH]

What could be wrong here?

I have replaced the TI CD14538BE, no change to be seen.

I assume you have shorted pin 2 of PL5 to either pin 1 or pin 3, as the main sample pulse delay is correct at 10us. Have you also shorted pin 2 of PL6 to either pin 1 or pin 2, as stated in the Build Document?

The secondary sample delay is set by R32 (10k) and C18 (10nF), which gives 10E3 * 10E-9 = 100us. If you're not using components with a low tolerance (such as 1% resistors) it is conceivable that the secondary delay could reach 120us.
The main and secondary pulse widths should be identical, and are set by R35 (4k7) and C19 (2n2), which gives 4.7E3 * 2.2E-9 = 9.68us. However, D10 and D11 also have an effect on the timing such that the actual value will be higher than 10us.

If the R and C values are definitely correct, I would suggest fitting a 25k pot to PL6 to check if the sample widths can be adjusted.

[Polymer]

I assume you have shorted pin 2 of PL5 to either pin 1 or pin 3, as the main sample pulse delay is correct at 10us. Have you also shorted pin 2 of PL6 to either pin 1 or pin 2, as stated in the Build Document?

The secondary sample delay is set by R32 (10k) and C18 (10nF), which gives 10E3 * 10E-9 = 100us. If you're not using components with a low tolerance (such as 1% resistors) it is conceivable that the secondary delay could reach 120us.
The main and secondary pulse widths should be identical, and are set by R35 (4k7) and C19 (2n2), which gives 4.7E3 * 2.2E-9 = 9.68us. However, D10 and D11 also have an effect on the timing such that the actual value will be higher than 10us.

If the R and C values are definitely correct, I would suggest fitting a 25k pot to PL6 to check if the sample widths can be adjusted.

Thank you George!

Yes, I had shorted pins of PL 5 and 6. In the new following oscilloscope pics I have put in a pot on PL6 - the width IS adjustable.

I am using 1% resistors. I measured them all before placing. Same with capacitors except the tolerances are 2.5 to 10 %.

The main and secondary pulse widths are identical.

The shape of the main sample pulse width still looks unhealthy to me (TP9). Looks like something is awry here.

What is your take on this shape?

[Qiaozhi]

Thank you George!

Yes, I had shorted pins of PL 5 and 6. In the new following oscilloscope pics I have put in a pot on PL6 - the width IS adjustable.

I am using 1% resistors. I measured them all before placing. Same with capacitors except the tolerances are 2.5 to 10 %.

The main and secondary pulse widths are identical.

The shape of the main sample pulse width still looks unhealthy to me (TP9). Looks like something is awry here.

What is your take on this shape?


[ATTACH]45609[/ATTACH]

That definitely doesn't look right.
Are you sure you're taking the measurements with reference to the +ve battery terminal, which is treated as ground (0V) in this design?

[waltr]

If the third scope capture is on TP9 then it is not correct.
Re-check the parts installed around U10a. Ensure that D11 in not backwards, etc.

Use a good magnifier to look at the soldering. Ensure all solder is flowed well and no shorts.

The other scope captures look good.

[Polymer]

That definitely doesn't look right.
Are you sure you're taking the measurements with reference to the +ve battery terminal, which is treated as ground (0V) in this design?

Uh, oh - my mistake writing vs. TP2 in previous posts/pics. Mixing up 2 & 5 is a weird thing.

Yes, I am measuring vs. TP5 (ground, which is + of 12v supply)

[Polymer]

Problem solved!

Thanks George and waltr.

Now it looks right:

[waltr]

Problem solved!

Thanks George and waltr.

Now it looks right:

[ATTACH]45616[/ATTACH]

Great.
Looks good now.
What was the problem and fix?

[Polymer]

Great.
Looks good now.
What was the problem and fix?

The J-FETS were "bogging" down the signal. Mine had different pinouts, so were incorrectly inserted.

[waltr]

The J-FETS were "bogging" down the signal. Mine had different pinouts, so were incorrectly inserted.

Ahh... I had the same problem on my first PI detector build. Forget to check the pin out of the JFETs I bought verse the ones I designed for.

Anyway, good find. How are the remaining steps going?

[kt315]

guys you have to check every thing you want to solder. look on this 1N4148 http://ipic.su/img/img7/fs/CIMG6473.1551391622.jpg

[waltr]

guys you have to check every thing you want to solder. look on this 1N4148 http://ipic.su/img/img7/fs/CIMG6473.1551391622.jpg

That is a good one kt and would have been very hard to find once soldered in.

[Polymer]

Ahh... I had the same problem on my first PI detector build. Forget to check the pin out of the JFETs I bought verse the ones I designed for.

Anyway, good find. How are the remaining steps going?

Here's a jfet data sheet that is made by mischievious ... errrr, data sheet makers - at least that's how I see it.
I found this one difficult to decipher at a glance, it's prone to misreading ... could have been done better.


Thanks for asking waltr. The detector is working, but there are few things that I am not too sure about and have me doubting:

Step 3 Tx oscillator:
The frequency is relatively unstable compared to the baracuda or surf PI.
I may be splitting hairs here, but I do get a variation of around 20 Hz "jumpiness" @ 1300 Hz (or PPS?) which is visible on the scope. The vertical traces twitche/stretch sideways.
Tried different 555's and decoupling caps. No change. Could it be the high ohm pots variability? I don't have to turn them much to get big changes in frequency/pulse width.

Step 5 Rx Preamp:
Here's a scope pic of my Rx out, that would be TP3 and reference curve is TP2.
Some things look funny to me. Is it normal?


Step 8 2nd Integrator:
Voltage swing is -3.4v to 4.1v, no problem I believe.I have to adjust it to -1.3v to get a quiet threshhold. Not sure if this is right.

Step 9 VCO:
Hmm, how should I express this. The frequency variation is very "compressed".
When getting target closer to the coil, the frequency jumps right up, then sticks at highest frequency the last 4 or so inches.
I was expecting a different sound experience - so maybe something is wrong here - or it is what it is.
Are there any sound files available as a comparison to other MPP's?

Hope I've not put too many questions here ...

Polymer

[waltr]

Here's a jfet data sheet that is made by mischievious ... errrr, data sheet makers - at least that's how I see it.
I found this one difficult to decipher at a glance, it's prone to misreading ... could have been done better.
[ATTACH]45660[/ATTACH]

That is not nice.

Thanks for asking waltr. The detector is working, but there are few things that I am not too sure about and have me doubting:

Step 3 Tx oscillator:
The frequency is relatively unstable compared to the baracuda or surf PI.
I may be splitting hairs here, but I do get a variation of around 20 Hz "jumpiness" @ 1300 Hz (or PPS?) which is visible on the scope. The vertical traces twitche/stretch sideways.
Tried different 555's and decoupling caps. No change. Could it be the high ohm pots variability? I don't have to turn them much to get big changes in frequency/pulse width.

Could be the pot is a little flaky. Try pulling the pot and measure what resistance it is set to. Then put a fixed resistor into the circuit.
If now a steady pulse rate the pot is bad.
Having a fixed resistor for pulse rate is fine. Or put in a fixed resistor a bit smaller then what you measure off the pot and add a smaller value pot in series.

Step 5 Rx Preamp:
Here's a scope pic of my Rx out, that would be TP3 and reference curve is TP2.
Some things look funny to me. Is it normal?
[ATTACH]45661[/ATTACH]

The slower rising edge on TP2 seems to be the MOSFET gate charge. the dip on the TP3 rising edge may be the slow gate signal plus the diode, D7.
The rising edge of the Coil drive (TX) is not too important. The falling edge (end of the TX pulse) is sharp and is the important edge.

The wiggles is simply Noise picked up by the coil and amplified by the pre-amp, Gain = 1156.
In your house will be noisier due to AC mains and the Integrator & SAT circuits will remove a lot of this.
Once you get outside and away from AC Mains noise this will be better.

Step 8 2nd Integrator:
Voltage swing is -3.4v to 4.1v, no problem I believe.I have to adjust it to -1.3v to get a quiet threshhold. Not sure if this is right.

Step 9 VCO:
Hmm, how should I express this. The frequency variation is very "compressed".
When getting target closer to the coil, the frequency jumps right up, then sticks at highest frequency the last 4 or so inches.
I was expecting a different sound experience - so maybe something is wrong here - or it is what it is.
Are there any sound files available as a comparison to other MPP's?

Hope I've not put too many questions here ...

Polymer

Not sure on the last two questions.
Hope George answers these.

[Polymer]

Hello waltr,

I would like to reply, but in continuation of the style with which you place your replies under the singular quotes. I like it.
How do you do this and what happens if I tick the "multiquote" next to the "reply with quote" button?
I cannot see a difference when activating it!?