MPP beach rev-e problem

[Hrthomas]

Hi
I have finished my rev-e build, but when testing it I get a constant high sound from speaker, and when i put a item over my coil it dissapears, so for me it looks like the signal is reversed or something?
On step 7 the voltage drops when i put something over the coil.. I have meassured my coil, and it is 409uh (mono coil)
all the other meassurement looks ok..

[Qiaozhi]

Hi
I have finished my rev-e build, but when testing it I get a constant high sound from speaker, and when i put a item over my coil it dissapears, so for me it looks like the signal is reversed or something?
On step 7 the voltage drops when i put something over the coil.. I have meassured my coil, and it is 409uh (mono coil)
all the other meassurement looks ok..

Did you read the part in the Build Document where its says:

As stated in previous revisions, if you go through the following steps carefully, and in order, you
will have a greater chance of ending up with a detector that actually works. Please do not proceed to
the next step until you have solved any problems encountered in the current step. If you get stuck at
any stage during the build, then seek help in the Geotech forums before moving on. Do not simply
populate the whole board; discover it doesn't work (which will be the most likely result) and then
post in the forums: "I've built the Minipulse Plus, and it's not working. What's wrong?” .... as you
will receive little sympathy from other Geotech members. You have been warned!

I'm asking this question because you shouldn't have been able to get past Step 7 (without seeking help) if the voltage did not increase when a metal target was placed near the coil.
Also, do you have access to an oscilloscope?

[Hrthomas]

I did the step by step, but in step 7 i did not noticed the voltage drop, i just noticed a change in voltage and moved on. Yes i have an oscilloscope..

[Qiaozhi]

I did the step by step, but in step 7 i did not noticed the voltage drop, i just noticed a change in voltage and moved on. Yes i have an oscilloscope..

That's good.
Can you post an image of the pre-amp output at TP3?

[Hrthomas]

[anil.berk]

Hi, I am also struggling with the same issue. I could not solve the problem on step 7.

[Qiaozhi]

Hi, I am also struggling with the same issue. I could not solve the problem on step 7.

Is there no change in the signal?
Can you post a scope image?

[anil.berk]

Is there no change in the signal?
Can you post a scope image?

Thanks for your reply Qiaozhi. I just solved the problem

[surfdetector]

Thanks for your reply Qiaozhi. I just solved the problem

In order to help others, how did you solve the problem?

[anil.berk]

In order to help others, how did you solve the problem?

I shifted the main sample pulse much more right because it was not able to sample the difference.

[convola]

I shifted the main sample pulse much more right because it was not able to sample the difference.

How did you shifted main sample pulse more right? In my circuit TP6 like this picture

[Altra]

Looking at your photo. It appears your Tx pulse is approx 400us based on your scope setting of 250us/div, This is not correct, it should be around 100us or less, Check all the capacitors and resistors around the NE555 timer U1. Maybe you used a 470n when it should be a 47n? I think if you fix the tx pulse your other problem with the first sample will be solved

[convola]

Looking at your photo. It appears your Tx pulse is approx 400us based on your scope setting of 250us/div, This is not correct, it should be around 100us or less, Check all the capacitors and resistors around the NE555 timer U1. Maybe you used a 470n when it should be a 47n? I think if you fix the tx pulse your other problem with the first sample will be solved

tp3 and tp2 like this. it is 100us pulse and 1ms period.

[convola]

tp3 and tp2

[Qiaozhi]

I think you may be confused about the sample timing.
TP6 is the sample delay, and TP9 is the main sample.