Step 5 says:
"Place a cola can close to the coil, and the voltage should drop
by a few 100s of millivolts. A coin will only drop the voltage by a few 10s of millivolts."
What is the vertical scale on the O'scope?
I am guessing 1V/div. Then the Voltage drop with a coke can is about 100mV.
This is a less than Step 5 indicates and may be due to the lower coil inductance.
Otherwise it looks like Step 5 is working.
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MPP revE need help
I my name is Alban I am 28 years old I am from France and I like diy projects.
I wanted to start an electoniqual project and i chose to try to build a metal detector so i find this forum and i choose to build the MPP rev-E for the good builds instructions and the support on this forum.
I buy all the parts and an old oscilloscope for 50? and let's start the project.
The three first step was ok !!
For the fourth i choose to replace R4 by a 1k ohm potentiometer to provide adaptable damping resistor if i wanted to adapt new coils on my future MMP E.
I build a coil with 17 strand of 1mm outer diameter copper wire. i used a loop diameter of 25cm and I find a 250mH inductance on this site https://www.allaboutcircuits.com/too...ce-calculator/
-1st theat : did this coil can fit with this detector because of is low inductance ? or i need to build a new one with thinner wire ?
-2nd threat : i tried to adapt the damping resistor but i don't understand the signal that i read on tx pin... i see the diferences on the signal when i moving the damping resistance but i' m not sure to see the critical damping value. I puted the resistor to 300ohm that seem to be the point of change on signal reaction and i chosed to continue.
Now i'am on the fifth step and when i put a cola can on the coil i just see a very little movement on tp3. Is my osciloscope signal is normal ? Do I need to change something to get a better signal reaction when i put a cola can on the coil ?
I hope you will help me to improve my knowledge on how i could build this metal detector.
Thank you for helping !!
Best
Alban
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