Just Finished mini pulse plus lacking distance whats wrong

Control pots seem to work it can detect a shoe polish tin but only about 8 inches away a dime size coin almost has to be touching the coil to sound off not getting the sensitivity i have heard about and definately not getting the distance any help as i don't know where the fault is lies could it be a chip at fault or something else Any help on the possible cause would be appreciated Graham

[surfdetector]

Control pots seem to work it can detect a shoe polish tin but only about 8 inches away a dime size coin almost has to be touching the coil to sound off not getting the sensitivity i have heard about and definately not getting the distance any help as i don't know where the fault is lies could it be a chip at fault or something else Any help on the possible cause would be appreciated Graham

It would be helpful if you posted some pictures. For instance the output of the pre-amp compared to the main sample pulse. That way we can help you better.

[Graham]

Got some screen shots captured of my laptop via usb oscilloscope hope this helps Graham





Seems like its not amplified or pre amped enough if i new what part was faulty i would try replace it Graham

[Emersonpaz]

It may be an operational amplifier that is not of good quality.
works however with limitation

[Graham]

Just what parts or parts would the operational amplifier be out of the mini pulse plus rev e parts list may be able to replace them if they are available in Australia thing is i don't know which parts are the operational amplifiers thanks for the help hope i can figure out which parts may need changing. Graham

[waltr]

Just what parts or parts would the operational amplifier be out of the mini pulse plus rev e parts list may be able to replace them if they are available in Australia thing is i don't know which parts are the operational amplifiers thanks for the help hope i can figure out which parts may need changing. Graham

Google search each part used then open and read the Data Sheet.
This will tell you if its an op-amp and much more.
Good exercise to learn more about the circuit.

[Graham]

Found op amps TL071CP and TL072CP both seem to be available here in Australia thinking of replacing both as i don't know how to test them and hope this fixes my MPP detector sensitivity lack of distance problem as i can't really use it the way it is not able to pick up small items at any worthwhile distance again thankyou for you help crossing fingers . Graham

[surfdetector]

Found op amps TL071CP and TL072CP both seem to be available here in Australia thinking of replacing both as i don't know how to test them and hope this fixes my MPP detector sensitivity lack of distance problem as i can't really use it the way it is not able to pick up small items at any worthwhile distance again thankyou for you help crossing fingers . Graham

Take a picture of TP3 versus TP6 and post it.

That is the pre-amp output and the main sample pulse.

What are your coil specifications and what are you using for a damping resistor?

[Graham]

Already posted some screen shots of step 5 TP3 and step and step 6 TP2 and TP6 which is in green ,damping resistor used is a jig with multi turn10K in series with 200R and 2K opposite forgeot the specs of my coil but will check on the weekend .while here i was looking for an alternative for the IF412A used in the Baracuda Detector one web site says look at LT1057 pit compatible but will this work as i think i have one spare the original is hard to find and expensive online. Graham

[surfdetector]

Already posted some screen shots of step 5 TP3 and step and step 6 TP2 and TP6 which is in green ,damping resistor used is a jig with multi turn10K in series with 200R and 2K opposite forgeot the specs of my coil but will check on the weekend .while here i was looking for an alternative for the IF412A used in the Baracuda Detector one web site says look at LT1057 pit compatible but will this work as i think i have one spare the original is hard to find and expensive online. Graham

It would be helpful to see a single screen shot of TP3 and TP6 rather than having to toggle between your previously posted separate shots.

That said, it looks like you have quite a bit of ringing going on, your damping resistor is not correct.

[Graham]

TP3 Screen Shot
TP6 Screen Shot
using 470 ohm setting on Damping resister Jig
Coil Specs 4.50 ohms and .43mH about 22.5cm diameter
Step 1 (-5.03 V) Step 2 (4.94 V)
Step 6 at TP9 and TP10 showing about 17us not 10us as noted in step.
Still not getting any worthwhile response working but not anywhere good enough. Graham

[Graham]

Found a mistake that probably is giving me problems with mini pulse plus rev e. I have put some capacitors in the wrong place mixed up C8 and C13 .
I must have mixed up these parts from accidentally looking at the Baracuda metal detector instructions instead of the MPP Detector instructions tomorow i will try and swap these hope this fixes my sensitivity issue getting distance. Graham

[surfdetector]

What did your flyback look like on Step #4?

The pre-amp signal does not look correct TP3

[Graham]

You were right the pre-amp wasn't correct after carefully looking in this area found an incorrect capacitor in C8 replace for correct 1uF, then i found missing small capacitor C13 220pF purchased and fitted then re adjusted settings now working approx 8 to 10 inches on different coins thank you for all your help now i just have to work out a coil cover and control box for pcb and pots. Graham

[surfdetector]

You were right the pre-amp wasn't correct after carefully looking in this area found an incorrect capacitor in C8 replace for correct 1uF, then i found missing small capacitor C13 220pF purchased and fitted then re adjusted settings now working approx 8 to 10 inches on different coins thank you for all your help now i just have to work out a coil cover and control box for pcb and pots. Graham

Glad to help you resolve the matter. Happy Hunting