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Needing 6 pinpointers last year 1 each for the grandchildren making 8 looked to be quite an outlay looking through the archives I came across the mini-max which seemed to have a simple coil and would be easy to set up looking in my parts I used the following.
Q1 Q2 bc109 bcy72 ?
U1 CA3240
Q3 bc109
diodes IN4001
BAV99 replaced by single IN4001
Power a 9V battery with a 5Vreg in place of Q4 bt1
L2 C4 replaced by electo cap 10uF
C1 C2 C3 were kept as 100V working.
Put together on 2 pieces of veroboard with osc and components upto C7 on one board close to coil.
A few changes around the threshold pot to set correct voltage level (I forget what they were)
Every one worked first time (after first) and been used many times by 3 to 10 year old's the best test ever designed to find any weakness lol.
No photos or instructions as they were made up from what I had.
Now a few questions what is U1A doing?
Would it be possible to add a coil? around 500mH changing caps 1 2 3 as I have now to make 6 detectors and several underwater (snorkelling) detectors.
In a quick test at a dig it had the same or a little more depth than a garrett probe! the first one on bench at one point was detecting at 6",
suspect there was some feedback?? as I could not get it to repeat with scope turned on!!!
Q1 Q2 bc109 bcy72 ?
U1 CA3240
Q3 bc109
diodes IN4001
BAV99 replaced by single IN4001
Power a 9V battery with a 5Vreg in place of Q4 bt1
L2 C4 replaced by electo cap 10uF
C1 C2 C3 were kept as 100V working.
Put together on 2 pieces of veroboard with osc and components upto C7 on one board close to coil.
A few changes around the threshold pot to set correct voltage level (I forget what they were)
Every one worked first time (after first) and been used many times by 3 to 10 year old's the best test ever designed to find any weakness lol.
No photos or instructions as they were made up from what I had.
Now a few questions what is U1A doing?
Would it be possible to add a coil? around 500mH changing caps 1 2 3 as I have now to make 6 detectors and several underwater (snorkelling) detectors.
In a quick test at a dig it had the same or a little more depth than a garrett probe! the first one on bench at one point was detecting at 6",
suspect there was some feedback?? as I could not get it to repeat with scope turned on!!!