GC-101H

[ivconic]

"...Powering this metal detector is a typical 9v battery.
The device draws:

* 5mA when turned on,
* 70mA during an alert in vibration mode, and
* 33mA during an alert in audio mode.

Depending on the frequency of alerts and battery chemistry, an on-time of up to 240 hours can be achieved.
To provide a more stable voltage to the electronics, a 5v linear regulator is used. This device uses a 7805 voltage regulator in an SOT-223 package.
To alert the presence of metal a buzzer can be used. This buzzer has the part number TMB12A05 printed on it. This buzzer emits a 2300Hz tone at 85db. This buzzer is powered by 5v and can draw up to 30mA...."

[ivconic]

Scanned:

[ivconic]

Schematic:

[ivconic]

PCB:

[ivconic]

Details:

[ivconic]

Coil = 1mH

[ivconic]

[bernte_one]

Good Morning Ivica,

do you think it could be used for freshwater diving?

[ivconic]

Good Morning Ivica,

do you think it could be used for freshwater diving?

Probably yes. If sealed and waterproof.
But i am rather interested to make pinpointer from it.
I will keep original device as it is and draw another smaller pcb for pinpointer.
I already tested original device with much smaller coil and it is working just fine.
It is simple, straightforward and works very stable. 5-6cm distance on single coin is just alright for pinpointer.

[ivconic]

Once i assembled it again; i had to test it to make sure i did it right:

[ivconic]

[ivconic]

And most interesting and funny part was to hook up completely inadequate 1mH choke to act as "coil"!

[ivconic]

"...To provide a more stable voltage to the electronics, a 5v linear regulator is used. This device uses a 7805 voltage regulator in an SOT-223 package..."

This is nonsense.
It is obvious on schematic that 7805 serves there for almost nothing!
It is used there only to "sense" voltage drop and lit the led diode.
Perfectly stupid way to waste one 7805!
That whole part can be omitted to preserve space and make smaller pcb.

[perdica 2]

there are actualy two LDO's, small corectiion to your's schematic