PICKINI - an easy to build PI detector

[Waikiki_Sweep]

What a problem to add LM368 or TDA2822 amplifier to get it as loud as you want?
I am using TDA2822M for last few years inside my Surf PI. It helps me get it loud and significantly increase stability of metal detector because
amplifier has its own +5V power line with additional 78L05 so no more spikes of current in speaker goes into detector power supply. It works much smoother than original Surf PI.
Also I am mixing detector sound with MP3 stereo music player output having a lot more fun running with my machine in water.
So I vote for amplifier IC!

[satdaveuk]

Here is the 3 transistor as promised its amplification is 15x determined by R1 R3 and P1
Input sense 95MV Draws 25MA when idle and a total consumption of 180MA working flat out at 9v
Distortion .1%
If you want more base just increase electrolytic capacitor on main output to 1000MFD.
Used this design many times over the years for different projects and works well.
Output power using spec on diagram is around 250MW same as a typical small radio.
Impedance 4-8 ohms, Should be OK with 32ohm headphones .
Over the weekend will put one together and check it out with the Barracuda and the Minipulse3 which works with pulsed clicks and give you results.
Although its designed round 9V supply in my way of thinking it should handle 12v direct from battery.
The second circuit I never got round to building but thinking positive as most of us here do, it maybe just the ticket based round one single Darlington type transistor which is the MPSW45A and gives a whooping 1Watt output
They are no longer manufactured and when you can get them a bit pricey so over the weekend if its raining shall put that together also but try and get away with either MPSA14 or BC517 which are both Darlington type.
Could use a standard NPN transistor but the gain would be shot to pieces so that's a no go.
If that does the job which again feeling postive then due to component count could be mounted anywhere even made ultra portable to use on any detector where required even thinking of a jack plug to socket in a very small encapsulation.
Will let you all know soon
Regards

[bernte_one]

and this ? low supply voltage
http://www.radanpro.com/Radan2400/Pojacala/stereo.gif

[nick holas]

hi all
i just finish to solder my pickini mod board and when i switch on i hear 3 tone than when i connect my coil there a little spark on the plug and it short circuit,when i disconnect, i hear 3 tone again
some one got and idea ?

i join my pickini mod board(only little smaller than the F117 original board ,no other modification)

[F117]

There has to be a short circuit between the 12V output and GND when you connect the coil.
Switch off the power, connect the coil and measure with an ohm meter between the 12V and GND.

OR

you are connecting the coil between the COIL and SHIELD points on your layout - it should be between the 2 COIL connection points.
OR
the connection is right, but you have a short between one of the coil connection wires and the coil shield. You should have 3 wires:
the 2 coil ends and a shield wire. When you measure ohms between the 2 coil wires, you should have something close to nothing ( 2 - 5 Ohms ).
Between shield and either one of the coil connection wires should be infinite ohms (open).

This is the original layout:

[Waikiki_Sweep]

and this ? low supply voltage
http://www.radanpro.com/Radan2400/Pojacala/stereo.gif

TDA7050 is awesome because no external parts are required. But it is too rare. Hard to find. Also it has 8-SOIC case. That one with 8-DIP case TDA7050N even much harder to find.
TDA2822,TDA2822M needs two additional capacitors in comparison with TDA7050 but it is very cheap and you can find it everywhere easily.
Supply voltage: TDA2822 - 1.8V - 12V. TDA2822M - 1.8V - 15V.

[satdaveuk]

TDA7050 is awesome because no external parts are required. But it is too rare. Hard to find. Also it has 8-SOIC case. That one with 8-DIP case TDA7050N even much harder to find.
TDA2822,TDA2822M needs two additional capacitors in comparison with TDA7050 but it is very cheap and you can find it everywhere easily.
Supply voltage: TDA2822 - 1.8V - 12V. TDA2822M - 1.8V - 15V.

Thanks for that, just ordered 4 of the TDA2822M from Farnells which can be used dual or bridge mode, cost 88p each incl vat and p/p , Also bought another 4 off TIP127 for 42p each fully inclusive.
Still going to have a bash at the darlington single transistor audio output because its got no hidden AGC etc and of course a big problem with these all in ICs typical LM386 is the auto mute which is something that we dont want , typical symtom is when a target is detected with strong signal the output will almost disappear.

Regards

[Waikiki_Sweep]

I have tried to find more info about AGC but looks like many of power amplifiers (including LM386) have no AGC feature as it is absent in their datasheets.

For example:
If you need AGC you can add it with few external components to TDA7052A If you do not need AGC you can use TDA7052A as is - with DC volume control.

Why output disappears?

I think if you will use capacitive coupling for LM386 input signal and large enough capacitor to connect speaker there will be no problem with strong signals.
Also may be it drains to much current for strong signals so power supply go low and output disappears. Or LM386 was bad or some capacitors were fried.
It is just my guess.
Also people blaming on LM386 that it easy go into oscillation. If it starts oscillating on higher, non audible frequency you will see that output disappearance.

Also if someone need TDA2822M. Five TDA2822M on eBay I saw for $2 with free shipping.

[satdaveuk]

Hi
Maybe I should do more experiments with the LM386 after taking note of your comments because I have loads of those in stock.
I know you can buy cheaper on ebay but normally its last resort for me to buy on there due to fact you dont really know what your buying.
I prefer branded components from reputable manufactures, Good instance is the TIP127 from china , cheap but crap.
Bought cheap 3.5mm jack sockets, they were badly engineered ill fitting nuts , got what I paid for.
Regards

[Waikiki_Sweep]

Yes. You are right. Quality is a problem. Buying anything from China is risky. I got a crap numerous times. But buying from Radioshack same China crap for 10 X price looks ridiculous too.
50% of components I am buying from Digikey hoping to get quality items but it is expensive because you can get reasonable price only for wholesale 100 or 1000 items. Also shipping costs a lot.

Parts from China 10 X cheaper and shipping is free but slow. But often they works good and it lets to save a lot.

Here in US you can go into any supermarket like Walmart and find that everything made in China. And sure nothing works properly.
Also, as you know most of worlds electronic devices assembled in China.
How do you know what parts they used for your digital camera or phone - black or branded?. I suspect same parts they selling on eBay too.

Last example. Buying 1000 resistors different values will costs $100 on Digikey.
Or I can buy a set 1% metalfilm resistors from China for $3-5. I have checked them with multimeter and they are correct. Why not to save.

[nick holas]

Hi allthanks f117 your right i ve made wrong connection between coil shield and coil but now i ve got a continuous beep playing with lm318 pot ( pin 3 at 8v) and sens pot (minimum) nothing works, only when i put less than 7 to 6 v to pin 3 of lm318 the beep stop, don t know what to do else

[satdaveuk]

Hi
Made the TDA2822M PCB universal so you can populate board either stereo or mono in bridge mode, Have posted circuit and bottom mirror of PCB, can you check it for errors please.

Regards

[Waikiki_Sweep]

Hi
Made the TDA2822M PCB universal so you can populate board either stereo or mono in bridge mode, Have posted circuit and bottom mirror of PCB, can you check it for errors please.

Regards

Good job!

VR1 and VR2 have to be connected with 3 wires not 2.
Also I think 10K is better value for them because with lower input impedance you will hear less noise and interference.

I can advice also to add 7805 voltage regulator to power it with +5V. It will help to stop any interference from amplifier to metal detector power supply.
Or you can use 1000 x 16V capacitor and 20 Ohm resistor to keep 12V power but insulate amplifier power supply from metal detector 12V power supply.

Also picture with components placement will help to assemble circuit right.

Thank you.

[sinclairuser]

if you want non obsolete(current) chips in quantity, open an account with st and ti,and microchip they are more than happy to sell you 20,50,100 or more, i didn't do this till recently as import tax and customs were a worry, but in quantities under 250 units its not a problem, i joined them and got samples, then contacted them directly about quantities of 50-100,and no problem proper stuff with no lemons.
import tax and so on applies to the likes of cscope as an example who may order 1000's or more at a time, try it its better than risking fakes or duds, china suppliers are ok for resistors and not much else.
p.s. also the big companies give you freebies, i enquired about a certain chip,and they did not have dip versions in stock, so bought soic units as i needed them, when they arrived ti had put dip adaptors in for free, and samples of a newer dip alternative to try you wont find that kind of service on ebay!.

[satdaveuk]

Good job!

VR1 and VR2 have to be connected with 3 wires not 2.
Also I think 10K is better value for them because with lower input impedance you will hear less noise and interference.

I can advice also to add 7805 voltage regulator to power it with +5V. It will help to stop any interference from amplifier to metal detector power supply.
Or you can use 1000 x 16V capacitor and 20 Ohm resistor to keep 12V power but insulate amplifier power supply from metal detector 12V power supply.

Also picture with components placement will help to assemble circuit right.

Thank you.

Thanks for your time
your right in most cases about using 10k pot , but was just trying to make it universal as possible because no one got back to me on output/impedance of this particular detector. In most cases where a detector already has a volume control, A pair of fixed 10k resistors will do the job hence why there are only 2 connections on the PCB which I intended to point out but totally forgot about.
Power up wise its up to the individual how they want to source it, some may want to supply independently by just plugging a battery to it so they can use on various detectors , type of plug and play in a separate independent housing.
If supply is integrated to detector then a regulator wired direct to main source of supply is advised, and as you stated the 7805 is a good candidate although there are others out there that will do the job nicely .
I have not built this yet so cannot give opinion but going by your results and looking at manufactures spec of the chip it should fit the bill nicely ticking over at 5-7 milliamp 1+1 watts = 2 watts,1.4-14v supply, cannot get much universal than that.
I tried the MPSA14 Single transistor Idea on breadboard and was disappointing because firstly to get any usable output into 8-16ohm speakers it was drawing way to much currant , needed speaker impedance in excess of 100ohms which is not off the shelf, and further looking into the spec of the transistor its very different to the MPSW45 so was pushing the boat out anyway Have Shelved the Idea for the time been due to cost and availability of correct part .

Regards