Metal detector with meter discriminating

[Qiaozhi]

Hello,
Sasho.
I am trying to make this PCB,but its look like pin configuration on IC CA3140 is reverced!!+and-????
Am I right?
Please explain!
Thanks

Why do you think the inverting and noninverting inputs are reversed?
Looks ok to me.

[Sasho-bg]

To Qiaozhi
No.Schematik is correct.

[Geto]

NOT To Qiaozhi SASHO!

I post this question!NOT Qiaozhi
I am now trying to make PCB for this schematic of yours and found that:

[Geto]

to Sasho-bg

I see that in the circuit that you give the + and - are reverced!!
Is this because I am begginer,and cant read between the lines?Or there is mistake?
Thanks

p.s.can I use 50-0-50 ma meter for this scematic?

[Qiaozhi]

I see that in the circuit that you give the + and - are reverced!!
Is this because I am begginer,and cant read between the lines?Or there is mistake?
Thanks

p.s.can I use 50-0-50 ma meter for this scematic?

Hi Geto,

Some people will draw an opamp with the - (inverting) terminal at the top and the + (noniverting) terminal at the bottom. Others like it the other way around. You just need to be careful when you build the design, and note the correct connections. This can often lead to mistakes, especially when the two are mixed together in the same schematic, which is not good practice.
In other words, just make certain that you connect the inverting terminal to pin 2 and the noninverting to pin3. Essentially it makes no difference which method you use.
It looks like this detector requires a 50-0-50 uA meter, but Sasho should be able to confirm this.

[Geto]

To Qiaozhi

Hello,
Thanks for help man!
I will ask For your help again I am shore for that.But I have to make this PCB!
In which Country you are located?

[Geto]

To Qiaozhi

What leads you on that I can use 50-0-50 ma meter?
Because I wanna this project to be as close as I can reach!

[sasho-bg]

METER IS -50-0+50 MIKROAMPERS!!!

[Geto]

Hello,

Thanks!
What is this pn4393?
Can I use some equal substitue?Any Ideas?

[porkluvr]

2N4393 substitute

Hello Geto
One of the main features of 2N4393 FET is low cut-off voltage. I have read other people suggest that a European equivalent is a BF245c, although from looking at the spec sheet, I can't see why BF245A is not a better choice from that group. Maybe somebody can clarify that.


TIS75 should also work. I think also J113 should be OK, but it has exactly reversed pinout. Just turn J113 around 180 degrees.

Hmmm, does anybody wanna thwack me for my choice of BF245A (or any of the others)? I could be a bonehead.

[kt315]

porkluvr,
what is your opinion about 2N7000 (2N7002)? I see these used on motherboards.

[Qiaozhi]

What leads you on that I can use 50-0-50 ma meter?
Because I wanna this project to be as close as I can reach!

Hmmm... I don't think I said a 50-0-50 mA meter is ok. I said that it looks like it needs a 50-0-50 uA.
Anyway, I see that Sasho has already replied.

[porkluvr]

porkluvr,
what is your opinion about 2N7000 (2N7002)? I see these used on motherboards.

Kt315:
The 2N7002 is enhancement mode MOSFET. So, I thought it appropriate, and a simple matter to test with pull-up to positive rail instead of pull-up to ground.

I hooked up LTspice to test the idea. I did not "wire" the exact same circuit, just a quick and dirty test with a 200mvP-P 50kHz sine wave getting switched through; something for easy to eyeball results. Tested side-by side with TIS75 and 2N4393 (remember these are only models, and not the real thing).

I was disapppointed. I tried several different pull-up biasing schemes; different voltages (including ground), and different pull-up resistor, but the 2N4393 and TIS75 performed (their circuits remained unchanged) while the 2N7002 did not perform well at all, no matter what I tried. Of course, I did not try everything, and maybe I'll try again later, but enough is enough. I know when I've been beaten. We have something that works, so there is no need to fit a square peg into round hole (not today)!
Dang it, I've got a bucket load of these in the SOT23 package that I hope are good for something besides driving LEDs and buzzers. If I come up with a better use for them I'll let you know!
Consider that 2N7002 is more of a power device, whereas 2N4393 is for small signal. I can't explain any better than that, it's all I know.

[porkluvr]

substitute pinout

Hold on - 2N4393 and J113 have the same pinout, and it is the TIS75 that must be turned 180 deg. Aggh. I'm sorry, but I lied.

Oracle I ain't. Dyslexic, oot. Always be safe and consult the appropriate manufacturer's spec sheet for any device before applying overvoltage.

[Sasho-bg]

Work also with КП303.Made in Rusia.