Surf Pi modifications (clarification needed)

[kt315]

@kt315: I don't know what you want... YES i know, the symbol you marked is a piezo!

A piezo speaker has high impedance (high resistance), some headphones have low resistance. WHAT and WHY will low impedance headphones alter the function of the detector?

[6666]

so you only need two wires for the speaker ?

[ionut_mtb]

this is nonsense...
this one better!

[ionut_mtb]

But I'm more interested why a low impedence speaker would not work in the surf pi circuit.
cheers

I can't give you the answer to this question, but i can tell you that i use low impedance headphones with my homemade surf pi, without problems. No modification to the schematic. This will be the last problem in your project.

[6666]

this is nonsense...
this one better!

[ATTACH]41153[/ATTACH]

So you are useing earth return for speaker connection ?

Oh the silly season is here

[Qiaozhi]

Why would change the resistance of the speaker change the behavior of the detector? On both the Surf Pi and Minipuls Plus...

The impedance of the speaker would only change the volume, wouldn't it? Maybe when the resistance of the headphone is so small, it would destroy the audio switching transistor (or am i totaly wrong?)

Changing the speaker wll not affect the way the detector works, but the audio volume may just be a bit lower. As dbanner said, if you're at the beach then you will need to use headphones.

[dbanner]

[dbanner]

[kosacid]

for sound no mod is needed im using iClever Universal Bluetooth Stereo Transmitter IC-BTT01
and a set of 4.0 Bluetooth head set, i can hear objects a few feet away and zero in on them it was just by chance i found out it works that way, but i can hear small changes in the field, unlike when you uses just standard head phones on just the buzzer, its because of the transmitter acting as a preamp

[ulix]

@Qiazhi: Thanks for clearing this up! So I understood the schematic... (Did mention that the audio volume would be lower in post #6) but this can be changed in the schematic/circuit.

Thanks as well to ionut_mtb and kosacid for clarifying.

[kt315]

is Ohm's Law so hard for understanding? i learn it in 8th class of school. 15 years old. PHYSICS lessons.
one time and on whole life. low impedance of speaker - 8 ohm? 12 v power suply (minus) 2 v approx COLLECTOR-EMITTER we get 10v.
ok. 10 volts on 8 ohm (transitor of end stage is working in key mode - learn electronics).

so 10 devide on 8 we get OP LA LA 1.25 ampere. CAN THE TRANSISTOR in TO-92 work on 1.25A?
put your fingers in the socket.

[ulix]

Hi kt315,

no ohm's law is pretty easy. But you should read and follow the current flow correctly. Watch the whole circuit and not only small areas.
Don't forget that the circuit consits of R18 with 150Ohms as well! Then it's more likely to be 10V/158Ohms which equals to 0.064A.
The Datasheet of the MPSA13 (Onsemi) rates an Maximum Collector Current (-Continuous) of 500mA.
SO if I'm not totaly wrong: 0.064A<500mA, which should be fine.

You did as well neglect the resistor R13, which can range from 0Ohm to 1kOhm.
- So the speaker (with 8Ohm) in parallel to a 0Ohm Potentimeter is? => 0Ohm (*)
- Speaker parallel to a Potentimeter with 1kOhm? => 8Ohm
If we now neglect the reistor of the speaker parralel to R13 (short, marked as *) we have 10V(which should be more like 12V-1.5V) and get a current: 10V/150Ohm=0.066A.

[bklein]

Why do you wish to use low impedance headphones vs higher impedance ones?
My Koss Pro4AA’s are pretty low impedance and stop the CTX WM10 from working. I have read several cases where low (how low?) impedance phones have damaged detector output circuits. If you go a low impedance audio route with added amplifier you increase battery drain and likelyhood of noise into detection circuits. Put an amp in the headset or inline. Try earbuds.

[kt315]

ulix
R18 used for the dummies they do not burn the circuit by low impedance headset?
a protection from fools?

[ulix]

Hi bklein,

my thoughts were more about keeping the detector as versatile as possible. So accepting a wide range of headphones... (typical headphones/ earbuds are arround 25Ohms, in comparision to 600Ohms, it's low)

I read here as well, that a lot of detectors "stop" working when some headphones are connected. But I think it's not the detector which stops working more having no sound. I could be wrong... but exactly this statements caused my question.
I wanted to understand the fundamentals behind it...

@kt315: like me... :-D