InterCom / Door Phone

[Non89]

oic , i tot i only need to use 1 output .... ok , i will try it...

the polarity of both C4 capacitors having problem ?

 

[audioguru]

The original circuit and Boncuk's circuit have the polarity of both C4 capacitors backwards.
The emitter and collector of the transistor have positive voltages and the resistors to ground at the other ends of the capacitors is 0VDC.

 

[Non89]

ok , i will exchange the polarity of C4

 

[Boncuk]

The original circuit and Boncuk's circuit have the polarity of both C4 capacitors backwards.
The emitter and collector of the transistor have positive voltages and the resistors to ground at the other ends of the capacitors is 0VDC.

Did you consider the 180degree phase shift between C3 and C4?

 

[audioguru]

Did you consider the 180degree phase shift between C3 and C4?

Of course there is a 180 degrees phase shift in the signals. But it is AC and has no polarity.
The polarity of C4 is backwards to the DC.
I fixed my copy of the original schematic:

 

[Non89]

may i ask where can i find the BEL187 npn Transistor datasheet ( where is emitter, base and collector) , and what transistor can replace it ?

 

[audioguru]

may i ask where can i find the BEL187 npn Transistor datasheet ( where is emitter, base and collector) , and what transistor can replace it ?

Why are you asking about that very old transistor in this thread? The transistor was made in India by Bharat Electronics Ltd a few centuries ago. I can't dind a datasheet but I found its spec's on a list of old transistors.
Today I would use a 2N4401, 2N222A or BC337 and see its pins on its datasheet.

 

[Non89]

because i would like to try this circuit Transistor intercom circuit. - Electronic Circuits-Circuit Diagram-Electronics Projects-Design , if the preview intercom wasn't work ....

this circuit got "discordance" after i connected speaker , but the preview intercom show silent at all the time.....

 

[audioguru]

If you make the original circuit correctly then it will work perfectly. But you made only half of it so of course it didn't work.

The new circuit is simply a very old audio amplifier. It is bad because it has DC in the speaker and the transistors are biased wrong. A simple IC amplifier can replace it.
Two circuits make an intercom that will howl all the time because the sounds will go around and around.

The original circuit avoids howling feedback because it cancels your signal from your speaker.

When you said "discordance" do you mean that this intercom produced acousical feedback howling like I explained?

 

[4pyros]

I can't dind a datasheet

opps! Sorry I could not resist.

 

[DerStrom8]

opps! Sorry I could not resist.

Hahaha! There's more where THAT came from!

 

[Non89]

Of course there is a 180 degrees phase shift in the signals. But it is AC and has no polarity.
The polarity of C4 is backwards to the DC.


so i should connect it to AC?

 

[DerStrom8]

Of course there is a 180 degrees phase shift in the signals. But it is AC and has no polarity.
The polarity of C4 is backwards to the DC.


so i should connect it to AC?

Tell you what--You try that and let us know how it turns out

P.S. That was sarcastic

 

[4pyros]

so i should connect it to AC?

What AC are you going to hook it up to?

 

[Non89]

LOL...you are so evil... of course i nothing going to try it =.=

 

[Non89]

i was connected up both circuits by just using jumper wire and supply voltage on both circuits respecitvely......

the diagram show the voltage i meansure E,B,C,SPA,SPA respectively with Ground......

the output voltage from pin2 of potentiometer was extreamly low.... it just 0.0x - 0.5... i change both C3 & C4 polarity, but the result of pin2 output voltage is almost same... any idea ??

 

[Boncuk]

Hi Non89,

wrong again!

C3 connects to the collector of Q1 with it's positive terminal and C4 connects to the emitter of Q1 with it's positive terminal.

So only the polarity of C4 has to be corrected. (both boards)

I contacted the author of the circuit and he will remedy his design soon.

When googling for the design use the search words "full dulex intercom". You should find this page:

Full-duplex Intercom - RED - Page78

Boncuk

 

[Non89]

thank Boncuk~

by connecting both circuits with jumper wire and supply on both circuits respecitively.... the sound can transfer from "master mike" to "master speaker" , " slave mike" to slave speaker" ..... but the sound is very small..... how to amplify it ??

 

[Non89]

C3 connects to the collector of Q1 with it's positive terminal and C4 connects to the emitter of Q1 with it's positive terminal.

So only the polarity of C4 has to be corrected. (both boards)

yaya, i know .... i just trying both for testing XD

 

[Non89]

this is what i tested with changing C3 and C4 .... both connected +12V DC supply respectively....

C3 and C4 positive polarity connected to Q1 , jumper wire was connected between both circuits Q1 Collector : Speak in mike 1 or mike 2 = Both Speaker voiced out

C3 positive polarity connected to Q1 , C4 negative polarity connected to Q1, jumper wire was connected between both circuits Q1 Collector : Speak in mike 1 or mike 2 = Both Speaker Voiced Out

C3 and C4 negative polarity connected to Q1 , jumper wire was connected between both circuits Q1 Collector : Speak in mike 1 or mike 2 = Both Speaker voiced out

(all the voiced out from Speaker 2 was not clearly....)



now i pull out the jumper wire and changing the C3 and C4 as 3 solution above, and you can guess the result as shown : Speak in mike 1 = Speaker 1 voiced out, Speak in mike 2 = speaker 2 voiced out(but very quietly....maybe i will change the R10 and R11 value or instead with potentiometer)