Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

is this walkie talkie circuit correct

Status
Not open for further replies.
A

anny999

Junior Member level 1
Joined
Aug 10, 2014
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
135
i have seen many circiuts for walkie talkie. is the circuit i have selected and attached below correct? should i go for it?
because i dont have time for trying and testing...it is just a mini project of mine. it need not be of very high range
walkie talkie circuit.png

i have taken this circuit from here

homemadecircuitsandschematics.blogspot.in/2014/06/simple-walkie-talkie-circuit.html

i have only got 2 days to build it..so plz help
 

chuckey said:
Can you get hold of the correct transformer?
Frank
Click to expand...

umm..no. how do get to know what transformer is to be used?

are there more things like that that need attention?

if this circuit can't be made then can someone suggest a better one?
 

All simple circuits like that are a compromise. If you want frequency stability, sensitivity and good audio quality you need to look at using different transmitter and receiver circuits rather than combining them to use fewest parts. A good design will be considerably more complicated!

The transformer you need is an 'audio output transformer'. They were once common before IC amplifiers took over. If you can find an old (older the better) transistor radio there is a good chance you can salvage one from it. It will be a rectangular metal box with a plastic bobin inside it, usually wrapped in plastic tape. They have 5 wires leaving them, two will connect to the loudspeaker as in your schematic. The side with three wires can be used end to end, ignoring the middle wire or from the middle wire to one end. If you use middle and one end, it doesn't matter which end you use but do not connect the two ends together.

Brian.
 
thank you brian :) but how can i come to know what voltage and current rating transformer i should use for this circuit?
 

It's a small audio output transformer so it would not have a voltage or current rating. If it has a rating at all it would be somewhere in the 150mW to 500mW range. It matches a transistor amplifer output stage to a low impedance loudspeaker. Typically they would fit inside a 20mm cube so they are quite small.

They look like this: https://www.maplin.co.uk/p/miniature-audio-matching-transformer-200mw-lb14q

Brian.
 
you are right, it does not have a voltage or current rating. i bought an audio transformer which looks like this

WP_20141104_004[1].jpg

it has only two wire as it can be seen..

betwixt said:
The transformer you need is an 'audio output transformer'. They were once common before IC amplifiers took over. If you can find an old (older the better) transistor radio there is a good chance you can salvage one from it. It will be a rectangular metal box with a plastic bobin inside it, usually wrapped in plastic tape. They have 5 wires leaving them, two will connect to the loudspeaker as in your schematic. The side with three wires can be used end to end, ignoring the middle wire or from the middle wire to one end. If you use middle and one end, it doesn't matter which end you use but do not connect the two ends together.

Brian.
Click to expand...

will it work? how to connect it?
 

That thing you have bought looks like a choke and not a transformer. A choke has one winding, some times with a centre tap, so they have 2 or 3 wires or pins. Transformers have at least two windings , so at least 4 wire/pins, or as Betwixt said, one winding may have a centre tap, making 5 pins/wire in all.
Frank
 
i actually cant get hold of an audio transformer anywhere at my place. not even online.
is there anything else that can be used in place of audio transformer?

i found this site which teaches to make one's own audio transformer
**broken link removed**

should i make one or there is another option?
 

To make one you need the core and that would be even harder to find than a transformer!

What country are you in? Someone might be able to help you find a local distributor.

Brian.
 

i am from india. it is not available nearby...
can i use a step down transformer in its place? or should it be step up?
 

The transformer and three audio transistors that drive it can be replaced by a modern power amplifier IC like an LM386 for receiving, and an electret mic with an opamp for its preamp can be used for transmitting.

It looks like the receiver is a very simple Super Regenerative Receiver type (look in Google) and the crystal is not used for receiving. If it is sensitive enough it will pickup many 27MHz transmissions at many frequencies at the same time.
 
i have found these audio transformers...are they correct? which one should i use?
WP_20141108_004.jpg
the one with blue center has 4 wires on one side and 2 on the back side. the black coloured one has got 5 pins.
i dont have any specifications about any of these...

- - - Updated - - -

how do i come to know how many watts speaker do i have to use? 8 ohm but how many watts?
 

may be you should compare this circuit with a few others to decide if it is correct
or not
 

hey, can anyone explain the function of each component like the transistor configuration, their connection with resistors over here? and how to decide the value of the capacitors and resistors in any circuit like this?
 

CatLikeBread0 said:
hey, can anyone explain the function of each component like the transistor configuration, their connection with resistors over here? and how to decide the value of the capacitors and resistors in any circuit like this?
Click to expand...
Since you do not understand the function of each part and how they were calculated in that very simple electronic circuit then how can we teach you about the basics of electronics in one post?? Most of us learned the basics of electronics in high school or from books and magazines then we learned the details in college or university.
 

The wattage of the speaker can be ignored, you can't buy one small enough to blow up! Your transformers, what you need to do is to feed an audio signal into one winding and measure what comes out of the other. If you have not got a signal generator, you could use a very low mains voltage from the SECONDARY of a mains transformer. If the transformer is a 12V one, get a 22k and a 1k resistor connect the in series, connect the free ends one to each winding of the 12V secondary. Now you have about .5V across the 1K resistor, solder a piece of wire to each end of the 1K and connect to the mystery transformer. Measure the voltages on all the windings and note them, then come back here and we will advise you.
Frank
Frank
 

anny999 said:
i have seen many circiuts for walkie talkie. is the circuit i have selected and attached below correct? should i go for it?
because i dont have time for trying and testing...it is just a mini project of mine. it need not be of very high range


i have taken this circuit from here

homemadecircuitsandschematics.blogspot.in/2014/06/simple-walkie-talkie-circuit.html

i have only got 2 days to build it..so plz help
Click to expand...

This is a very clever but primitive design for rejecting interference and low gain with only 4 transistors for a transceiver. ONLY 3 if you consider the output as a Darlington transistor.
View attachment 110939
Layout and most components , the selection is critical and dependant on layout, but the circuit is common in each stage and found elsewhere.

Not easy to duplicate for a beginner, but ok to simulate for learning.

I wonder how he made out with deadline.
 

anny999, the power this thing produces is so small you need not worry about the speaker power rating. You would struggle to overload even the smallest one!

Going onlyon appearances, the blue transformer is the one I would try. If you have a test meter, measure the resistance between the pins. The pair with the lowest resistance is the loudspeaker side, the other side should be several times higher resistance.

Brian.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top