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Will this work?

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I will post a drawing later, but for now lets see if my description works.

The idea is when you push the button on circuit A, the LED on circuit B turns on.

Circuit A

A battery is connected to a momentary switch that turns the whole thing on when it is pressed. The switch then is connected to the base of an NPN transistor through a current limiting resistor. The collector is connected to the (+) battery terminal. The emitter is connected to a LC circuit (parallel) that controls the wave frequency.... still wondering what to do with the (-)...

Circuit B

The exact same LC circuit as in circuit A is used as the first stage of circuit B. The output of the LC is connected to the base of an NPN transistor. The collector is connected to a new battery (as the circuits will be separated). The emitter is connected to an LED through a current limiting resistor. The negative of the LED is connected to (-) battery.

will that work?
Hi daviddoria,

I think you will have to post a diagram.
Sorry, but your description is not detailed enough.

Hi daviddoria,

sounds like this might be a small transmitter and receiver,
working an LED on the receiver.

"When you push the button on circuit A, the LED on circuit B turns on"

Well, the LED will go out when you stop pressing the button,
is that ok?

If the distance between the two assemblies is small,
then the receiver circuit need be little more than a small ariel
and an LC, with the LED on it, like a wave-meter.

If the distance is more than a room, you may need a stage or two
of tuned amplification, not just amplifying the output from the LC.

If you make the output of the oscillator more than half a watt,
you may infringe the regulations in some countries.

naa this is just to go 20 feet or so... i dont think that'll infringe on anything ;)

ok, so this doesn't work... now the question is what's wrong.

thats what i did... is it because the coils I made are not exactly the same?

should i replace the cap in the transmitter with a variable cap so i can try to get the time constant out of the LC circuits the same?

any advice is much appreciated.
The "transmitter" can't wok, because the NPN transistor base floating or go to negative via pushbutton.
if i connect the base to the (+), then where do i put the (-)? or what do i run to the base to give it a signal to amplify to spit out to the LC?
Hi Daviddoria,


Lets start with the transmitter,
how many turns on the coil,
and what dia roughly?
What sort of frequency do you want,
or dont you care?

Have a look through the attached.
I'll be here for a while.


  • BasicTrCct.jpg
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Hi Daviddoria,

Heres another picture to contemplate.

When coils are in close proximity like this,
they are intended to influence each other.
Sometimes they are wound on top of each other.

It is worth mentioning that only changes in
current cause any effect between the coils.

More in-depth explanations can be found easily.



  • Coils.jpg
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Hi Daviddoria,

Heres a bit more to contemplate.
In this arrangement any changes in current through the larger coil
cause currents in the smaller coil.
Currents in the smaller coil cause currents in the E-B junction.
The transistor alters its collector current, causing changes in the
larger coil.

A simple oscillator like this is almost guaranteed to work,
but without tuning it could be at any fairly high frequency.

When oscillating the current drawn from the battery will be low,
as the coils assume a high impedance to high frequencies.

If it doesnt oscillate, reverse either winding, it requires
positive feedback, the limiter will prevent damage.
More detailed explanations of oscillators can easily be found.



  • Oscillator.jpg
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Hi Daviddoria,

By adding a small trimmer across the collector coil
the circuit now assumes the familiar appearance of
an LC tank and tickler.

The L & C form a resonating unit which determines
the frequency of oscillation.

There are many types of oscillator, a quick search
will bring up many.

To assist radiation (propagation) a small ariel can
be connected to the collector, or another winding
for it. The loading and propagation of radio waves
is a lengthy study of its own, but for a small low
power assembly like this, approximations should be

The reciever should also be tuned.
just making it the same will not do.

If you are going to make a small oscillator like
this, i suggest you do it in the same room as an
operating television. When its oscillating you
should see the patterns on the picture.



  • OscillatorTuning.jpg
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wow john sounds like you are extremely knowledgeable in this field.

i though of the trimmer caps right before i read this hehe :) really i only need it on one of the circuits though correct? because i can tune one to the other one's constant frequency.

That is the receiver you drew correct? in my drawing, my 2 coils where in series, where yours are in parallel. 1) what is the second coil for? 2) why do you hook up the LC circuit to the collector of the transistor? and what is going to the base (i guess that is kind of question 1)

also, in my transmitter circuit, thinking about it now isn't it ok to connect the switch to the (-) terminal?

here are my new drawings (note my coils still in series (physics teacher suggestion, i'm sure you know more than him though :))

**broken link removed**

thanks guys

Hi Daviddoria,

Thank you for your confidence in me.
I hope i deserve it.
Could you give me a comment on my earlier post please?
The one with the transistor and the (lamp) bulb.

Cheers, John
Hi Daviddoria,

Could you describe the coils in your transmitter circuit please.
What dia roughly?
Are they on the same former ? (tube)
Are they close together?
Are they the same?
How many turns roughly?

Cheers, John
john... i'm not sure i understand your bulb circuit, thats why i had not commented.

also, all 4 of my coils are 6 turns of 22 AWG wire around a 3/32 inch drill bit.

can you please explain what the 2nd coil in both circuits does and why it should be placed in series/parallel.

the only other thing is still why connect what you did to the collector and base.... do you have AIM or IRC or something where we could talk real time sometime in the next couple of days?

Hi Daviddoria,

Thats quite a high frequency for a beginner.
Too many things start to affect high frequencies like that.
I would suggest 8 turns for the collector coil,
and 5 or six for the base coil, both at about 5/16" and
if the wire is not insulated, make sure the turns are not
touching each other, but both coils next to each other.

I am sorry i did not make the transistor and bulb example
very clear.
If you want to understand circuits, i will have to explain
the action of a transistor better.

That circuit is just an illustration to show that a small
current through the E-B junction allows a greater current
through the E-C junction.

This means that variations in a small current can be copied
in a larger current going through the collector, this is
called 'Gain'

A transistor with a gain of 20 would give a current change
20 times greater through the collector, from the current
through the base.

The little box in that drawing of the bulb and transistor
shows two little arrows.

Those arrows show the current paths, one through the base
and one through the collector.

If this is still not clear, i will try to explain it in
a different way.

Best of luck, John

the second smaller coil is to pick up the current changes
in the collector coil, and feed them back to the base,
which controls the current through the collector. The
current quickly reaches a point where it wont increase
any more. The change then stops. It is the change that is
fed back, and when the change stops the collector current
starts to fall, because it was partly helped up there by
the coil on the base. When the collector current starts
to reduce, that change is picked up as a change by the
coil in the base, and some signal is given to reduce the
collector current. So the collector current reduces more,
that change of current is seen by the coil in the base
and more signal is sent to further reduce the collector
current. The collector current quickly reaches a point
where it wont reduce any more. So it stops reducing.
Then there is no change in the collector current, and the
coil on the base no longer picks up any change. The
signal from the coil on the base stops, the collector
current starts to rise. This change is picked up by the
small coil on the base, which instructs the collector
current to increase. This action means that the circuit
swings backwards and forwards from low current to high
current, it is an oscillator.
This current doesn't go backwards, its just a changing
forward current through the transistor. It is often
treated as AC and in a lot of ways its OK to do so.
i think i understand the receiver now, please have a look at
**broken link removed**

however, the transmitter i am a little confused still...

here is my understanding of a transistor:
a current is applied to the collector, but only let through to the emmiter when there is also a current applied to the base.

is that correct?

so in this receiver application.................

wait, while typing this i thought of something. am i understanding right which is receiver and which is transmitter? In my link above, if my receiver is even a receiver, won't my LED flicker at whatever freqency we are receiving at?

I would imagine we also need an oscilating circuit to receive an oscillated wave, but i am still confused.


do you maybe have a link to a good page about this stuff... i can't seem to find anything this basic anywhere. everything i find about transmitting is extremely more involved than these circuits. they are all involving logic and transmitting codes and things like that. i will get into that eventually, but right now i just want to have an on/off type of receiver/transmitter.

thanks again

a current is applied to the collector, but only let through to
the emmiter when there is also a current applied to the base.

Well sort of, yes.
But you dont get any flow until there is pressure.

The usual arrangement is that you set some pressure
across the E-C junction.

Then you cause some current flow through the EB junction.

This causes the resistance of the E-C junction to change
allowing current flow up from the neg to the pos.

It is a controlled change, if you go slowly from min to
max on the base, so would the current through the collector,
its not just on or off.
Hi David,

I found my way to that site, after a lot of 404s

It looks like you have the names backwards,
but the circuit looks workable,

providing that the two coils are together,
so that the one on the base,
can be influenced by the one in the collector.

Have you tried it?

Hi David,
Ive suggested a small alteration to your circuit,
which does look workable.

Have you tried it yet ?



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