Will this work? - Electronic Circuits Projects Diagrams Free

daviddoria · 6th May 2003, 04:01 PM

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?

john1 · 6th May 2003, 11:55 PM

Hi daviddoria,

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

John

john1 · 7th May 2003, 12:13 AM

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.

John

daviddoria · 7th May 2003, 03:19 AM

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.

http://www.bandtank.com/david/tx-rx.wmf

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.

Sebi · 7th May 2003, 06:23 AM

The "transmitter" can't wok, because the NPN transistor base floating or go to negative via pushbutton.

daviddoria · 7th May 2003, 11:26 AM

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?

john1 · 7th May 2003, 07:11 PM

Hi Daviddoria,

OK.

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.
John

john1 · 7th May 2003, 07:48 PM

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.

John

john1 · 7th May 2003, 08:31 PM

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.

John

john1 · 7th May 2003, 09:45 PM

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
fine.

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.

John

daviddoria · 7th May 2003, 10:24 PM

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

)

http://www.bandtank.com/david/newtx-rx.wmf

thanks guys

david

john1 · 7th May 2003, 10:58 PM

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

john1 · 7th May 2003, 11:23 PM

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

daviddoria · 8th May 2003, 12:41 AM

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?

thanks
david

john1 · 8th May 2003, 01:48 AM

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

note:
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.

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6th May 2003, 04:01 PM	(permalink)
daviddoria	Will this work? 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? __________________ thanks, david

6th May 2003, 11:55 PM	(permalink)
john1	Hi daviddoria, I think you will have to post a diagram. Sorry, but your description is not detailed enough. John

7th May 2003, 12:13 AM	(permalink)
john1	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. John

7th May 2003, 03:19 AM	(permalink)
daviddoria	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. http://www.bandtank.com/david/tx-rx.wmf 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. __________________ thanks, david

7th May 2003, 06:23 AM	(permalink)
Sebi	The "transmitter" can't wok, because the NPN transistor base floating or go to negative via pushbutton.

7th May 2003, 11:26 AM	(permalink)
daviddoria	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? __________________ thanks, david

7th May 2003, 10:24 PM	(permalink)
daviddoria	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 ) http://www.bandtank.com/david/newtx-rx.wmf thanks guys david __________________ thanks, david

7th May 2003, 10:58 PM	(permalink)
john1	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

7th May 2003, 11:23 PM	(permalink)
john1	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

8th May 2003, 12:41 AM	(permalink)
daviddoria	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? thanks david __________________ thanks, david

8th May 2003, 01:48 AM	(permalink)
john1	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 note: 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.