Thanks for the response I will try your advice.

Mike.

? manifold wrote:

Do you already have the 555 circuit built?
Are you using an lm555 or an lmc555?

The 555 is an excellent part to use to start learning electronics.? I
would also suggest that anyone with an interest in electronics look
up the history of the 555 timer and understand its significance to
semiconductor production and marketing.? I do not think we would have
computers on our desks if the 555 had not been a great success.

There are lots of ways to do it.? This circuit is fairly easy if you
have access to both positive and negative leads of the bell.? If one
connection is permanently connected to ground then a different
circuit can be used.

I will describe the circuit since I am not sure if I can post
attached schematics to the list.? This should work for the LM555; the
LMC555 has lower output current and may not drive a low beta
transistor.

Parts:
R1, about 400 Ohms
D1, diode, 1A rectifier or switching diode,
Q1, an NPN transistor,
??? general purpose,
??? collector current (Ic) greater than 1 amp,
??? beta greater than 50
??? Vce greater than 30V

Circuit:
Connect the output of the 555, pin 3, to resistor, R1
Connect the other end of R1 to the transistor base.
Connect the emitter to ground (-).
Connect one end of the bell to +6V.
Connect the other end of the bell to the transistor collector.
Connect the cathode of the diode to the positive bell connection.
Connect the anode of the diode to the negative bell connection.

?? The diode is used to keep an inductive 'spike' from the bell from
damaging the transistor.? Put the diode as close to the bell as
possible.? If the bell is not an electromagnetic bell, then you
probably do not need it

It should work well.? Measure the voltage at the collector when the
bell is ringing.? It should be very low (0.1V to 0.25V).? If not,
then either the bell is passing more current than 1A or the
transistor is not switching on completely.? Reduce R1 and try again.?
Do not exceed the output current of the LM555 which is I think 200mA.

In this circuit the base current = the 555 output current is:
(12V - 0.7V)/R1

--- In Electronics_101@y..., emdgp30@y... wrote:
> Hi my name is Mike and I am new to the list. I am a tinkerer and
like
> to build circuits for my hobby of model railroad. What information
do
> I need in order to design a transistor output from a 555 timer
> output, to operate a bell that draws 1 amp at 6 volts dc. The
> initiating voltage however is 12vdc for the 555 timer circuit.
>
> Thanks Mike



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hello, could anyone explain me the following ?? 1. how do the waves actually travel through air ? ( for eg. waves in a radio receiver ) 2. why dont these waves mix up ? how is it that same waves are received after tuning the receiver ?? 3. what does bandwidth actually mean ? what is meant by purchasing bandwidth? please suggest some links if possible ?? i am a student of engineering and have studied all types of modulation techniques in college theoretically ..but i always wonder or rather dont understand how one can actually transmit sound and pictures through air.. i want to clear my basics about all that .. please help me... practical answers are expected 'cos i know evrything in theory but still know nothing. rahul...

Do you already have the 555 circuit built?
Are you using an lm555 or an lmc555?

The 555 is an excellent part to use to start learning electronics. I
would also suggest that anyone with an interest in electronics look
up the history of the 555 timer and understand its significance to
semiconductor production and marketing. I do not think we would have
computers on our desks if the 555 had not been a great success.

There are lots of ways to do it. This circuit is fairly easy if you
have access to both positive and negative leads of the bell. If one
connection is permanently connected to ground then a different
circuit can be used.

I will describe the circuit since I am not sure if I can post
attached schematics to the list. This should work for the LM555; the
LMC555 has lower output current and may not drive a low beta
transistor.

Parts:
R1, about 400 Ohms
D1, diode, 1A rectifier or switching diode,
Q1, an NPN transistor,
general purpose,
collector current (Ic) greater than 1 amp,
beta greater than 50
Vce greater than 30V

Circuit:
Connect the output of the 555, pin 3, to resistor, R1
Connect the other end of R1 to the transistor base.
Connect the emitter to ground (-).
Connect one end of the bell to +6V.
Connect the other end of the bell to the transistor collector.
Connect the cathode of the diode to the positive bell connection.
Connect the anode of the diode to the negative bell connection.

The diode is used to keep an inductive 'spike' from the bell from
damaging the transistor. Put the diode as close to the bell as
possible. If the bell is not an electromagnetic bell, then you
probably do not need it

It should work well. Measure the voltage at the collector when the
bell is ringing. It should be very low (0.1V to 0.25V). If not,
then either the bell is passing more current than 1A or the
transistor is not switching on completely. Reduce R1 and try again.
Do not exceed the output current of the LM555 which is I think 200mA.

In this circuit the base current = the 555 output current is:
(12V - 0.7V)/R1

--- In Electronics_101@y..., emdgp30@y... wrote:

Hi my name is Mike and I am new to the list. I am a tinkerer and

like

to build circuits for my hobby of model railroad. What information

do

I need in order to design a transistor output from a 555 timer
output, to operate a bell that draws 1 amp at 6 volts dc. The
initiating voltage however is 12vdc for the 555 timer circuit.

Thanks Mike

I am new to this group and new to electronics, (aside from the occasional
small repair) I am the kind of person who learns by doing rather then just
reading. So i was wondering if there are any good project books or websites
which would be a good place for me to start. As I said I would rather learn
things by doing rather than starting off with only extensive electronics
laws and theory. Thanks

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Yes, that's about right but there are few points that were missed.
Usually the Vbe drop of the transistor is inside the feedback path so
it does not appear at the output. This works for regulators that
have a Vref input or regulators that are adjustable like the LM317.

Ok, so you may be asking yourself, "why don't I buy a cheap low
current regulator and use a series pass transistor to increase the
current to whatever I want?" The problem is that you lose important
features designed into the regulator like foldback current limiting,
thermal limiting and short circuit protection. In the series pass
configuration the regulator only has the transistor base current
going through it. It does not "see" the load current or thermal
dissipation of the transistor and so has no control over it under
abnormal or fault conditions.

Here's a link that shows both NPN and PNP series pass elements
connected to an LM317.



--- In Electronics_101@y..., Jim Purcell <jpurcell@w...> wrote:

d,

suggested bypass transistors as a method for limiting current at

the input

to LM3xx and LM78xx voltage regulators.

First off, maybe you mean a pass transistor. This approach involves

using the

regulator to establish the output voltage at the base of a power

transistor,

then the power supply output is taken from the collector. The

unregulated DC is

applied to the collector. So the transistor isn't a special device

except that

it is designed to operate at higher current than the regulator. In

that sense

the input current to the regulator doesn't need to be large because

the

transistor passes the current to the load, not the regulator. Of

course the

actual output voltage will be the regulator voltage minus about 0.7

V, the

normal BE drop on a silicon transistor. Some circuits use more

complex

regulators that use the actual output voltage to control the base

reference

voltage.

Jim

What are bypass transistors and how do they work? What types are

good for

this?

-Mike

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Hi All,

Does anyone have experience using an ICL8038 waveform generator to
produce audible frequencies (for musical purposes)? I've looked
through the spec sheet for this chip, and it is very thorough, but
meant for someone with a lot more experience than me! :-)

Most schematics I've found so far seem to be meant for 10kHz+ range
purposes beyond my comprehension :-P

All I need is a simple formula for frequency, so I can pick the
appropriate resistors/capacitor combination for an audible sine wave.
Can anyone help me out? Does anyone have a schematic for producing
hearing range sine waves using the 8038? I'd also like to do "fine
tuning" modulation of the frequency using a 2nd chip (for vibrato and
additive synthesis effects), so if you know how to do that, please
let me know, it seems to involve pin 8, but I'm not sure.

I imagine I can just use a transistor to amplify the signal enough
for a line-level input to a stereo amplifier... (please tell me if
I'm wrong here...)

Thanks!

Tako Oda

first of all hacking is illegal
and with the digital milenium copy right act you can get in alot of
touble....plus hackers just dont give up there secrets....if you want
to learn how to hace start studing programing and systems including
there architecture
jason

I'm kind of wondering what prompted you to make such a request... Are
you interested in learning how to circumvent computer security? If
so, I hope you enjoy reading big giant books and poking frustratingly
at servers and operating systems for sometimes 30 hours non-stop...
It's a hobby a do -not- recommend taking up late in the game...
Hacking charges can get you the same jail penalties as a SERIAL
RAPIST... Scary, huh?
-Shad

ejazabidi,

i need to know about "HACKING AND HOW TO HACK".
is there some one how help me.

If you don't know how to hack, you probably don't want to do it. If you are
talking about breaking into computer systems and the like. The term 'hacker'
actually has no connection with the hacking you are probably talking about.
It's just that some hackers, i.e. people who like to play around with
computers also do the nasty kind of hacking. If I knew how to do it I would
never tell anyone.

Jim

ejazabidi,

i need a circuit which convert my monitor into tv receiver.
i will be very thankfull.

That's not very easy to build. On the other hand they do make TV cards that
you can use to watch TV on your computer. In the States, they run between $75
and $150, depending on features. Check your computer store.

Jim

Victor,

I am victor from Malaysia.

Hi Vic. :-)

Is there any way that 2 persons can communicate with each other via 2 way
radios ( or any other suggestions ? )

Yes, now the communications laws in Malaysia are probably different from
those in the US, I have two Radio Shack low power transceivers that operate
on 49 MHz. I don't know their range, I've never used them except room to room
in my house. I got them so I could check which circuit breakers control which
lights and outlets in the house. If you have any electronics stores near by
and your radio laws allow you can probably buy a pair of radios.

in city without using pay phones ?

Now the range of these small radios is limited. Anything that is long range
usually requires some kind of license. The stores selling that kind of radio
can tell you about the rules.

I don't know much about the " range " as stated in the advertisement ?
is this the locus point straight-line range ?

That's probably something in a similar radio band. higher frequencies are a
bit more directional. They are not always line of site but at least short
range, about 1/4 th of a mile. I guess that's less than 1/2 a kM.

Jim

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helo
i need to know about "HACKING AND HOW TO HACK".
is there some one how help me.
thanx.

helo
i need a circuit which convert my monitor into tv receiver.
i will be very thankfull.

开云体育

Hai,

I am victor from Malaysia.

Is there any way that 2 persons can communicate with each other via 2 way
radios
( or any other suggestions ? )

in city without using pay phones ?

I don't know much about the " range " as stated in the advertisement ?
is this the locus point straight-line range ?

since I am an accounting grad.

thanks a lot

best wishes
vic

It is correct that fuses are in units of Current.
Power(watts) is in units of (AMPS)Current and volts. POWER=VOLTS X CURRENT
FUSES PROTECT CIRCUITS (IF SIZED CORRECTLY) WHEN THE Amps is sufficient to "blow" the fuses.

If fuses were sized in Power (watts) they would have to be rated for a certain current, AND voltage and there are many combinations that one could come up with for a certain power rateing.

ie. (power =60watts} could be a current of 1A at 60 Volts, or 60amps at 1 Volt, or 20Volts at 3 Amps. etc so it would not make sense to rate them using power (watts)

From: "Guillermo Brajovic" <guillermo.brajovic@...>
Reply-To: Electronics_101@...
To: Electronics_101@...
Subject: [Electronics_101] Re: Fuses
Date: Sat, 27 Oct 2001 22:35:23 -0000

Can anyone answer my original question - Why are fuses not rated in
units of power?

As fuses are used as overcurrent protection devices, the relevant
factor here is the CURRENT that the fuse will carry before melting.
Power is somewhat irrelevant here, as it would be an indirect way to
tell you the important parameter, the current capacity.

I cannot recall anyone designing a circuit saying "then, I want the
fuse to blow while it dissipates 10W or above", but " I want the the
fuse to blow while 10A or above go through this path".

Also, power alone is useless, you need also the resistance of the
fuse to calculate the current capacity, or the voltage drop across
the fuse.


Guillermo.

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Hey, just found this group. I'm sure it's going to be great.

Here's a website with some very good electronic circuits: