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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