Beginner in need of Help!

Discussion in 'Electronic Components' started by James, Jan 9, 2007.

1. JamesGuest

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-----O O-----

Can anyone tell me what I would need to produce a component that acts as a
switch - switching either on or off according to how much voltage is going
through the circuit?

James

2. Homer J SimpsonGuest

Be more specific.

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3. FredrikGuest

If the it's DC-current and voltage below 30V, you can use a comparator.
http://www.national.com/pf/LM/LM111.html

Find a point in your cuircuit where the voltage vary with the current and
connect it to one of the inputs. (If you can't find any put in a low value
resistor serial.)
Connect a fix voltage to the other input and you will have your signal on
the Output switching between open and ground depending of the current.

Good luck /Frederik

4. LostgallifreyanGuest

As Fredrik said, look at a comparator. (Or any cheap standard op-amp).

Also, look at discrete active components, the transistor, FET, thyristor
and triac. Any one of those might be suitable. By the time you understand
each of those well enough to choose the most suitable and apply it to your
problem, you won't be a beginner anymore. it won't take you very long to
work it out either, the more references you find online and can grasp
quickly (pass over those that look opaque, there are are always other
opinions and guides), the faster you'll grasp the rest and know which ones
are useless to you.

5. JamesGuest

What I want to achieve is hard to describe but I'll try. Say I've got a v
simple circuit that includes a power supply and a bulb. I break the circuit
and want to put something in its place - this component would measure the
voltage and, providing it was in-between set boundaries (i.e. between 0.4V
and 1.2V or between 2.4V and 2.8V) would complete the circuit. If the
voltage was not within ranges specified, the circuit would remain broken. I
hope this is clearer )

James

6. Homer J SimpsonGuest

How can it sense the voltage without applying voltage?

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7. Graham WGuest

Is this something to do with cycling ni-cads for RC Models?

8. JamieGuest

you need something called a voltage comparator.
look it up.
they come in various forms.
the LM311 is a comparator that works ok.
op-amps also can work as a comparator how ever,
some op-amps have full backs depending on how
complex you get and what you expect over all.

9. ehsjrGuest

______
V+ ----A B-----+
|
[Bulb]
|
Gnd --------------+

What you described means the circuit must sense
the voltage between points A and B. You *don't*
want to do that - your description is not correct.
Every time you close the contacts that connect A to B
the voltage between them drops to 0 and your sense
circuit can no longer determine whether the contact
should remain closed or should open.

What you *do* want to do is sense the voltage between
V+ and ground. When that voltage is within a specified
range, you want points A and B connected.

You can use a window comparator to meet the above
requirement. I think you want more detail than just
the words "window comparator", but more detail on the
requirements is needed to do that. What is the load
current? What is the maximum range of V+ ? What
are you trying to do? Someone replied suggesting
you might want to discharge a NiCd - if that is the
case, say so.

Ed

10. JamesGuest

What I really want to do is be able to send a digital signal (via means of a
series of switches on a control box) through a series of parallel circuits
each containing one lamp. Each corresponding signal or absence of a signal
(data) would then either allow or not allow power to the lamp (power.)

see
http://homepage.ntlworld.com/james.merrie/educational/physics/electronics/el
epic.jpg

Is the need for a digital set of electronic pulses what differentiates a
digital electric circuit from an analogue electric circuit? How can this be
accomplished with this circuitry?

I hope this is clearer

11. LostgallifreyanGuest

From my earlier post:

Look at discrete active components, the transistor, FET, thyristor
and triac. Any one of those might be suitable. By the time you understand
each of those well enough to choose the most suitable and apply it to your
problem, you won't be a beginner anymore. it won't take you very long to
work it out either, the more references you find online and can grasp
quickly (pass over those that look opaque, there are are always other
opinions and guides), the faster you'll grasp the rest and know which ones
are useless to you.

Specifically, look at the use of an NPN transistor on the ground side of
each load (lamp, in this case). It's a cheap, easy, standard method of
making a small signal (digital or analog) control a low-voltage DC load.
Look at the use of a transistor as switch, rather than as gain stage.

12. ehsjrGuest

You want an X-10 system. Google X-10.
It works by placing digital addresses and
commands on a 121 kHz signal which is placed
on the AC mains.

http://en.wikipedia.org/wiki/Digital

Ed

13. Peter BennettGuest

If you just want several switches to individually operate several
lights, (switch one turns on light one, switch two to light two...)
there is no logic required - just connect each switch in series with
its corresponding light, and connect all the switch/light pairs in
parallel across the power supply - see
http://members.shaw.ca/peterbb/sw-light.gif

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter

14. Homer J SimpsonGuest

No. Are you trying to build a "Magic Switchboard"?

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15. JamesGuest

I need all the switches to be located in one place

16. JamesGuest

Does such a component exist?

17. Mikkel LundGuest

James skrev:
Yes, get it at the Magic Shop.

18. JamesGuest

haha

If you looked more closely, you'd see I was after a circuit that would be
able to handle digital signals.

19. LostgallifreyanGuest

We looked plenty close, and gave you a magic potful of wrong answwers.
What's really funny is none of us are to blame. You're going to have to
spill the whole story of what you want, partly to frame the concept to
yourself so you have a clearer idea of what to ask, then to ask so you get
meaningful answers. So far you've been suggested a set of switches in
paralel, through transistors, op-amps and comparators, and a full-scale
digital system modulated onto the AC line, and we don't even know if you're
wanting your mains lamps switched, or a set of torch bulbs on a wodden
board for an educational project, because you won't tell us. And unless you
do, people will start to wonder if you're a troll baiting people into
looking like fools by sounding like they know the answer to a question that

20. Peter BennettGuest

replying to, and trim any unnecessary quoted material - thanks.

So - put all the switches and the power supply in one place, and run a
pair of wires (power from switch, and return to supply) to each light
- no electronics required. If all the lights are in one place, a
single return wire may be adequate, depending on the current drawn by
the lights, and the operating voltage.

If you have something more complex in mind, please give us more
details of your requirements. The better you specify the problem, the
more likely we will be able to give a useful answer.

How many light/switch pairs are there?
Are all the lights also in one place?
How far from the switches to the lights?
What type/voltage/power are the lights?

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter