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A circuit to control another circuit

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RazB

New Member
Hello,
I have a 12(v) DC circuit of a lighting system for a model. At the moment it is all already built and there is a switch for every group of 1.2W bulbs (4 bulbs each), all the bulbs are in parallel. The power source is a 12(v)/8(A) transformer.

We want to have the effect of fading when the light turns off. This we achieved by using capacitors, one capacitor connected in parallel to each of the bulbs. However we want to control the effect and have it only when we want it. For that we did a test with relay devices, used for car electricity, connected to a 6(v) circuit. Here is an example (in order to make it easier to understand I made a smaller simpler circuit of 4 bulbs only):
2040-circuitk.gif

(Just to make things clear, the two circuits are separated and insulated).

Now the problem is that these relay devices are quite noisy and can not be used for the real project. Therefor I am looking for an alternative way rather than the relays to do that.
I heard that what I need might be transistors, but I have no knowledge of them or how to use them for the purpose. Do you have any idea?

Best Regards,
Raz.
 

ronv

Well-Known Member
Most Helpful Member
fader

How big are the capacitors? The 12 volts is dc? So you have rectified the output of your transformer? Here is a link to a spec. sheet for the solid state relay vne spoke of. It would need a resistor in series with the input to limit current and it might not be large enough to charge for your capacitor without damage. You might also consider a smaller relay as a direct replacement for your auto relays to reduce the noise.
http://www.clare.com/home/pdfs.nsf/www/LCA710_R07.pdf/$file/LCA710_R07.pdf
 

RazB

New Member
Thank you vne147 and ronv.
The capacitors are 1000µf. The transformer output is indeed 12(v) DC. What happens is that when a capacitor is connected to a bulb in parallel, as the light switch turns on, the capacitor charges as well, then when the light switch turns off, the capacitor discharges by the bulb and we get the fading effects.
The opto-isolator seems to be the device we are looking for. It is just like a non-mechanic relay. The specific opto-isolator device you gave me it's specs should work, the only thing we need is a resistor connected in series for each one because of the 6v source, am I right?

Thanks again,
Raz.
 

RazB

New Member
Oh my, I see these opto-isolators are quite expensive. We planned to put one for every single bulb, this is way too much. Is there some other option? or maybe there are silent relays that can stand at least 12(v)/0.5(A)?
 

ronv

Well-Known Member
Most Helpful Member
Fader

The opto isolators wouldn't like the big capacitor across the light either. This could be quite simple (and cheap) if you could run everything off the 12 volts. Is there some reason you can't do that?
 

RazB

New Member
It is not much about budget, it is more about rationality, isn't it insane to put a 6-12$ device on each little bulb which costs 2% of it? We are talking about 32 bulbs.
We wanted it to be controlled by another lower voltage circuit because we wish to have the whole thing controlled by a computer one day. Anyway - if we do use the same 12(v) circuit, I was told to use NPN transistors, which I don't really understand.
I was given this diagram:
2050-circuit2.gif

Do you think it would work if I have the same setup on every bulb? and is the only thing I need is to connect the new switch (left to the power source) from a point above it to the other setups to have them all controlled by that same switch?
If you have any other idea, I am all ears.

Best,
Raz.
 

vne147

Member
It is not much about budget, it is more about rationality, isn't it insane to put a 6-12$ device on each little bulb which costs 2% of it? We are talking about 32 bulbs.

$6-$12!?! I'm not sure where you found that price but there are MUCH cheaper alternatives out there depending on where you live. That's why I asked. Here is link with a bunch in the $1.25 - $1.50 range. I didn't dig through the list to see which ones would work for your specific purposes but I filtered it so all the results shown can handle an output current of .5A or more.
 
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vne147

Member

ronv

Well-Known Member
Most Helpful Member
Yes, But that should be ok because your 12 volt supply has a transformer. But maybe I should ask you what that circuit looks like.
 
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