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I'm new to electronics in general...how would i go about doing this?

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krogersaurus

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Ok, so I've been reading my "electronics for dummies" book for a while and I just finished
Reading all about IC's. I have been especially interested in the 555 timer. I read about how to make a certain circuit called an "astable multivibrator". From what the book tells me, by
Setting up the circuit, I can create square waves that come out of the 3rd pin on the 555. TheBook included a formula on how to find how long the high and low parts of the wave. using my mathematical genius, I determined how to make a square wave which had a high part that would go for about 600 seconds, and a low part of about 300 seconds (so, it completes a cycle every 15 minutes). The timer was created to set off one of those annoying cards that sing every 15 minutes. I would love to hook the output up to the card directly, but the problem is that I am using a 9V battery for the circuit with the 555, and 9V would completely fry the card. So, instead I decided that I would just put the card and its battery (3V) on one open circuit that would set off the card if it were closed, and the 555 astable multivibrator on another circuit that has the output connecting to the ground, which is in this case the (-) terminal of the 9v battery. Is there some mystical device I could put into the set of circuits so that it would close a switch when current runs through another part of it. Like an IC with 4 pins, and the 1st pin connected to the output of the 555 and the 2nd pin connected to the (-) terminal of the 9V battery. Then the other two pins act like a push-button switch, except without the "push-button" part, and the switch closes to complete the circuit with the card.

Does this exist? Is there another way of doing this? Am I making any sense at all?!?
please help me...
 
Ok, so I've been reading my "electronics for dummies" book for a while and I just finished
Reading all about IC's. I have been especially interested in the 555 timer. I read about how to make a certain circuit called an "astable multivibrator". From what the book tells me, by
Setting up the circuit, I can create square waves that come out of the 3rd pin on the 555. TheBook included a formula on how to find how long the high and low parts of the wave. using my mathematical genius, I determined how to make a square wave which had a high part that would go for about 600 seconds, and a low part of about 300 seconds (so, it completes a cycle every 15 minutes). The timer was created to set off one of those annoying cards that sing every 15 minutes. I would love to hook the output up to the card directly, but the problem is that I am using a 9V battery for the circuit with the 555, and 9V would completely fry the card. So, instead I decided that I would just put the card and its battery (3V) on one open circuit that would set off the card if it were closed, and the 555 astable multivibrator on another circuit that has the output connecting to the ground, which is in this case the (-) terminal of the 9v battery. Is there some mystical device I could put into the set of circuits so that it would close a switch when current runs through another part of it. Like an IC with 4 pins, and the 1st pin connected to the output of the 555 and the 2nd pin connected to the (-) terminal of the 9V battery. Then the other two pins act like a push-button switch, except without the "push-button" part, and the switch closes to complete the circuit with the card.

Does this exist? Is there another way of doing this? Am I making any sense at all?!?
please help me...

You want a transistor. Your book should hopefully provide a better explanation than i can, but connect the base of the transistor to the 555 pin 3 via a small resistor around 100 ohms (i don't know just guessing the value here), the collector to the cards positive pin, and the emitter to the cards battery positive. Hopefully that should work.

Damian
 
Yes, a transistor will do the job but 100R is a little overkill for a base resistor for a transistor controlling a tiny current.

I would use a transistor with a high value base resistor - 1M should do it.

Another option is to use a CMOS 7555 timer which will be able to run of the same battery as the card so you can connect the card to its output.
 
but dont transistors have 3 leads? if i use two of them as a gate for the card, and the third one being fed by the output of the 555, where does the current from the 555 go? it has to go somewhere, and that somewhere is into the card circuit. wouldnt that fry the card anyways?
 
but dont transistors have 3 leads? if i use two of them as a gate for the card, and the third one being fed by the output of the 555, where does the current from the 555 go? it has to go somewhere, and that somewhere is into the card circuit. wouldnt that fry the card anyways?

It depends on how you have the circuit set up.


If use a 7555 run off 3V you connect the card as the collector load.

If you use 9V for the 555 circuit then you need to know which side of the switch on the card is positive and which is negative. The negative goes to the emitter and the positive to the collector.

You could use a DVM to measre the voltage across the switch contacts to find out which is positive and negative.
 
The device I think you're talking about its commonly known as a relay - it's just an electromagnet which activates a switch.

You can connect it to the output of your 555 but you'll need to connect a diode in reverse parallel with the coil to absorb the high voltage spike created when the relay is turned off.
 
The device I think you're talking about its commonly known as a relay - it's just an electromagnet which activates a switch.

You can connect it to the output of your 555 but you'll need to connect a diode in reverse parallel with the coil to absorb the high voltage spike created when the relay is turned off.

a relay you say? ill look that up.
it seems like a very plausible idea, but what exactly do you mean by reverse parrellel? (again, im new with all this stuff)
 
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