I want to turn on a VCR to record a camera for a security system

Thread Starter

d1940u

Joined Feb 12, 2011
18
I am not a electronic person. I want to turn on a VCR to record a camera when a 12 volts loop circuit is broken. The VCR's that I have require a momentary switch be pushed for both the on/off and record. Can you help me with a electronic circuit that I can solder in where the mechanical push button switches connects. Thanks in advance for any help.
 
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wayneh

Joined Sep 9, 2010
17,134
I believe what you want is called a monostable, based on the 555 timer IC. That would accept the trigger event - the opening of tour loop - and then close a connection for preset time to simulate a button push.

Do you have access to the 12v (DC?) supply? This could work well for powering the 555 circuit.
 

Thread Starter

d1940u

Joined Feb 12, 2011
18
Yes, the loop circuit is a 12 volt DC battery with a maintenance charger. There is also a 120 volt supply that is triggered on when the loop is broken.
 

wayneh

Joined Sep 9, 2010
17,134
Welcome to the AAC forum, by the way.

There's a reference at this site to a range of 555 circuits. Hopefully someone that knows were it is will chime in and point you there.

How sure are you that you can get at the switch contacts inside? Is it a mechanical switch or more like a touchpad button, like a calculator? Touchpad switches can be very tough to hack into - their signals are often sent over paper-thin ribbon cables, for instance - and there might not be an easy way to find access to the contacts.
 
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Thread Starter

d1940u

Joined Feb 12, 2011
18
Thanks for the welcome. Yes, the push button switches are soldered onto the printed circuit board.
I could use the remote if someone knows how to make that work.

I did a search for monostable and did not find a direct application. Thanks for your help
 

Thread Starter

d1940u

Joined Feb 12, 2011
18
As I have said I am not an electronic person. Reading about monostable, I only found ones that had a voltage output. Since I know nothing about the circuit on the VCR I was hoping to get a circuit that that provided a one shot switch using 12 volts for input that I could replace the push button with. Do you know of other forums that might provide help.
 

Thread Starter

d1940u

Joined Feb 12, 2011
18
I will read and understand. I am unsure how you electronic types decide to name your circuits. I would have never guessed that a 555 monostable multivibrator was a one shot switch.
Thanks again, at 70 I doubt that I will master electronics

 

wayneh

Joined Sep 9, 2010
17,134
I have read the article and do not see where the two inputs for the switch to go. What am I missing.
That depends on how the existing switch works; probably by completing a circuit to either ground or to a DC voltage, such 3.3, 5 or 12v. Probing it with a voltmeter should tell you if either pole is "hot", and what the voltage is. The output from the circuit in that article might be used directly by applying it the right pole. Note that this approach requires that the timer circuit and the VCR share a ground. In other words it acts a lot like a switch, under the control of a voltage at the gate.

Another approach - also requiring a common ground - would be to trigger a MOSFET with the timer's output. You still need to know which pole is at a higher voltage than the other. The trigger signal goes to the gate of the MOSFET thru a resistor, say 1k. The source goes to the lower voltage pole and the drain goes to the other pole. When "off", the MOSFET resistance is very high, but it switches to a very low resistance in response to a positive trigger voltage.

The best approach may be to use a solid-state-relay, or SSR, since this would allow the power supplies to be isolated. I've never used one, so I'd like to see someone else jump in here. There are also opto-isolators that might be appropriate here for the same reason.
 

Thread Starter

d1940u

Joined Feb 12, 2011
18
Thanks, I am beginning to understand what you are talking about. The reason I am trying to do this with a VCR is that I have a home, a cabin and a park model I would like to monitor if broke into. VCR's and camera's are cheap so I would like to have a recording if someone enters. I would like to have a switch I could solder in so I would not have to modify the circuit for a different model of VCR.
 

Wendy

Joined Mar 24, 2008
22,358
Lets go over what you want to do. I wrote the article in question, and I'm 54. :p

For the sake of argument, let us say you have a couple of wires from play connected and feeding out of the VCR. What is going to turn the VCR on and off?

You mentioned a 12V loop, could we have a bit more detail about that? It seems a simple relay may be needed. What breaks the 12V loop? A magnet and reed switch?

We help folks of all stripes here, and don't mind questions from beginners, so feel free. This is a safe zone for beginners.

Have you ever handled a soldering iron?
 
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Thread Starter

d1940u

Joined Feb 12, 2011
18
Thanks for the help

Yes, I have soldered printed circuit boards on small projects.

I have a loop circuit with magnet reed switches at each door inside and out. A 12 volt battery supply's the circuits. I have a cheap X10 security system that starts the lights,camera and siren.

"For the sake of argument, let us say you have a couple of wires from play connected and feeding out of the VCR. What is going to turn the VCR on and off?" I need a monetary switch.

The VCR's I have tried all have a spring loaded push button that starts the unit. Holding the push button in will not start the unit. The units starts when switch is opened.

Thanks again for any help
 

Wendy

Joined Mar 24, 2008
22,358
If you press the record and play button together, and hold them down, will it work the way you want? If this is the case you can simplify the circuit a lot.
 

Thread Starter

d1940u

Joined Feb 12, 2011
18
Not sure if I can release them manually at the same time. I believe the on will have to be release a little before record.


I tested and the on must be released before the record. The reason I want to turn on is we have power outages all the time.



What type of circuit do you have in mind?
 
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Wendy

Joined Mar 24, 2008
22,358
Actually I was thinking what would happen if you left them both pressed. Would it record like you want? I think it might.

Then the question becomes do you want it to stop?
 

Thread Starter

d1940u

Joined Feb 12, 2011
18
No if they are left pressed it stays off. The two circuits both start on release of button. Thanks for thinking


Is there another website you would recommend to find an answer?
 
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Wendy

Joined Mar 24, 2008
22,358
I can give you the answer, but I needed the information to know how to go about it. The equipment is over there, after all. Anyone else designing it would need the same information.

I'll sketch up the circuit in a bit. Basically your loop triggers a simple monostable, which pulses a relay. Looks like a 555 will be needed (or an equivalent).

I asked it before, but do you want it to stop? If so, on what setting (time or trigger)?
 

Thread Starter

d1940u

Joined Feb 12, 2011
18
I am sorry I did not answer the question, no it is not necessary to stop. If I find I want to stop it, I can shut off the 120 volt with my present alarm system.

A couple of stories about when I was broke into. They were there so long they took the intake manifold and heads from my boat. Another time my neighbor wanted to store a new couch in my cabin during the winter while they work on their place. She followed a truck out the road and thought to herself they have a couch like mine. Unfortunately it was her couch and she couldn't give a good description of the truck.

Sure hope if they get in again I will have a picture.
 
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