How to switch an AC circuit from a computer

[politcalconfusion]

Hello,

I want to use an embedded or a plug computer to control an electric home door lock. I don't have any of the components yet, but it looks like the lock requires a 16VAC power supply. Assuming the computer has a USB interface, would I use something like this -- http://www.obdev.at/products/vusb/powerswitch.html? And, if so, how would I mate the DC pins on the USB board to a switch on the AC circuit? I'm a total newbie regarding electronics.

Thanks,

Michael

 

[TBennettcc]

What is a 'plug computer', by your description? This can be as simple or as complex as you want to make it. When I first read your post, I was thinking about the magnetic door locks. From how I understand the circuit, it's basically a big coil of wire energized to become an electromagnet. There is a metal plate on the door, while the coil sits in the door frame. When the power is applied to the coil, it attracts the metal plate on the door, and you cannot open the door. When someone presses a switch, it temporarily interrupts power to the coil, de-energizing it, and allowing the plate to pull away from the coil. That seems simple enough to me. This could be expanded by using a relay to interrupt the power to the coil, and controlling the relay using some sort of output from your computer, maybe from the serial or parallel ports.

You say that you don't have any components, but at the same time, you say the lock requires a 16VAC power supply? How can this be? Are you looking at possible parts? Do you mean you have already ordered parts, but just don't physically have them yet? What parts do you have and/or what parts were you intending to use? Do you have a make and model number for the door lock? How does the lock work? Is it similar to the one I described, simply being energized and de-energized to prevent and allow entry, respectively? Or is there more to the circuit?

The more information we have from you, the better we can help. High-quality, clear, detailed pictures are ALWAYS appreciated. (You can link to a Flickr account if necessary; the file upload limits here are pretty small.)

 

[politcalconfusion]

This is a plug computer: http://en.wikipedia.org/wiki/SheevaPlug

This is the door lock I was considering: http://www.smarthome.com/5190/Electric-Door-Strike-8-16VAC-220/p.aspx

This is a compatible power supply for the lock: http://www.smarthome.com/5191/16VAC-10VA-Power-Supply-323-M/p.aspx

Here's a similar product at Amazon that also takes 16VAC.

I am assembling a parts list for someone else and have not ordered anything. He'll have to determine which lock fits in his door jamb. And he'll have an electrician install it. I assume that manual operation of the lock would just require placing a push-button switch in the lock's power circuit (i.e., on the lock's side of the transformer) that would release the lock for as long as the button is pressed.

I want to mimic the function of the push-button switch from the plug computer which only has a USB interface. The goal is to have a lock that can be remotely unlocked via internet communication with server software running on the plug computer.

 

[jackorocko]

The usb will supply 5 volts, That should surely turn on a transistor that will activate a relay or the lock mechanism itself. The hardest part may be to actually write the program to get the usb to send a pulse long enough to unlock the door.

Is it really your goal to only use this over the internet?

 

[(*steve*)]

It's probably best to look for various interfaces that connect to USB. Trying to interpret the USB signals yourself would be a much larger problem.

Here is an example of something that may do the job.

It is possible to build this type of stuff, but you're probably going to need a substantial amount of hardware and software experience.

It might be worth trying Sparkfun for something too. They have a lot of stuff and they range between a working devices and naked chips.

 

[politcalconfusion]

Thanks, (*steve*). I stumbled across this -- http://chezphil.org/slugpower/, which looks like it can do what I need if I could decipher the schematic and find an appropriate solid state relay. I can write application level code in C, but anything lower level would be a challenge.

 

[(*steve*)]

Yep, those chips have drivers already available, so no problems there

 

[climatex]

I've made this, folks. Dangerous for beginners and usually does not comply with all the safety standards your intuition tells ya, but it is a good proof-of-concept, anyway. Anyways, here goes. a standard serial port, some relay and a 230V mains appliance.

(The computer you have seen is not used everyday.)

 

[poor mystic]

If you can write in C, why not wiggle a pin on the printer port?