This is about using a small signal to control a larger signal. Overall, here a small amt. of power will turn on a small switch that will turn on a much larger power switch.
Here I use an opto-isolator chip (isolates one circuit from another with a light emmiter and light sensor in one ic chip package) and a triac (rated for 120V ac or higher). The opto-isolator is used to trigger the triac (basically a solid state/semiconductor – transisor like – relay-switch) on which will allow current to flow through a device connected in series to its power terminals/pins. The current to the opto-isolater must be limited just like most led diodes to prevent burning it out, the same for the triac control/gate signal. As can be seen in the video, few parts are necessary to make a cirucit like this.
5V is a typical signal from computers, such as the parallel port/printer port and the USB ports. The system can be set up to work with other voltages simply by increasing the resistance of the resitors if the on/off control signal is of higher voltage.
If you want to look on Google for the data sheet of the Opto-Isolator , look up MOC 3010 and similar chips. You can usually find some of them for under a dollar these days.
The triac is basically like an open circuit (high resistance) when in off mode, so that is why I measured 120Vac across its power switching terminals. Then signaled to turn on with some voltage and current at its gate terminal, it turns into a much lower resitance, much like a closed switch, but it’s not perfect it does have some voltage (”loss”) across it since it’s made of a semiconductor material and not metal like a switch inside. The voltage measured across the triac when switched on was about 2Vac as seen in the video.
You don’t have to use a triac either, but maby a scr or other device, the choice is yours and depends what you are making.
This circuit/setup was for experimentation, however if you make something like it, you will have to put the circuit into a box that will also contain a “wall socket” where the 120Vac device can simply be plugged into, this is for safety and convenience of the user of the circuit.
Here is a closely related video with a helpful circuit diagram: http://www.youtube.com/watch?v=5tt4zAkpDPw&feature=related
If you want to switch DC (perhaps 12Vdc as for car battery circuits/alternative power, etc), even with high current, here is a good video from the johnarrons channel that uses a solid state relay all contained in a small package: http://www.youtube.com/watch?v=paJj66UW7C8
Connecting a circiut like this shown in the video to the parallel/printer port is somewhat common. Let us here on YouTube know the simplest method to connect a circuit like this to the USB and be switched on/off. (I read it’s difficult or impossible to switch the USB 5V power on/off. Anyone interested in electronics would appreciate it if you know of a program/code that can). Maby it might need a small circuit board but would require “chips” which would complicate and increase costs, but a premade cheap USB device can also be utilized I believe. Leave a comment if you know or have ideas. I’m thinking now that if a small/cheap premade circuit is available that it probably would not switch the USB 5V line on/off as is, but maby it could send/have a small controllable signal that can be utilized can switch something on like a transistor, scr, triac, etc.
I make the vid in an area with a circuit breaker, and choose the area shown in the video. The circuit breaker is a “ground fault” one, that can be easilly reset, at the wall socket. Up to you if you want to do this or have some circuit breaker box available for projects.
Basically, with a parallel port/printer port cable, you can typically control (set on/off) 8 devices/circuits (without additional circuitry and complexity) like this, but sending signals or data signal (with some computer program) to the printer port. Typically its some program code like:
OUT port# digital_number_needed.
Perhaps you want to turn the devices on/off at certains times, etc. Some printer ports allow data signals to be sent through them to the computer also. Maby some signal can be sent to the computer and then a signal can be sent out to turn something on or off.
A possible use is manual (without a computer) remote switching using low voltage wires/line. Perhaps you have a garage or barn several hundered feet out and you want to switch something on or off (without using radio signal, or dangerous and costly 120V or higher lines).
I looked on Google for some links to easy USB interfacing. Most computers have USB now. This site has a good discusstion:
http://www.beyondlogic.org/usb/usbhard.htm
And this one looks like the simplest for experimentation and actuall use:
http://www.usbmicro.com/
Duration : 0:3:13
[youtube VsM356CNDbc]
May 18th, 2010 at 2:21 pm
You sound like …
You sound like Jigsaw from the Saw movies. 5 stars!!
May 18th, 2010 at 2:21 pm
Exelente !
Exelente !
May 18th, 2010 at 2:21 pm
I can take a guess …
I can take a guess. The photosensor would have to be an infra-red photosensor, and then probably have to amplify that signal on the photosensor and send it to the optocoupler still with the current necessary for it to turn on the high voltage side of it that will turn on the triac. I guess using a remote control would eliminate the need for a “laser and sensor” and it would probably be very sensitive too like a tv sensor in a room, but they might have problems if placed in the same room then.
May 18th, 2010 at 2:21 pm
How would one use …
How would one use this circuit with a universal remote control as a switch to the triac? I guess you would need a photo sensor but what else?
May 18th, 2010 at 2:21 pm
Plus another thing …
Plus another thing important is that SCR when switched to the ON or in it’s conducting mode will stay on unless current is stopped flowing between the main “power” or current terminals.
May 18th, 2010 at 2:21 pm
In the video text …
In the video text is an example in another video someone has made. Basically I think an SCR (silcon controlled rectifier) is a transistor-like solid state switch for high DC current. A TRIAC is very similar to a SCR but is used for AC current switching….and some might say that a TRIAC is equivalent to two scr’s connected to allow AC. I think “dimmer” type power applications also use SCR’s and TRIAC’s. I’ll try to post a circuit diagram today or tomorrow of the one shown in this video.
May 18th, 2010 at 2:21 pm
Thanks for sharing …
Thanks for sharing that! Could you provide a circuit diagram? Another question that comes to mind is what is the difference between a triac and an scr?