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on/off switch based on scart pin 8

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    on/off switch based on scart pin 8

    I have the need to monitor whether two tv media devices are on or off. I've decided that the easiest/cheapest solution would be to use pin 8 of the scart lead which is 0-0.4V when off, 5-8V for 16:9 display and 9.5-12V for 4:3 display. I need to create either a on (voltage above 5v) or off(voltage is 0V) solution which I can connect up to the Joystick plugin, which would effectively complete/break the connection on one of the buttons. I'm thinking that this could be done with either a transistor or relay but I'm not sure on the best way or components to use for this.

    I'm pretty good with a soldering iron if someone has the know how to advise on a small circuit that I could construct to get a on/off switch based on output from pin 8 on scart lead.

    Thanks
    Simon

    #2
    Hi

    Thats a novel approach... well done!

    I would suggest a low power relay, just to retain total isolation of all circuits....

    There are some low power DIl packaged relays always on ebay for not much money.

    David
    ---------------------------------------------------http://weather.penicuik.org

    Comment


      #3
      Originally posted by djblack View Post
      Hi

      Thats a novel approach... well done!

      I would suggest a low power relay, just to retain total isolation of all circuits....

      There are some low power DIl packaged relays always on ebay for not much money.

      David
      Thanks, I thought it was quite unique hadn't heard of anyone doing it before !

      I've got Maplins 1/2 mile a way so I'll probably take a look at their website later and see what I can get that will do the job.

      Comment


        #4
        I was looking to do something similar by auto switching my SCART inputs whenever a PIR was triggered to switch a CCTV camera...I decided not to in the end as it would probably drive me crazy.

        If you are trying to detect between 5 and 12v I would look at a relay, max coil voltage as 12v...problem is you might struggle to find a relay coil that will still trigger the contacts at 5v.

        Or you could build a small transistor circuit with an NPN transistor, as long as the collector-base voltage is above 12v, something like a 2N2222?...or an opto isolator?

        Comment


          #5
          If it was me, I'd use an opto isolator.

          Total isolation, low current ,you don't have to worry about sticking a diode over the coil, and you could use the current limiting resistor to trigger it at whatever voltage you want.

          Just a suggestion....

          Comment


            #6
            Originally posted by TechnoJunkie View Post
            If it was me, I'd use an opto isolator.

            Total isolation, low current ,you don't have to worry about sticking a diode over the coil, and you could use the current limiting resistor to trigger it at whatever voltage you want.

            Just a suggestion....
            Sorry for the delay in responding been stuck doing other stuff !

            Opto isolator with current limiting resistor sounds like what I need.
            I need to trigger it for anything above 5 volts.

            Bit of a cheeky question but any chance you could take alook at the maplins website for me and advise what parts I would need ?

            Thanks
            Simon

            Comment


              #7
              Originally posted by Simonk View Post
              Sorry for the delay in responding been stuck doing other stuff !

              Opto isolator with current limiting resistor sounds like what I need.
              I need to trigger it for anything above 5 volts.

              Bit of a cheeky question but any chance you could take alook at the maplins website for me and advise what parts I would need ?

              Thanks
              Simon

              I've just PM'ed you.

              Comment


                #8
                TechnoJunkie,

                Thanks for all your help with providing parts and instructions.
                I've now set up a test with a cable running through the house to the media box and it all works fine.

                I'm now looking to incorporate this into the spare 4 wires in the cat5 cable so that I don't have to run more cables, potentially 3 switches could be run through these spare wires. Is 5 volts on a pair of cat5 cables likely to affect the reliability of the actual network running on that cable ?

                Comment


                  #9
                  Originally posted by Simonk View Post
                  TechnoJunkie,

                  Thanks for all your help with providing parts and instructions.
                  I've now set up a test with a cable running through the house to the media box and it all works fine.

                  I'm now looking to incorporate this into the spare 4 wires in the cat5 cable so that I don't have to run more cables, potentially 3 switches could be run through these spare wires. Is 5 volts on a pair of cat5 cables likely to affect the reliability of the actual network running on that cable ?

                  Simon

                  Thanks for the thanks and I'm glad to see it's working fine.

                  And no, 5v on the other pairs shouldn't effect the data pairs.


                  Cheers

                  Andy

                  Comment


                    #10
                    I'm now looking at connecting my Combi boiler up to HomeSeer so that I can monitor the status of whether the burner is on and whether it is heating the house or hot water and finally if there is an problem and it has been locked out. It seems that the easiest way of doing this would be linking up to the existing leds on the control panel. So I have conected a wire to either side of each LED and if I stick my meter on the other end of the cables when the LED is on I get 1.68V DC which I beleive is too low for the opto isolators I am currently using. The other thing that slightly concerns me is that I accidently touched on one set of the cables and I got a bit of a tingle, nothing major just enough to make me pull back off it. This cable still measures 1.68v when metered but does this mean that this just probably has a higher current going through it ?

                    What would be the best way to connect these connections to the joystick pad ? Are there optoisolators that work at this voltage ?

                    Thanks
                    Simon

                    Comment


                      #11
                      Simon,

                      Be very careful here. These types of board are not isolated from the mains and just drop the supply through resistors/regulators to get the required voltages. If you touch some parts you will get a nasty shock.

                      If you wish to continue down this route you MUST use opto-isolators to connect to the LED's.

                      Look at the board and you will (should) see that each LED will have a series resistor. You need to make your connection on the side of the resistor not connected to the LED and the other LED connection not connected to the resistor. Your opto LED MUST then be connected through a new series resistor of similar value to that on the board from these two connections.

                      Make sure your Opto is high voltage rated (such as a 4N25) and make sure all connections are sleeved.
                      Jon

                      Comment


                        #12
                        I've finally got around to taking a look for the resistors you mention but there doesn't appear to be any.

                        I've decided to change my approach to this and thought that I could actually do this without physically connecting to the board by using a (I cannot remember what it is called ! Is it a photo resistor or photo diode ) fixed on the front panel infront of the LED connected to the cable going to the joystick connections. Then if the LED turns on the thing detects this and completes the circuit.

                        Can you advise what I would need, is it a photo resistor or photo diode ? How do I know how much light they trigger at as to what I need ?

                        Thanks
                        Simon

                        Originally posted by jon00 View Post
                        Simon,

                        Be very careful here. These types of board are not isolated from the mains and just drop the supply through resistors/regulators to get the required voltages. If you touch some parts you will get a nasty shock.

                        If you wish to continue down this route you MUST use opto-isolators to connect to the LED's.

                        Look at the board and you will (should) see that each LED will have a series resistor. You need to make your connection on the side of the resistor not connected to the LED and the other LED connection not connected to the resistor. Your opto LED MUST then be connected through a new series resistor of similar value to that on the board from these two connections.

                        Make sure your Opto is high voltage rated (such as a 4N25) and make sure all connections are sleeved.

                        Comment


                          #13
                          As you do not state the colour of your LED's its probably best to go for a photo-transistor which is suitable for all colours.

                          Look at the SHF300-3 which should do the job nicely.
                          Jon

                          Comment


                            #14
                            Originally posted by jon00 View Post
                            As you do not state the colour of your LED's its probably best to go for a photo-transistor which is suitable for all colours.

                            Look at the SHF300-3 which should do the job nicely.
                            I've just been to my local Maplin store and they are out of stock ! Just ordered some online for delivery.

                            Thanks for your help.

                            Comment


                              #15
                              Originally posted by jon00 View Post
                              As you do not state the colour of your LED's its probably best to go for a photo-transistor which is suitable for all colours.

                              Look at the SHF300-3 which should do the job nicely.

                              I've got the above phototransistors and connected to the joypad but the phototransistor doesn't seem sensitive enough and only triggers when it it right up against a really bright light. I actually had to put it up to the light in the room to get it to trigger !
                              Is there any way to get it to trigger with less light ?

                              Comment

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