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  • Neon/Fans/Anything controlled from your PC

    Probably old news with the Fusion Brain now released - but this is cheap!!


    Too much research and a few hours thinking turned into this:








    small demo vid



    I'm trying to think of all the useless possibilities for this. Will be posting my source code and schematic some time in the future.

  • #2
    Why use a realy for this?
    Why not just use a MOSFET transistor instead?

    Comment


    • #3
      I have no experience in using them. However from reading up they are simply transistors which accept very low current.

      Are there any reasons why I shouldn't use them? What about isolation of the parallel port?

      Comment


      • #4
        You might want to look at using a Opto-isolator in the circuit and this will allow you then to use a mosfet.

        A opto is more or less a LED with a receiver, So by turning on the LED you are completing the circuit on the other side of the chip where the receiver is and this will allow you to switch a logic circuit while making sure its not connected to your delicate circuit.

        A common use for these chips are in computer PSU as most will have them.

        To me they are the best source of isolation, But have a look and see what you think.
        2004 Holden WL Caprice Auto GENIII
        Base System = Raspberry Pi
        Everything else is pending for now as switched from a Mini-ITX setup

        Comment


        • #5
          .. and if your circuit doesn't use much current you don't even need a Mosfet connected to the isolator, just drive it directly

          Comment


          • #6
            You will want to isolate it due to if there is a fault with the mosfet or a surge, It can short back into the parallel port. Using the isolate method, The most you will do is blow the opto.
            2004 Holden WL Caprice Auto GENIII
            Base System = Raspberry Pi
            Everything else is pending for now as switched from a Mini-ITX setup

            Comment


            • #7
              Ooh, maybe I should have said. I have two concepts - the other one does involve the opto-isolator. I just need to put it all together.

              Any recommended part numbers for the MOSFET? I normally use 2N2222A transistors. Saving on components would be nice.

              Comment


              • #8
                Here a few projects that are used for xmas lights: This is a common project
                SSR = Solid State Relay

                Project One:christmaslights.netbootdisk.com SSR
                Two: dv-fansler.com SSR
                Three: www.ksochristmaslights.com SSR
                Four: computerchristmas.com Channel Multiplier Style

                I cant remember what mosfet we ended up using when building the xmas lights controller, But the overall setup was running on 24v. The mosfets did not need any heat sinks so i think their rating would have been 48/120v or something.

                Have a google around on "Xmas Light controller mosfet", I jsut cant atm as my broadband has been throttled down due to a house mate who has no respect at all....
                2004 Holden WL Caprice Auto GENIII
                Base System = Raspberry Pi
                Everything else is pending for now as switched from a Mini-ITX setup

                Comment


                • #9
                  Originally posted by mayhembdm666 View Post
                  You will want to isolate it due to if there is a fault with the mosfet or a surge, It can short back into the parallel port. Using the isolate method, The most you will do is blow the opto.
                  Just put a resistor in between the PC and the gate of the MOSFET, then you wont destroy your PC if the MOSFET shortcircuits.

                  Comment


                  • #10
                    A resistor can short...So this is still unsafe.

                    For proper protection, You need to have a safe gap for the circuit..
                    2004 Holden WL Caprice Auto GENIII
                    Base System = Raspberry Pi
                    Everything else is pending for now as switched from a Mini-ITX setup

                    Comment


                    • #11
                      Originally posted by Andrew_C View Post
                      I have no experience in using them. However from reading up they are simply transistors which accept very low current.
                      Then you don't read up the right places.
                      You can get power MOSFETS that can handle very high load currents. They are used in most switched mode power supplies (SMPS) like all PC power supplies and here they handle very high currents. In SMPS the MOSFETs switch at high frequencies and here a high percentage of the power dissipated in the MOSFET is actually not dissipated during on mode, but in while switicng between on- and off modes.
                      But if you just use it instead of a realy and not for a PWM circiut, then then you don't have to worry much about swithing losses, here you dissipate all the power in on mode.



                      QUOTE=Andrew_C;1288360]Any recommended part numbers for the MOSFET? I normally use 2N2222A transistors. Saving on components would be nice.[/QUOTE]
                      You should look for N-channel power MOSFETS. The lower RDS(on) (resistance from drain to source in on mode) the higher current the MOSFET will be able to handle - and the larger and more expensive it will probably also be. The good thing is that MOSFETs for car applications only have to handle 12V, so instead of picking a MOSFET that can handle high volatages, pick one that has low RDS(on) instead.
                      When you know the RDS(on) and the current you load is going to draw you can easily calculate how much power is dissipated in the MOSFET while it on.
                      Let's say you have a 1 Ampere load and a MOFET with an RDS(on) of 0.1 ohm.

                      You can for example look for a suitable N-channel power MOSFET here: https://ec.irf.com/v6/en/US/adirect/...N=0+4294841672
                      International Rectifier is one of the biggest manufacturers of power MOSFETs.
                      But try to check which N-channel power MOFETs your preferred electronic componets store sell and pick one of these.

                      It's also important to chose a MOSFET with low enough Gate-Soruce threshold voltage for your input signal to be able to turn it on.
                      The Gate input impedance is virtually so high that you draw zero current from your input signal. This also means MOSFETs are very sensitive damage from static electricity, especially before you have monutented it in the circuit.

                      When switching inductive loads like fans, remember to ad a flywheel diode to protect the MOSFET from back-EMF.

                      Read this tutorial:
                      The MOSFET as a Switch
                      http://www.electronics-tutorials.ws/...or/tran_7.html


                      If you want to use an opto-isolator you can get MOSFETs circuits with build in opto-isolator that can handle both a.c. and d.c. loads. There are also know as photovoltaic relays: https://ec.irf.com/v6/en/US/adirect/...N=0+4294841620
                      IR has a photovoltaic relay that can handle continuous load currents up to 6 Ampere DC, packed in a small 6-pin DIP package: https://ec.irf.com/v6/en/US/adirect/...ame=PVN012APBF

                      Comment


                      • #12
                        Originally posted by mayhembdm666 View Post
                        A resistor can short...So this is still unsafe.

                        For proper protection, You need to have a safe gap for the circuit..
                        Resistors hardly ever short circuits, their failure mode is usually open circuit.
                        But the resistor in front of an opto isolator is just as likely to short circuit as a resitor in front of a MOSFET, so you are not anymore protected from a short circuited resistor if you use an opto isolator as if you use a MOSFET.
                        I used to repair electronic devices for a living for several years and short circuited resitors is a not issue at all really - in reality it hardly ever happens, I can't rember seeing short circuited resistors. Wirewound resistors are maybe more prone to this, but they are not used here, but only for some power applications.

                        An opto-isoltated circuit does however offer more protection, it can protect from reverse voltage and large over voltages. But you don't need an opto isolator to simply protect from a short circuited load transistor. The opto-isolator could short circuit the inputs pins too and draw a lot of current. But a resitors in fron of the opto-isolator or load transistor could prevent overloading the output port in case of a short circuit.

                        If you want opto-isolation and MOSFET you can use a Photo Voltaic Relay as suggested in my earlier post. This is a good and small solution and I think the price is about the same as a regular realy, while it's much smaller and doesn't need a transistor to drive it if your output can supply enough current for the LED in the Photo Voltaic Relay, and you don't get the clicking noise of regular relays.

                        Comment


                        • #13
                          Its not a common fault, But can and does happen.
                          The opto is used to create safe zone that can not be shorted regardless.

                          If by chance u do ever have a resistor short then the next part inline gets the full voltage, Having the emitter on the opto fail simply means it will not pass that point in either case
                          2004 Holden WL Caprice Auto GENIII
                          Base System = Raspberry Pi
                          Everything else is pending for now as switched from a Mini-ITX setup

                          Comment


                          • #14
                            Ah, sorry I came across wrong. I know they can handle high load currents. I was referring to the switch current required being low - hence the sensitivity.

                            I have to say you definitely know your stuff in this area and thanks a lot for your input. I am interested in the Photo Voltaic relay but I can't find a good source of them in the UK.

                            I don't want to over-complicate this project. I wont be drawing any more than 2A I shouldn't think (which is what my relay is rated at). Mainly will be controlling automotive relays - I think their coils are around the 200 milliamps.

                            The simplest circuit design so far with the least cost involved is the MOSFET + resistor.

                            My main source of components for small projects is Maplin.co.uk as they have a store very close by to me.

                            >>>>>>>>>>>>>>
                            http://www.maplin.co.uk/Search.aspx?...SFET&source=15
                            >>>>>>>>>>>>>>

                            Is my selection limited so much as that none of them would work?

                            Comment


                            • #15
                              Originally posted by Andrew_C View Post
                              Ah, sorry I came across wrong. I know they can handle high load currents. I was referring to the switch current required being low - hence the sensitivity.

                              I have to say you definitely know your stuff in this area and thanks a lot for your input. I am interested in the Photo Voltaic relay but I can't find a good source of them in the UK.

                              I don't want to over-complicate this project. I wont be drawing any more than 2A I shouldn't think (which is what my relay is rated at). Mainly will be controlling automotive relays - I think their coils are around the 200 milliamps.

                              The simplest circuit design so far with the least cost involved is the MOSFET + resistor.

                              My main source of components for small projects is Maplin.co.uk as they have a store very close by to me.

                              >>>>>>>>>>>>>>
                              http://www.maplin.co.uk/Search.aspx?...SFET&source=15
                              >>>>>>>>>>>>>>

                              Is my selection limited so much as that none of them would work?

                              If you only need to drive automotive relays, use a ULN2003 (16-pin package) Its cheap, has built in flyback diodes and has 7 drivers in them. If you need 8 since I suppose your using a parallel port, use the ULN2803

                              P.S. you are using a parallel port right.

                              -dave

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