3 core 6 way circuit

Discussion in 'General Electronics Chat' started by samsam311, Mar 21, 2013.

  1. samsam311

    Thread Starter New Member

    Mar 21, 2013
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    Hello,

    I am fairly new to the electronics game and by no means am i professional so please forgive my lack of know how when it come to more complicated devices.

    I have set out to build a circuit that can light 6 different lamps individually down three cores of cable . I have done this by flipping the polarity of each combination of 2 cores (thus 2 polarities x 3 cores is = 6 possible combinations) and using diodes to prevent more lamps lighting.

    If i was using only 4 lamps there would be no need for anything other than diodes but as soon as we introduce the last two lamps to the circuit there is a problem.

    They need to be isolated during lamp 1-4 configuration and then for lamp 5-6 config lamps 1-4 need to be isolated. I had thought about doing this by using a transistor to isolate 5-6 and then JFET's to isolate 1-4 .

    yet we must remember that only 3 cores can run into this set up from the power supply, leaving only 1 spare (changing) core to trigger the JFET's and transistor gates , and they must not effect the operation of the other 4 configurations.

    Attached is a picture of the diagram i have made. I have shown the planned positions of where a break / make of the circuit must be temporarily made. Although this must be done only with the remaining spare core at the time of lamp 5-6 which happens to be core 2 . although these cannot block the current when it is needed in configuration 1-4.

    I'm sorry that's a bit of a crazy idea. All i am using the transistor and JFETS for is as switches, but i remain unsure as to how i might connect them so as not to disrupt the other configurations when needed.

    Thank you !

    Sam

    DIAGRAM [​IMG]
     
  2. antonv

    Member

    Nov 27, 2012
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    Sorry, can't open your diagram. What kind of lamps are you using and how much current do they need?
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    What you are doing is called "charlieplexing" (after one of the first guys to do this.Do goggle that term.

    I just did and found this neat picture:

    [​IMG]

    Forget the uC and the resistors, it shows 3 lines driving 6 lamps with diodes. (note lamps are not shows but work the same way).
     
    Last edited: Mar 22, 2013
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  4. richard.cs

    Member

    Mar 3, 2012
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    Charlieplexing will allow you the 6 lamps from 3 wires, if you're using filiment lamps rather than LEDs you may find some lamps light unintentionally. Consider the circuit ErnieM posted, if you wanted to light L2 you would drive Port1 high, Port2 to ground, and leave Port3 unconnected. L2 clearly lights but there is also a path via L6 and L3. With the LEDs there is a voltage below which no conduction occurs, the combined forward voltage of L3 and L6 exceeds the supply voltage so they don't light. If these were filament lamps though, or LEDs driven from a higher voltage, then L3 and L6 would light dimly when L2 was lit.

    Another way of doing this would be to dedicate two of the wires as power and send serial data down the third. A shift register or a microcontroller at the far end would decode this and control an arbitarily large number of lamps.
     
  5. samsam311

    Thread Starter New Member

    Mar 21, 2013
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    Ok, Thanks very much for the help.

    as soon as we get out of the realms of analogue my knowledge becomes limited, so please forgive me for asking so many questions.

    I think i will try to build a simple 6 way 3 core using the charlie-plex method. I've been researching what sort of parts i would need but i'm really not sure.

    Could someone give me a list of components i would need to control the circuit , i have all the led end sorted ive got my six lamps and diodes but no idea of what to get in the way of a micro control to set up the High/Low/Input change , and how to control these changes.

    Thanks again , this has been extremely helpful
     
  6. samsam311

    Thread Starter New Member

    Mar 21, 2013
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    But wait , will current not still flow even when i theoretically 'disconnect' the spare core. Say i wanted to put the middle core to input and light L6 would current not still flow straight through L2 L4 back to the low core ? as well as L6.

    or does the input mode effectively break the connection, not just to the controller, but between L2 and L4
     
  7. richard.cs

    Member

    Mar 3, 2012
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    If you use green LEDs for example, which have a forward voltage of around 2.4 V, and use a 5V supply then the voltage across L6 will be 2.4 Volts (with the rest dropped accross the resistors), But for current to flow through L2 and L4 you would need 2*2.4 = 4.8 Volts.

    Essentisally L6 clamps the voltage to the point where L2 and L4 cannot conduct. This should always work if all your LEDs are similar in forward voltage, but if L6 was blue (Maybe 4 Volts forward drop), and L2 and L4 were both red (2 Volts forward drop) then you might have problems.

    For testing you could use three single-pole double-through centre-off switches rather than a microcontroller.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    One thing you will have to muddle thru is getting 8 more posts here so you can post pictures. (Off-Topic posts don't count for this) New friends have to pass this small test to see if they are really dedicated.

    What lamps do you want to use? That is going to determine what you need to drive them.

    Here are my thoughts on starting with Microchip PIC microcontrollers.
     
  9. samsam311

    Thread Starter New Member

    Mar 21, 2013
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    Richard.cs,

    So if my 6 devices are all of identical parameters there would be no chance of leak onto other devices providing i had a resistive load over each device?

    Also , i am not designing the circuit for led's , i will be using devices that behave like flash lamps, they have a resistance of 1.5ohm and require .5 amps
     
    Last edited: Mar 22, 2013
  10. richard.cs

    Member

    Mar 3, 2012
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    This form of multiplexing only works well when the lamps used are fully off at no less than half the voltage they are fully on. For example a red LED might be fully off at 1.9 Volts and fully on at 2.3 Volts.

    With filament lamps this doesn't really work, a lamp might be fully on at 6 Volts, but still visibly glowing at 3 volts - the end result is that 1 lamp lights properly and two don't light at all. Flashing lamps compound the problem further by varying the load.

    The only way I can see of making it work with filament lamps is by adding zener diodes. Consider each lamp having a normal diode and a zener diode (opposite to the normal diode) in series with it. If your lamps need 3 Volts then use 6 Volt zeners and run from a 9 Volt supply. (scale for other lamp voltages). Don't bother with R1, R2, R3 as they are not needed with filament lamps. The downside here is the efficiency - you loose 2/3 of the power in the zeners.
     
  11. richard.cs

    Member

    Mar 3, 2012
    162
    31
    I've attached a schematic of what I was describing for filament lamps.

    filament charlieplex.gif
     
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