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Advice please on design not working as expected

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9件のコメント

  • James Head

    The anode should be connected to a more positive potential than the cathode. Normally, this means the anode connected to positive power, and the cathodes connected to 0V or ground, with the appropriate limiting resistors in there somewhere.

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  • Jennifer Smith

    Hi James,

    So are you saying that the JST connectors are correct and that they should have pin 3 to ground?  

    The cathodes go through resistors but they are on signal tracks to go to the switch.  They, I assume are connected to ground through the switch?

    On the secondary connected board the standard LEDs (not bi-colour) don't work unless they are reversed, ie LED cathode to 5v, LED anode to gnd so something is wrong through the connector.  

     

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  • Brad Levy

    Is the circuitry shown the same (or intended to be the same) on both boards?

    If so, then the way I interpret the circuit, a toggle switch plugged into either board could turn on one color or the other of LED on each board that has power applied. The JST cable between the boards would provide a common ground between the two boards, allowing the toggle switch to ground the white or red LED cathodes of all connected boards. But if power is only applied to one of the two boards, the LEDs on the other board will remain dark, because there is no path for the positive supply to make its way from the powered board to the unpowered board.

    I would check the polarity of your battery or supply wiring on the board with the single-color LEDs. With that board by itself, and battery installed or power connector plugged in, and toggle set to ground the relevant LED, is the voltage on what you think should be the anode line of the LED positive or negative with respect to ground? If it is negative, you have your battery or supply connector reversed.

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  • Jennifer Smith

    Thanks Brad,

    We're sure it's not the battery.  As it stands, power is flowing to the other board, this we have tested and have checked the voltages - it's flowing to the LEDs, but via the cathodes.  

    It has to be the connectors because the boards both work individually as they should so it has to be the connection between the two.

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  • Brad Levy

    Don't forget to inspect the cable, too. It could have pins swapped.

    You might try removing power and batteries, then connecting the two boards, and checking with a meter for continuity (and non continuity) match expectations between the different points connected on the two boards by the cable.

     

     

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  • Brad Levy

    On the non-bicolor LEDs, do they appear to function with normal polarity when the two boards are not connected?
    You might also double-check those (non-bicolor) LEDs out-of-circuit with a meter on the diode setting, + (red) to anode, - (black) to cathode. Most meters will supply enough voltage/current to light the LED in that setting, though it may be quite dim.

    Then swap the leads and you should see no illumination.  Just suggesting this in case you got a batch of mis-packaged LEDs.

    (It is hard to troubleshoot from afar with only partial information, and when it isn't always clear the circumstances under which some of the reported behavior is taking place.)

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  • Jennifer Smith

    Hi Brad,

    Yes, they work fine when the boards are not connected.  We've looked at it again and we're pretty sure that the problem is that the pin 3 on the connectors should be to positive not negative.  The LEDs are going to negative so if you plot it out like a parallel circuit it makes sense that they have to go to positive, otherwise there's no path for the current.  

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  • Brad Levy

    If the second board plugs into J5 or J6, and it is intended that the LEDs on the second board turn on when selected (grounded) by the toggle switch plugged into the first board, while getting power from the first board, then you would need to connect pin 3 of J5 and J6 to the positive supply on the main board, and to the anode(s) of the LEDs on the second board.

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  • Jennifer Smith

    Hi Brad,

    Yes, that's what we were thinking.  Thanks for confirming our thoughts.  I did get a friend to check the original schematic but somewhere along the line things must have got confused and the error was made.

    It's difficult when you get close to the design to spot the obvious sometimes!

    Thanks again.  

     

     

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