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Thread: Multiple Button w/ Resistors

  1. #41
    Variable Bitrate
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    I'm affraid I'm not really following. All I know is both "active high" or "active low" both seem to work for me, except both buttons are dropping/upping the voltage to the same value.

  2. #42
    Maximum Bitrate Mickz's Avatar
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    Quote Originally Posted by SKiTLz View Post
    I'm affraid I'm not really following. All I know is both "active high" or "active low" both seem to work for me, except both buttons are dropping/upping the voltage to the same value.

    Measure the voltage across the 10k resistor what is hard about that?

    The top of the 10k should go to the input connection the FB, the bottom of the 10k should go to a ground connection on the FB.

    Active high and active and low are meaningless without reference.
    Active High means that when an event occurs the output will be high IE +5v.
    Active Low means that when an event occurs the output will be low IE 0v.

    It usually applies to Digital outputs / inputs.

    The signal you are reading is an analogue signal – it can have any value (between 0 and 5v in this case) not just high or low, 5v or 0v.

    The ADC (analogue to digital convertor) of a Micro does not care about anything except the voltage at its input with reference to ground. That voltage is the voltage developed across the 10k resistor.

    Unless the FB ADC inputs have been modified from the norm, it should be the same.
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  3. #43
    Variable Bitrate
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    I appreciate the help. I just don't exactly understand the theory behind everything so bare with me.

    Ok so I measured across the 10k resistor (INPUT->GND) and it is 3.19V unpressed and 4.78V pressed. So exactly what I said, I was measuring it correctly. But again, it is 4.78V pressed for BOTH buttons.

  4. #44
    Maximum Bitrate Mickz's Avatar
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    Quote Originally Posted by SKiTLz View Post
    That 4.6 is supposed to read 4.7. Typo.
    No problems – I understand, we have all been there and started there. However trying to fault find when you can’t see or touch the equipment is not easy so excuse the repetitive questions.

    If you look at your circuit there are two buttons. With both buttons off (un-pressed) AND no connection to the FB there HAS to be 0 volts across the 100k (now a 10k for our test)

    Once that has been established, connect it to the FB, there should be 0 volts across the 10k under the same condition (no button pressed), is this the case?

    You said “But again, it is 4.78V pressed for BOTH buttons.”

    If this is the case without it connected to the FB then you either have:

    A: The circuit is wired up differently then shown.
    B: The +5 volt supply is dropping when you press a button.
    C: The resistor values are not what they indicate.
    D: You have a faulty lead or connection.
    E: You have discovered a new unheard of electrical principle
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  5. #45
    Raw Wave
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    Not that I understand why the 100R resistor is there (I haven't read the thread thru) but take it out - you aren't measuring a 0.1% voltage change.
    Else make it substantial - 10k or more.

    (I've forgotten the analog impedance of the FB....)

  6. #46
    Maximum Bitrate Mickz's Avatar
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    You are correct of course, however for the purpose of identifying the current problem, I was trying not to confuse the situation by changing to many things at once.

    I believe the FB is switching a number of inputs to one ADC port. One of the problems with a low resistance into the ADC port is the accuracy loss caused by the inability of the ADC conversion CAP to fully charge during the allocated sampling period. From memory around 1.5 to 3k is the recommended minimum load resistance for the Microchip ADC ports running at low speeds.

    At the moment we are trying to get a correct voltage reading without any connection to the FB Micro.
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  7. #47
    Fusion Brain Creator 2k1Toaster's Avatar
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    The input impedance should be kept below 2.5Kohms for the ports. It is a single ADC, but the time it samples for is extremely long. I think a picture of the setup is in order. It definately sounds like something is very wrong with the wiring.
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  8. #48
    Variable Bitrate
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    Finally had some more time to play...

    Mickz I took your advice.. I have everything connected exactly as show. If I measure the voltage across the 10k (probe on either side) I'm getting 3.2V, and you are saying I should be getting nothing. So what gives. Is it possible my buttons are passing the voltage and work on some kind of resistance instead?

    I know you guys probably think I've got something hooked up wrong but it's honestly exactly as I diagramed.

    Also If I measure voltage across the button (while connected to the FB) I get 1.18V. So clearly voltage is passing. Why it is lower at the button that I see at the brain is beyond me though.

    ---------- Post added at 11:05 PM ---------- Previous post was at 10:40 PM ----------

    I can put the findings up.. Hopefully you guys can interupt them as to what it means..

    I just put my multimeter inline on the 5V line. So intead of +5V PIN -> Switches it is +5V Pin -> MM lead -> MM lead -> buttons..

    Now the FB is reading 0V like your saying it shoud.. Well very close.. It's getting a 0.0.... reading still.

    What the hell. Having my multimeter inline on DCV 20 shouldn't change anything to my knowledge.
    Last edited by SKiTLz; 03-10-2011 at 10:44 PM.

  9. #49
    Maximum Bitrate Mickz's Avatar
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    Having the multimeter in line is the same as putting a large resistor in line. The voltage will drop.

    It’s lower with the FB connected because of the impedance of the FB.

    You need to disconnect each switch from the circuit. One of them is leaking or they are not simple on/off switches.

    They don’t have an inbuilt LED by any chance?
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  10. #50
    Variable Bitrate
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    Since I have everything connected EXACTLY as you guys are saying, same resistor values etc etc, the only variable is the actual buttons themselves. I've attached some pics as close up as I could get (need a macro lense). Maybe something jumps out at you cause I'm seriously lost why this still isn't working. The more reading I do the more I'm convinced everything is correct.



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