using GetADC to measure resistance

Started by flashsanchez January 17, 2005

I hooked up a potentiometer fine to my BX-24 and I have that running
fine but now I am having problems trying to measure the resistance of
a Cds. I guess this is more of a shortcoming of my knowledge of
electronics but how exactly does the GetADC function work? The
potentiometer has 3 different inputs but how would i just measure the
resistance of just a regular resistor? Any help would be greatly
appreciated.




The BX-24 doesn't actually measure resistance, but it does measure voltage and time.

Initially, you used the potentiometer as a voltage divider. One side to +5, the opposite side to ground. The third leg changed voltage as you adjusted the pot.

For example: As you turned the pot, the resistance between the leg (attached to BX24) and the voltage supply decreased while the resistance between the leg and ground increased. The sum of both resistors would remain constant - that depend on your pot. Of course it works the other way when you turn the pot the opposite direction.

It works similar with a CdS, except you provide the other resistor. It remains constant while you CdS varys with different light. Measure the resistance with the CdS in light and dark to get an average resistance. Try a resistor in that range and use the ADC to check the voltage that is seen at the junction between the two.

Hope that helps,
Thad

flashsanchez <> wrote:

I hooked up a potentiometer fine to my BX-24 and I have that running
fine but now I am having problems trying to measure the resistance of
a Cds. I guess this is more of a shortcoming of my knowledge of
electronics but how exactly does the GetADC function work? The
potentiometer has 3 different inputs but how would i just measure the
resistance of just a regular resistor? Any help would be greatly
appreciated. ---------------------------------
Yahoo! Groups Links

To
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Wow, thanks. That was extremely helpful and informative. Thank you
for your help.

--- In , Thad Larson <highwayman_33402@y...> wrote:
> The BX-24 doesn't actually measure resistance, but it does measure
voltage and time.
>
> Initially, you used the potentiometer as a voltage divider. One
side to +5, the opposite side to ground. The third leg changed
voltage as you adjusted the pot.
>
> For example: As you turned the pot, the resistance between the leg
(attached to BX24) and the voltage supply decreased while the
resistance between the leg and ground increased. The sum of both
resistors would remain constant - that depend on your pot. Of course
it works the other way when you turn the pot the opposite direction.
>
> It works similar with a CdS, except you provide the other resistor.
It remains constant while you CdS varys with different light.
Measure the resistance with the CdS in light and dark to get an
average resistance. Try a resistor in that range and use the ADC to
check the voltage that is seen at the junction between the two.
>
> Hope that helps,
> Thad
>
> flashsanchez <jsanchez@y...> wrote:
>
> I hooked up a potentiometer fine to my BX-24 and I have that running
> fine but now I am having problems trying to measure the resistance of
> a Cds. I guess this is more of a shortcoming of my knowledge of
> electronics but how exactly does the GetADC function work? The
> potentiometer has 3 different inputs but how would i just measure the
> resistance of just a regular resistor? Any help would be greatly
> appreciated. > ---------------------------------
> Yahoo! Groups Links
>
> To >
> ---------------------------------
>