Analog input value

[fanfanfan99]

I made my own wearable flexible sensor (flexible resistor) but I connected a 10k （1M）resistor and 5v and wanted to take a reading of the resistance of this resistor but the arduino analog inputs are like floating pins but the connection is correct

does anyone fix this problem before？

[LarryD]

• Always show us a good schematic of your proposed circuit.
  Show us good images of your ‘actual’ wiring.
  Give links to components.

[fanfanfan99]

sorry it was my first question，there are coding and circuit.

[gilshultz]

Hint: The A/D works best with an input impedance of 10K or less. If you must use a higher resistance, you should add a capacitor to the input pin of the A/D for better performance.

[fanfanfan99]

i saw this hint in other's problem, so i change res from 1m to 10k.shall i add a capacitor after i have already changed the res?

[build_1971]

Do you have 2 homemade resistors?
The values in your printout move together. Which makes me think your vcc is not stable.
How do you power your setup?
What else is connected?

[fanfanfan99]

my power（5v） came from arduino，i use a expand board with uno r3.

but several weeks ago，they were working well.

[build_1971]

This setup will pick up emi.
Keep wires to and from sensors together.
Add a 100 nF cap near your analog input.

[fanfanfan99]

@build_1971

This setup will pick up emi.
Keep wires to and from sensors together.
Add a 100 nF cap near your analog input

put a 100nf cap between analog input and gnd?

[johnerrington]

Hi @gilshultz, I'm trying to dispel that "10k" nonsense.

Here is the input to the ADC

I dont know if you have seen the results of my tests with a 500M resistor that show the "10k" is only relevant if you are measuring signals that change VERY fast.

and the results of my test with a step wave. The x axis is 1 unit = 20 usec.
The Y axis is raw ADC value (the step wave from the D6 output is attenuated so the max ADC reading is a bit less than 1024)

of course on a breadboard with a 500M resistor and unscreened its subject to interference.

I'd suspect the resistors, the connections or (since we havent been shown it) the code.

[gilshultz]

The cap will probably help stabilize the reading.

[JohnLincoln]

@johnerrington

I'm trying to dispel that "10k" nonsense.

I'm on your side John.

I frequently use a 1MΩ resistor from an analogue input to GND, so that I can use it with a X10 oscilloscope probe.
It works well.

[jim-p]

@fanfanfan99

but several weeks ago，they were working well.

Maybe that white goop in the plastic bag has dried out.

[build_1971]

Yep, between analog input and gnd.

[build_1971]

To be honest, I do not understand this whole issue about resistors if 10k or 500M. The resistor should be around the same value as the 'sensor' resistor...

[fanfanfan99]

@jim-p

Maybe that white goop in the plastic bag has dried out.

hi my own res can change from several k to several m ohms，so i just try which range res can work better. i try the method u provide, it s still not work.

[fanfanfan99]

hi@ jim-p,the thing u said is my
own flexible res.

[TomGeorge]

Hi, @fanfanfan99
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[jim-p]

@fanfanfan99

my
own flexible res.

If you test with an ohmmeter does it still work?

[camsysca]

@fanfanfan99 Is there a language issue here? By "own flexible res", are you really saying "my own variable res", referring to the resistance of your body?