I'm a beginner at this.  If my hand adds capacitance and I charge up to=20
the same voltage then I would have more charge.  The rate of the charge=20
bleed of is dependant on the light shining on the LED and a bit on the=20
high impedance of the input pin.  My thought was if it was a capacitance=20
effect then the count should increase with my hand on the wires, which=20
is opposite of what I am seeing.

Gordon


On 16-09-18 06:22 AM, Isaac M. Bavaresco wrote:
> Gordon,
>
> Q =3D C * V    <=3D>    V =3D Q  / C
>
> You have a fixed amount of charge (that is bleeding off quickly), so if
> you increase the capacitance then the voltage will drop.
>
> Isaac
>
>
>
> Em 17/09/2016 23:35, Gordon Williams escreveu:
>> Hi,
>>
>> I have an arduino nano where I am using a red LED for a light sensor.
>> It seems to be working well and has good sensitivity, but there is some
>> effect that I don't understand.  I hope someone can provide an explanati=
on.
>>
>> The setup consists of an LED with a 220 Ohm resistor soldered to one of
>> the legs.  The light/resistor than gets connected to pins 7 and 8 on the
>> board through a pair of twisted wires.  I reverse bias the LED to charge
>> it up then change the positive pin to an input and read it in a loop
>> while counting how long it takes to go from high to low as the charge
>> bleeds off the LED.  The more light shining on the LED the faster the
>> pin goes from high to low and the lower the resulting count.  All this
>> works as expected.
>>
>> The thing that I don't understand is when I touch the twisted wires the
>> count decreases indicating that the charge is bleeding off faster.  I
>> understand that there is likely a capacitance effect from having my hand
>> close to the wires, but I would have though that this would have
>> increased the capacitance and therefore this should have taken longer
>> for charge to bleed off and not shorter.  Does the fact that they are
>> twisted have anything to do with it?  If I wet my fingers before I touch
>> the wires it seems to become a lot more sensitive to touch as you almost
>> don't have to touch the wires before you see the effect.
>>
>> Thanks,
>>
>> Gordon Williams
>>
>>
>>
>>

--=20
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