Voltage Error on OUT1000

[phischmi]

Hi all,
i've made a simple circuit to control a pc fan.
The circuit is based on an ATtiny85, which measures the voltage on its Pin3 and then sends a corresponding pwm signal to the fan.



I control the voltage on Pin3 via an OUT1000, where 0V is OFF and 4.2V equals 100% power. This works great so far

There is just one thing i can't explain to myself:
When trying different voltages via the Phidget-Tool i get several "Voltage Errors" at around ~3.0V. This error occurs when there is a voltage drop because of a higher current draw. But since i'm just measuring the voltage, there should be no higher current draw
To be clear, the ATtiny only measures the adjacent voltage on its Pin3. The fans power comes from one separate 12V source, which also powers the ATtiny itself.

Do you guys have any ideas, why this error occurs?


Thanks in advance.

Philipp

[Patrick]

Hi,

See here: https://www.phidgets.com/?tier=3&catid= ... nd_Sinking

Your ATtiny85 should not be drawing anywhere near enough current to cause a voltage error.

Have you also connected the ground between the OUT1000 and your circuit?

-Patrick

[phischmi]

Hi Patrick,
yes, grounds are connected.

[phischmi]

Hi,
the errors only occur between 3.07V nd 4.1V, by the way.

This is the circuit i built:


And everything soldered together:


The one 10kOhm resistor at the bottom was added afterwards, because of the 100nF capacitor before the ATtinys analog in...
Removing this resistor makes no difference to the described errors.

Maybe this info helps.


Regards

Philipp