K8055 Analog input question


#1

Using the demo software that comes with this project:

Leaving the jumpers for the analog inputs connected and adjusting the potentiometers, I can move the scroll bar all the way from 0 - 255. However, when I remove the jumpers and connect an external voltage (measured with an accurate multimeter). The voltage has to be set at +10V in order to reach the maximum value (255) on the scroll bar. The manual clearly states that +5V DC is the maximum that should be applied to the inputs.

What is going on here? I have not used either of the ‘gain’ resistors as 0-5V input is fine for what I need.

Im sure I must be doing somthing stupid…

Cheers, Scott.


#2

i think you can use the pot meters to control the min/max. This impacts the scroll bar when getting an ‘steady’ input voltage.

At least for me that works; i had the same “problem”

Regards,
Bert


#3

Make sure the potmeters are set fully clockwise (255 with jumper in place).
Check your gain resistors, maybe they are the wrong value.

If all the above is OK, check your voltage source. If it’s output impedance is too high (e.g. due to a series resistor or high impedance potmeter), R3 and RV1 will act as a voltage divider and lower the voltage.


#4

Thanks guys, you where correct - I hadn’t turned the pots fully clockwise. Strange it doesn’t mention that in the instructions. Problem solved!