I m a newbie in these things so please excuse my knowledge.
I ve a K8055 card. I bought a pressure sensor (FSR-174N).
It is changing it s resistance from 3kOhm to 2MOhm depending on how hard you press. I attached one strip to the analog input 1 and the other to the gnd. The internal voltage between the analog input 1 and gnd is 5V. If I press to the sensor the voltage decrease to e.g. 3.5v but at the demo software (coming with the k8055) is nothing changeing :?
In the software I just can change the scrollbar if i turning at the resistance on the card.
What i ve to do to get the value from my pressure sensor?
Look the circuit diagram on page 21 of the manual.
There you can see that the input A1 is not effective if jumper SK2 is mounted.
To get the A1 input working you have to remove the jumper SK2 and turn the RV1 to its maximum position clockwise.
Furthermore, you need to add a pull-up resistor (about 10k) between A1 input and +5V.
You get the +5V from connector A2. Keep the jumper SK3 mounted and only SK2 removed.
Simply connect your sensor between A1 and A2 connectors. The potentiometer RV1 acts as a pull-down resistor in this case.
If you like to measure more accurately high pressures add a 10k resistor between A1 and GND.
yeah man, it works!
now there is sth weird, I have diffrent wieghts, 15g, 25g, 35g and 45g if I put e.g. the 35g on the sensor i get diffrent result in every messure, sometimes i get 115 then 130, 140 when i read the analog input in. Why is this changeing every time?
It is possible that you get hum pickup somewhere due to connection leads. As this is a rather high-impedance circuit, it is very likely. It might need additional filtering. Furthermore, I’ve checked the datasheet of the pressure sensor. It features a large amount of applications info, but it is clear that it is not for novices. You will have to experiment a lot in order to obtain reliable and repeatable results.
As VEL417 says you may need additional filtering.
If you can accept some delay to the measurement result, you can try to reduce the result fluctuation by adding an electrolytic capacitor of 10uF…100uF between the A1 input and GND.