K8055 and humidity sensor

Kits PC Related Projects
#1

hi has anyone managed to measure humidity with the analog inputs of the k8055, i have tried several different sensors without a lot of luck, i bought a honeywell hih 4000 series which jumps 10 or 20 percent every half minute or so, i also noticed on the data sheet that the max output of the hih 4000 was 4v, i thought it was 5v so without a lot of grief it won’t work

can anyone recommend a humidity sensor/ module that will work with my k8055 ???

thanks for any help

dave

#2

The output of the HIH-4000 may be too “weak” to drive the input of the K8055. There is 100k ohm resistance (RV1, RV2) between the inputs and the GND of the K8055.
You can check whether this is the case:

  1. Disconnect the sensor output from the K8055 analog input and use a DVM to measure the output voltage of the sensor.
  2. Connect the output of the sensor to the K8055 input and measure again the output voltage of the sensor.

If the voltage in the second case is lower than the voltage in the first case, then the 100k load is too heavy for this humidity sensor.

[quote]i also noticed on the data sheet that the max output of the hih 4000 was 4v, i thought it was 5v so without a lot of grief it won’t work[/quote]This is no problem - you can easily increase the gain of the K8055.

#3

thanks vel 255,
i have measured the hih 4000 voltage disconnected from k8055 3.12v and again when connected 2.60v and there is a voltage drop so the resistive load on the input is too high…

is there a way of making the analog input number 2 have no resistive load ?? or a lower one ( if that even works )
maybe a link wire across vr2 or ATT2 as printed on pcb…

thanks for your help
dave

#4

Indeed, it seems that the 100k input resistance of the K8055 is too low for the HIH-4000.

[quote]is there a way of making the analog input number 2 have no resistive load[/quote]Yes, it is.
You can do it by removing RV2.
Place a jumper wire according to this drawing:

799×488

#5

thanks vel 255

i have linked across rv2 but still have a 0.5v drop when attaching the hih400 to k8055

another question if i may ,

why does the humidistat’s voltage drop when i raise the humidity ??? i have wired the hih4000 +5v to the top pin of Sk3 on k8055 gnd to gnd and the output of hih4000 (via a breadboard so i can measure voltage ) to analog input 2 of k8055.

cheers for your rapid response

#6

You have to remove the trimpot RV2 to avoid the 100k load.
Then add the jumper wire between the two soldering points of removed RV2.

#7

thanks vel 255

didn’t realise i had to remove the pot

thanks

#8

that worked, there is no voltage drop when i attach or remove the connection from the k8055

thanks a lot vel 255

#9

i am getting a extended usb interface board K8061 soon, will i have the same problem with voltage drop like i did with the k8055.

#10

You can avoid the problem by not installing the resistor array RA4.
Here is the link to download the circuit diagram: box.net/shared/2o4jxf9yuu