# Not enough current for voltage divider?

I'm trying to use a HIH4030 humidity sensor, where the output value is provided to a XBee.

Considering that output sensor max output voltage is around 4V and the XBee ADC only supports 1,2V, I took some time to choose the correct resistors for a voltage divider to get a decent ratio. I end up choosing a 120 ohm and a 270 ohm resistors to get a ratio of 4V to 1V.

And in this case I wasn't getting any values on my XBee. When I measured the signal, I had about 31mV going out the voltage devider when I should have around 800mV.

Now, correct me if I'm wrong (and there's a good chance that's the case), but the reason for these low values are due to the low total resistance value (R1+R2 = 390ohm) and the low current value going out the sensor. The HIH4030 specs say that the current supply varies from 200uA to 500uA, so I'm assuming that from this sensor I won't get higher currents than 500uA. Is this a correct assumption?

Anyway, taking this assumption as the correct one, through ohms law,

V=RI. V=390*0.0005, thus V=195mV which is hardly enought.

I was considering getting higher resistance values, at least to a total of R=1,2/0.0005.

Am I proceeding correctly?

• It's the parallel combination of the two divider resistors: $$\frac{1}{1/12k + 1/27k} = 8.3k$$ Commented May 1, 2014 at 1:05