Converting resistance to voltage in electronics sometimes are so important. This happens because many electronics device such as microcontroller only can read voltage as analog input signal. Analog signal then will be converted to digital using ADC. But before we talk about ADC or microcontoller, how if our sensor has resistance output instead of voltage?
Voltage Divider as resistance to voltage converter
The only thing we can do to make our sensor readable by microcontroller is convert resistance to voltage. Converting a resistance to voltage is far more easier than converting to other quantity. So, how we do that?
The answer is very simple. Use voltage divider !
Voltage divider has capability to divide the voltage by comparison of two resistance. You can read more details about voltage divider here.
I use an LDR for a light sensor. LDR has linear resistance to the light that exposed to it surface. When light getting brighter, the resistance will decreased. Otherwise when light brightness dercreases the resistance will increases. Here’s my schematic example:
The output voltage will be :
In this example, when light density is changed, the LDR resistance will changed too and of course Voltage output will changed accordingly.
Since the voltage will change in every change of light density, then you can connect this voltage output to an microcontroller ADC.
Pick the right R2 has a little trick. You have to choose the closest one to LDR reistance range to make the voltage output difference better. For example, if your LDR resistance will vary between 800 ohm to 1k ohm then used 1k ohm resistor as R2 will be ok. But if you has LDR with resistance output vary from 8k-10k don’t use 1k as R2, using 10k as R2 will better.