I am using LM3914 for testing soil moisture content. Based on the water content, the output of the IC needs to reflect.I am using the IC in the bar mode.
Now, the issue that i am facing is that, when the LED is OFF(i.e.OUTPUT IS OFF) and when the LED is ON (i.e. OUTPUT PIN IS ON), there is a very small difference in the voltage on the PIN.
I need 2 distinct voltages- 1)Greater than 3.1 V 2) GND(<0.8V) since i need to connect the output pins of the IC to a communication circuit.
Could anyone please help me?
Best Answer
Replace the LED you want to monitor with an opto-isolator. The photo-transistor will give you the logic levels you require - although they may be inverted from the way you would like.
simulate this circuit – Schematic created using CircuitLab
This also has the benefit that you can isolate the two circuits. The soil probe negative rail can not be grounded without interfering with the circuit operation.