Steam sensor

Here is the circuit diagram of a simple steam sensor, wired around a handful of inexpensive components. This steam sensor can be connected to a microcontroller’s I/O port directly. The steam sensor works by having a sensor pad with series of exposed traces connected to ground rail, and interlaced traces between the grounded traces connected to the input of a comparator. The output voltage will change when the humidness of the sensor pad surface goes up. There is also an onboard potentiometer to adjust the system sensitivity. You even could use it as a rain/moisture sensor.

Features

• Low power consumption
• Adjustable sensitivity
• Onboard status indicators
• Digital and Analog output
• uC-compatible operating voltage: VCC = 5V

In the prototype, the home-made sensor pad – built from a rectangular copper clad board with the pattern etched as shown below – has a dimension of 4×3 cm. However, you are free to build your own sensor pad as per your requirement and taste.

steam sensor pad

Here, one-part of the LM393 (IC1) works as the voltage comparator, a reference voltage at the inverting input (pin 2 of IC1) is set by the multi-turn potentiometer (P1). When the analog value, inputted to the non-inverting input (pin 3 of IC1) from the sensor pad goes beyond this pre-setted value, IC1 will output a digital value to indicate that the setup threshold value is reached, and the sensor is activated.

Note that, this steam sensor circuit offers two outputs; Digital (DO) and Analog (AO). If you only want a logic-low (L) level output when a threshold is reached, just use the Digital (DO) output. But if you are looking for a varying voltage value as the output to indicate the sensing parameters, the Analog (AO) output is your best option. The green-LED (LED1) works as the power-on indicator, and the red-LED (LED2) indicates active-state of the sensor circuit.

LM393 datasheet

As stated, the steam sensor circuit is based on a single comparator in the LM393 (IC1). Similar to an operational amplifier (op-amp), the comparator has inverting (–) and non-inverting (+) inputs. If the noninverting input is at a higher voltage than the inverting input the output goes high, and if the inverting input is at the greater voltage the output goes low. This is again the same as for an opamp, but there is a subtle difference in that the output stage of a comparator is usually an open collector type, that is to say, there is a switching transistor at the output that can used to control an external load of some kind.

The inverting input (–) of the comparator is fed with a pre-setted fixed voltage, and the non-inverting input (+) is fed from the sensor pad. In case of a steam detection, a certain fraction of the supply voltage is therefore fed to the non-inverting input, and this fraction is controlled by the humidity level on the sensor pad surface. If the potential fed to the non-inverting input falls, and the inverting input is at a higher voltage, the output transistor of the comparator switches on and a logic-low level is outputted through the comparator’s output terminal.

Construction of the circuit is extremely simple indeed, and it should be within the capabilities of complete beginners. To some extent the way in which the unit is constructed and used will depend on the precise application. It can be built into a small plastic or metal box and connected to the sensor pad via a twin lead. In most cases, however, it is more likely to be incorporated into another project. For highly critical applications the threshold levels can be “fine tuned” by tweaking the values of resistors R1, P1 and ofcourse by changing the dimension/track layout of the sensor pad.

HELP TAKEN:-

http://www.electroschematics.com/