circuit wiring: sensor

Showing posts with label sensor. Show all posts

Wednesday, September 25, 2013

Tiny Dew Sensor

Dew (condensed moisture) adversely affects the normal performance of sensitive electronic devices. A low-cost circuit described here can be used to switch off any gadget automatically in case of excessive humidity. At the heart of the circuit is an inexpensive (resistor type) dew sensor element. Although dew sensor elements are widely used in video cassette players and recorders, these may not be easily available in local market. However, the same can be procured from authorized service cent res of reputed companies. The author used the dew sensor for FUNAI VCP model No. V.I.P. 3000A (Part No: 6808-08-04, reference no. 336) in his prototype.

In practice, it is observed that all dew sensors available for video application possess the same electrical characteristics irrespective of their physical shape/size, and hence are interchangeable and can be used in this project. The circuit is basically a switching type circuit made with the help of a popular dual op-amp IC LM358N which is configured here as a comparator. (Note that only one half of the IC is used here.) Under normal conditions, resistance of the dew sensor is low (1 kilo-ohm or so) and thus the voltage at its non-inverting terminal (pin 3) is low compared to that at its inverting input (pin 2) terminal.

The corresponding output of the comparator (at pin 1) is accordingly low and thus nothing happens in the circuit. When humidity exceeds 80 per cent, the sensor resistance increases rapidly. As a result, the non-inverting pin becomes more positive than the inverting pin. This pushes up the output of IC1 to a high level. As a consequence, the LED inside the opto-coupler is energized. At the same time LED1 provides a visual indication. The opto-coupler can be suitably interfaced to any electronic device for switching purpose. Circuit comprising diode D1, resistors R8 and R6 and capacitor C1 forms a low-voltage, low-current power supply unit. This simple arrangement obviates the requirement for a bulky and expensive step-down transformer.

Friday, April 5, 2013

Water Level Sensor Circuit Using LM1830 Single Chip

This is a water sensor circuit design using based on a Conductive Liquid Level Sensor, this single chip circuit is very compact and simple. This circuit is an ac excited fluid level sensor, which uses alternating current to provide biasing for the sensor probe to avoid electrolysis of the probes. This ac excitation makes the sensing probe has longer lifetime. This circuit can be useful for wide range of water or liquid level sensing and control such as radiators, beverage dispensers, washing machines, water softeners, irrigation, reservoirs, boilers, aquarium, or sump pumps

Many type of fluids are electrically conductive and can be detected using this liquid level sensor circuit: city water/ground water, sea water, chopper sulfate solution, weak acid, weak base, household ammonia, water and glycol mixture, wet soil, coffee, or fruit juices. Remember that most of fuel doesn’t conduct electricity, so this circuit can be employed as fuel level sensor/detector. This is the figure of the circuit.

If we look at its data sheet, this water level sensor circuit chip is best at 10-24 volt supply voltage. The absolute maximum voltage supply for this liquid level sensor chip is 28V, but remembers to always try to avoid this extreme condition to prevent damaging the chip.

In the first circuit, a basic low level warning application uses a LED to indicate the water level falls below the sensor. You can see the filter pin (9) is not connected, this means that the LED is actually blinking at sound frequency, but it’s fine since our eye response is slow enough to notice such high speed blinking. Since without filter capacitor at pin 9 the output give a square wave signal, you can easily replace the led with loud speaker as shown in the second circuit to give audio indication. If you need a TTL or CMOS level then you should use a filtering capacitor connected to pin 9 and use the open collector output to drive a pull up resistor connected to a voltage supply at desired voltage level. For water level control, or any conductive liquid level control, you can use a relay to activate a motor or valve to control the level. The third circuit show this kind of application, and the relay can be seen as liquid/water level switch. The optional resistor seen in the third circuit is an option for high voltage transient that often occurs in automotive environment, and you can omit it if there is no such possibility. [Circuits schematic diagram source: National Semiconductor Application Notes]

Wednesday, April 3, 2013

Fire Sensor Hamamatsu UVTRON

Fire Sensor (Hamamatsu UVTRON)

UVTRON Hamamatsu R2868 is a sensor that detects a flame fire that emit ultraviolet light. Ultraviolet light emitted from a candle flame is a 5 meter can be detected by this sensor. This sensor can also detect some unseen phenomena such as high voltage transmission.

In order for this UVTRON sensors to connect to the system microcontroller then required a series of lawyer-signal condition that serves to change the response of UVTRON into pulses that can be recognized by the system microcontroller. With Module C3704 UVTRON response will then be processed into about 10 pulses mS and the maximum current 100mA. The output module uses the open configuration collector.