Showing posts with label sensor. Show all posts
Showing posts with label sensor. Show all posts
Thursday, April 11, 2013
Infrared IR Proximity Distance Sensor Circuit
The photodiode can be used to detect IR reflected from the object. However, IR produced by the ambient conditions also detected by the photodiode. This IR noise must be filtered to prevent false detections. Usually, the LED’s IR signal is modulated with a convenient frequency and then using that modulation to detect only IR to filter the IR noise. So, the photodiode will detect only IR reflected from the object. This method can be simplified by using the IR proximity sensor that has simple receiver and transmitter sections. This is the figure of the circuit;
The transmitter of this circuit consists of a 940nm IR LED (IR11-21C). To turn ON and OFF the IR LED, the a 10kHz oscillator frequency is used. we can control the detection and the level of transmitted power by varying the LED current. The transmit pulses of this transmitter have a small duty cycle (typically 10%), to save power.
The Op amp is biased at 2.5V because there no input IR signal present. The op amp output varies around 2.5V with a dynamic range of 5V because of a 10kHz IR signal incident. The output drives a simple diode detector. A DC signal proportional to its amplitude can be provided by a simple diode detector. Simple diode detector also rectifies the 10kHz signal. The output signal is an analog signal that is proportional to the distance of the object from the IR transmitter. We can fed the output signal to an ADC for further processing or use it directly.
[Circuit source: MAXIM Application Note]
Wednesday, April 10, 2013
Simple Heat Sensor Circuit Diagram
This simple heat sensor circuit could senses heat from various electronics device like computer, amplifier etc. and generate warning alarm. It could senses heat from environment also, but here I mention “electronics device” because it is being using mostly in electronic device to protect them from overheat.
Thermistor, 110 Ohms:
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| Fig-2: 110 Ohms Thermistor |
As it is a heat sensor circuit, here a thermistor is used as a heat sensor. It is a thermal measurement device and has a variety of usages including temperature sensor/ heat sensor. The thermistor used in this circuit is a NTC (Negative Temperature Coefficient) type thermistor. When temperature increases, its resistance goes decrease. Therefore, NTC thermistor’s resistances are inverse of temperature.
Circuit Description:
You have seen, in this simple circuit diagram of heat sensor, a few number of components is used including a BC548 transistor, a 110 ohms thermistor etc.- BC548: BC548 is a TO-92 type NPN transistor, as its alternative you can use 2N2222, BC238, BC548, BC168, BC183 etc. they all have almost same characteristic.
- 110 Ohms Thermistor: A 110 Ohms thermistor is used to detecting heat. I have told already about it.
- Buzzer: A buzzer is used with +9V and collector of transistor. When the temperature/ heat exceeds a certain level then it make an alarm.
- 4.7V Zener diode: It is used to limit the emitter current of BC548.
- 9V Battery: A 9V battery is used as a single power source.
- R1, R2: A 3.3K 1/4w resistor is used as R1 and 100 ohms 1/4w as R2.
- Switch: Here in this circuit the switch used is a simple SPST switch. You can either use the switch or not, choice is yours. It is not mandatory.
Friday, April 5, 2013
Fire alarm with light sensor
Fire alarm can be made with a light sensor (LDR) as in the article with the title of Fire Alarm with this LDR sensor. Principles of fire detection Fire Alarm with LDR sensor is to detect the presence of smoke through the LDR. LDR in the series Fire Alarm does not stand alone in detecting a fire, but the LDR in the pair with the light shining on the LDR.
Hence, in the detected smoke from the fire then the intensity of light received by the LDR LDR decreases and eventually trigger an alarm system on a series of Fire Alarm with this LDR sensor. Part 2 that in the series of Fire Alarm with Sensor LDR are some of the sensors, tone generator, audio power.
Image Series Fire Alarm with Sensor LDR
Function Section of the Fire Alarm with Sensor LDR
Part of LDR and light sensor facing to fire smoke detection
Part trigger using transistors and regulators as a trigger tone generator 7805
Tone generator section with IC UM66
Power audio section uses an audio power IC TDA 2002 which is equipped with voleme control (R3)
Thursday, April 4, 2013
Precision Temperature Sensor IC LM35 Explained Celsius Sensor
The IC LM35 is a precision temperature sensor device, which generates linearly proportional output in response to the rising or falling ambient temperature, directly in Celsius.
Understanding the Specs of Temperature Sensor IC LM35
This feature of producing outputs directly in Celsius gives this device an significant edge over the other types of sensors which are based on degree Kelvin, where a conversion to Celsius becomes a relatively complex issue.
The IC LM35 does not need any external setting or adjustments for obtaining accurate results within +/-1/4 degree Celsius at temperatures of room level and at +/-3/4 degree Celsius between a complete -55 to +150 degree Celsius range of temperature.
The IC LM35 has features like linearly varying output, low output impedance and precise built-in calibration arrangement which makes the device very easy and ideally suitable for interfacing with all types of control circuits.
The IC is able to function with dual supplies or even with single polarity power supplies.
A low 60 uA consumption by this IC inhibits the IC from self heating, which amounts to 0.1 degree Celsius in constant air.
The IC LM35 has a good -55 degrees to +150 degrees Celsius sensing range.
The IC comes in a hermetically sealed TO-46 package, other ICs in the series like the LM35C, LM35CA, and LM35D come in the transistor type package of TO-92.
The LM35D comes also in the 8-pin surface laid small outline package and in TO-220 enclosure.
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