Showing posts with label explained. Show all posts
Showing posts with label explained. Show all posts
Sunday, April 7, 2013
Simple Delay Timer Circuits Explained
In many electronic circuit applications a delay of a few seconds or minutes becomes a crucial requirement for ensuring correct operation of the circuit. Without the specified delay the circuit could malfunction or even get damaged.
Here we discuss how we can make simple delay timers using very ordinary components like transistors, capacitors and diodes.
Lets analyze the various configurations in details.
The first circuit diagram shows how a transistors and a few other passive components may be connected for acquiring the intended delay timing outputs.
The transistor has been provided with the usual base resistor for the current limiting functions.
A LED which is used here just indication purposes behaves like the collector load of the circuit.
A capacitor, which is the crucial part of the circuit gets the specific position in the circuit, we can see that its been placed at the other end of the base resistor and not directly to the base of the transistor.
A push button is used to initiate the circuit.
On depressing the button momentarily, a positive voltage from the supply line enters the base resistor and switches ON the transistor and subsequently the LED.
However in the course of the above action, the capacitor also gets charged fully.
On releasing the push button, though the power to the base gets disconnected, the transistor continues to conduct with the aid of the stored energy in the capacitor which now starts discharging its stored charge via the transistor.
The LED also stays switched ON until the capacitor gets fully discharged.
Te value of the capacitor determines the time delay or for how long the transistor stays in the conducting mode.
Along with the capacitor, the value of the base resistor also plays an important role in determining the timing for which the transistor remains switched ON after the push button is released.
However the circuit using just one transistor will be able to produce time delays which may range only for a few seconds.
By adding one more transistor stage (next figure) the above time delay range can be increased significantly.
The addition of another transistor stage increases the sensitivity of the circuit, which enables the use of larger values of the timing resistor thereby enhancing the time delay range of the circuit.
Two Step Sequential Timer
The above circuit can be modified to produce a two step sequential delay generator. This circuit was requested by one of the avid readers of this blog, Mr.Marco.
Here we discuss how we can make simple delay timers using very ordinary components like transistors, capacitors and diodes.
Lets analyze the various configurations in details.
The first circuit diagram shows how a transistors and a few other passive components may be connected for acquiring the intended delay timing outputs.
The transistor has been provided with the usual base resistor for the current limiting functions.
A LED which is used here just indication purposes behaves like the collector load of the circuit.
A capacitor, which is the crucial part of the circuit gets the specific position in the circuit, we can see that its been placed at the other end of the base resistor and not directly to the base of the transistor.
A push button is used to initiate the circuit.
On depressing the button momentarily, a positive voltage from the supply line enters the base resistor and switches ON the transistor and subsequently the LED.
However in the course of the above action, the capacitor also gets charged fully.
On releasing the push button, though the power to the base gets disconnected, the transistor continues to conduct with the aid of the stored energy in the capacitor which now starts discharging its stored charge via the transistor.
The LED also stays switched ON until the capacitor gets fully discharged.
Te value of the capacitor determines the time delay or for how long the transistor stays in the conducting mode.
Along with the capacitor, the value of the base resistor also plays an important role in determining the timing for which the transistor remains switched ON after the push button is released.
However the circuit using just one transistor will be able to produce time delays which may range only for a few seconds.
By adding one more transistor stage (next figure) the above time delay range can be increased significantly.
The addition of another transistor stage increases the sensitivity of the circuit, which enables the use of larger values of the timing resistor thereby enhancing the time delay range of the circuit.
Two Step Sequential Timer
The above circuit can be modified to produce a two step sequential delay generator. This circuit was requested by one of the avid readers of this blog, Mr.Marco.
A simple delay OFF alarm circuit is shown in the following diagram.
The circuit was requested by Dmats.
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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