Konstanta gas

Konstanta gas

Konstanta gas (disebut juga konstanta gas ideal, molar, semesta, atau universal, biasanya dilambangkan dengan huruf R) adalah sebuah konstanta fisika yang sering muncul dalam banyak persamaan fundamental fisika, seperti hukum gas ideal dan persamaan Nernst. Konstanta ini ekuivalen dengan konstanta Boltzmann, tetapi dinyatakan dalam satuan energi per kelvin per mol (daripada energi per kelvin per partikel).

Harganya adalah:

R = 8.314472(15) J · K^-1 · mol^-1

Dua digit di dalam kurung adalah ketidakpastian (deviasi standar) pada harga dua digit terakhir.

Konstanta gas didapatkan dari persamaan keadaan paling sederhana, hukum gas ideal, sebagai berikut:

dengan:

adalah tekanan absolut

adalah temperatur absolut

adalah volume "ruang" yang ditempati

adalah jumlah gas (jumlah molekul gas, biasanya dalam mol)

adalah volume molar

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Simple switch-Off Time Delay Circuit

Designing a switch off delay circuit is quite simple and will cost you no more than $5 to make. All parts can be picked up from Radio Shack or Fry's if you have them as well as Parts Express. This will cover the mechanical aspects of it - theoretical topics can come later. If you suffer from pops on your amps or any other components, this will help you eliminate it, but it does not work in all cases.

Simple switch-Off Time Delay Circuit

Designing a swictch off delay circuit is quite simple and will cost you no more than $5 to make. All parts can be picked up from Radio Shack or Fry's if you have them as well as Parts Express. This will cover the mechanical aspects of it - theoretical topics can come later. If you suffer from pops on your amps or any other components, this will help you eliminate it, but it does not work in all cases.

The two circuits di atas illustrate opening a relay contact a short time after the ignition or ligh switch is turned off. The capacitor is charged and the relay is closed when the voltage at the diode anode rises to 12 volts. The circuit on the left is a common collector or emitter follower and has the advantage of one less part since a resistor is not needed in series with the transistor base. However the voltage across the relay coil will be two diode drops less than the supply voltage, or about 11 volts for a 12.5 volt input. The common emitter configuration on the right offers the advantage of the full supply voltage across the load for most of the delay time, which makes the relay pull-in and drop-out voltages less of a concern but requires an extra resistor in series with transistor base. The common emitter (circuit on the right) is the better circuit since the series base resistor can be selected to obtain the desired delay time whereas the capacitor must be selected for the common collector (or an additional resistor used in parallel with the capacitor).

The time delay for the common emitter will be approximately 3 time constants or 3*R*C. The capacitor/resistor values can be worked out from the relay coil current and transistor gain. For example a 120 ohm relay coil will draw 100 mA at 12 volts and assumming a transistor gain of 30, the base current will be 100/30 = 3 mA. The voltage across the resistor will be the supply voltage minus two diode drops or 12-1.4 = 10.6. The resistor value will be the voltage/current = 10.6/0.003 = 3533 or about 3.6K. The capacitor value for a 15 second delay will be 15/3R = 1327 uF. We can use a standard 1000 uF capacitor and increase the resistor proportionally to get 15 seconds.

Source: bowdenshobbycircuits.info

Regulator Variable Sederhana

A simple but less efficient method of controlling a DC voltage is to use a voltage divider and transistor emitter follower configuration. The figure below illustrates using a 1K pot to set the base voltage of a medium power NPN transistor.

Skema Rangkaian Regulator Variable Sederhana

The collector of the NPN feeds the base of a larger PNP power transistor which supplies most of the current to the load. The output voltage will be about 0.7 volts below the voltage of the wiper of the 1K pot so the output can be adjusted from 0 to the full supply voltage minus 0.7 volts. Using two transistors provides a current gain of around 1000 or more so that only a couple milliamps of current is drawn from the voltage divider to supply a couple amps of current at the output.

Note that this circuit is much less efficient than the 555 timer dimmer circuit using a variabe duty cycle switching approach. A fairly large heat sink is required to prevent the PNP power transistor from overheating. The advantage of the circuit is simplicity, and also that it doesn't generate any RF interference as a switching regulator does. The circuit can be used as a voltage regulator if the input voltage remains constant.

220V AC Ultra Bright LEDs lamp Circuit

This ultra-bright white LED lamp works on 230V AC circuit with minimal power consumption. Ultra-bright LEDs available in the market cost Rs 8 to 15. These LEDs emit a 1000-6000mCd bright white light, like the welding arc and work on 3 volts, 10 mA. Their maximum voltage is 3.6 volts and the current is 25 mA. Anti-static precautions taken Pls Should Be handling the LEDs. The LEDs in a water-clear plastic package emit spotlight, while diffused type LEDs have a wide-angle radiation pattern.

220V AC Ultra Bright LEDs lamp Circuit

The schematics circuit of above employs capacitive reactance for limiting the current flow through the LEDs on the application of mains voltage to the circuit. We use only if a series resistor for limiting the current with mains operation. The 100-ohm, 2W resistor series avoids heavy 'inrush' During current transients. MOV at the input prevents surges or spikes, protecting the circuit. The 390-kilo-ohm, ½-watt resistor acts as a bleeder to Provide discharge path for capacitor Cx Pls mains supply is disconnected. The zener diode at the output section prevents excess levels of reverse voltage appearing across the LEDs During the negative half-cycles. During the positive half cycle, the voltage across the LEDs is limited to the zener voltage.

16-LED/46-LED combination

Aseries combination of 16 LEDs Gives a luminance (lux) equivalent of a 12W bulb. But if you have two series combinations of 23 LEDs in parallel (Total 46 LEDs), it Gives equal to a 35W light bulb.

Diode D1 (1N4007) and capacitor C1 act as rectifying and smoothing elements to Provide DC voltages to the row of LEDs. For a 16-LED row, use Cx of 12:22 μF, 630V; C1 of 22 μF, 100V; and zener of 48V, 1W. Similarly, for 46 LEDs combination use Cx of 0:47 mF, 630V; C1 of 33 μF, 150V; and zener of 69V, 1W. This circuit (inclusive of LEDs) costs Rs 200 to Rs 400.

10 LED VU Meter Using IC LM3914

This 10 LED VU meter circuit has only a few parts but is useful as an indicator for the measurement of entering acoustic signals. The circuit is a perfect one chip replacement for the standard analog meters. It is completely solid state and will never wear out

LM3914 VU Meter Circuit

The circuit is built around an LM3914 IC. The input signal from the VU meter is put on pin 5 of IC1. Through pin 9 of IC1 is the display mode sets (bar or dot instructions). In the drawn state IC1 works in the dot mode. When pin 9 is coupled to pin 3, the IC works in bar mode. Obviously the whole circuit consumes less power in dot mode.

List Component

C1        : 2.2uF/ 25V Electrolytic Capacitor
R1        : 1K  Resistor
D1        : 1N4002 Diode
LED1-LED  : 10 x  LED or LED Array
U1        : LM3915 

Notes

• V+ can be anywhere from 3V to 20V. 
• The input is designed for standard audio line voltage with has a maximum input voltage of 1.3V.
• Pin 9 can be disconnected from ground to make the circuit use a moving dot display instead of a bar graph display.

Light/Dark Switch With Relay

Thursday, May 19, 2011

Light/Dark Switch With Relay

The circuit as shown act as a light detector. Under normal conditions the resistance of the LDR is high, keeping pin 2 low. When light falls onto the LDR the resistance drops to a couple hundred ohms and triggers pin 2 high which biases the base of Q1 via pin 6 and R4 and in turn activates the relay.

Light/Dark switch Circuit with relay

As you may have notice, the 741 is connected as a voltage comparator. Two voltage dividers are easy to be found: The first one is the10K resistor and the LDR . The second one is composed by the two 470 Ohms resistors and the potentiometer. Both the outputs of the dividers are connected as inputs to the voltage comparator.

The second voltage divider will settle the reference voltage. The first voltage comparator that contains the LDR, will change it's voltage according to the light level. When the voltage across the negative input of the comparator is less than the voltage to the positive input of the comparator, the output is held low. When the voltage on the negative input rises, there will be a time that it becomes greater than or equal to the positive (pre-selected) voltage, and then the output becomes high and the relay through the 2N2222 is actuated.