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Sunday, January 24, 2010

Simple Breakdown Beacon Circuit

This is a simple circuit for chances of a breakdown are always greatest on a cold and windy night just when you need some sort of warning to say you are laid-up at the side of the road. This circuit is based on flip-flop concept. This is the figure of the circuit.

This type of circuit is very easy to design and is almost guaranteed to work with any type of transistor. It will also accept a wide range of values for the capacitors and resistors. It is also self-starting and uses very few components. In other words, it works superbly. A number of other flip flop circuits have been invented but they have been a flop. Some required close tolerance resistors and high gain transistors to make sure the circuit self-started and others were very complex in operation. Some of the circuits looked completely different to our “symmetrical” design and it was almost impossible to see how they worked. This is exactly what the BD 679 is. It is two transistors in one package and yet it can be treated as a single transistor as far as the circuit is concerned. This device is called a Darlington transistor, named after the inventor.

The only major difference between a single transistor and a Darlington is the turn-on voltage. For a normal transistor the turn on voltage is about .65v, while the turn on voltage for a Darlington transistor is 1.3v. In our circuit this turn-on voltage does not worry us as the circuit provides plenty of voltage for the base. The only thing we are concerned about is the turn-on CURRENT and when a Darlington transistor is used, the circuit provides sufficient base current. This is the secret behind getting this type of circuit to work and is quite often over-looked by designers.

Simple Automotive 12 V Voltage Indicator

This is a design circuit for indicating the voltage in an automotive. This circuit is a simple form of the indicator. This circuit is based on 74HCT04 as controller the circuit. This is the figure of the circuit.

When troubleshooting the 12v electrical system of an automobile, it is nice to have a simple voltage indicator tool instead of a voltmeter. This electronic circuit, hobby circuit is powered by two AA or even two N cells, which will provide enough energy for years of service. The circuit has only two leads. One lead connects to the chassis ground of the car.

The second lead can be sharp tip probe. The circuit will indicate if an automotive electrical circuit has zero volts or 12 volts present. If the voltage is near +12v, a green LED will turn on. If the voltage is near chassis ground a red LED will turn on. If the circuit is open, neither light will light. The circuit draws so little current in the open standby mode that no on/off switch is required.

Simple 1-Wire Barometer Circuit

This is a design for simple wiring barometer. This circuit has been a goal for make a simple reliable 1-Wire barometer with reasonable pressure resolution and one which could be constructed without a specialized printed circuit board by a hobbyist. This is the figure of the circuit.

This design uses a Motorola MPX4115 Silicon Pressure Sensor, a Dallas Semiconductor DS2438 Smart Battery Monitor (to perform 1-Wire analog to digital conversion), an operational amplifier, a voltage regulator, a diode, and several resistors and capacitors. The circuit requires an additional power source other than that of the 1-Wire network. The MPX4115 requires about 7 ma of current. This is more than a 1-Wire network can provide without an elaborate circuit to store parasitic power from the 1-Wire network for short burst of current for pressure measurements. For barometric pressures the MPX4115 output voltage ranges from about 4.25 to 3.79 volts at sea level, and about 2.77 to 2.45 volts at 10,000 feet. Most of this range is above the active voltage range of a 5 volt op amp circuit. In effect the sensor voltage is referenced to the power supply, not ground as desired.

To allow for this high voltage, a voltage divider is used to bring the voltage down to the active range of 5 volt op amps -- this has a gain of 0.68. This output is fed to an op amp stage, U1B, which has a gain of approximately 2.16. This stage has an adjustable voltage input which is added to the barometric sensor output within the op amp, thereby allowing the adjustment of the output voltage offset to the A/D converter. This in turn is fed to an op amp stage with a gain of U1A, capable of a gain range of 1/1 to about 8.58/1. The 10-turn potentiometers (pots) control the gain and offset. R3 controls the gain of U1A and R4 controls the offset of the output voltage.

Thursday, January 14, 2010

Simple MOSFET Tester Circuit

This is a simple design circuit for test the MOSFET condition. In this circuit included in the category astable multi vibrator. This circuit is used to test N-MOSFET (the power kind e.g irf830), whether it works or not. If it is not working, the LED will not flash. If MOSFET is working it will operate in the astable multi vibrator circuit causing the Led to flash. This is the figure of the circuit.

To make the circuit cheap, the other half of the astable utilizes an NPN transistor. This circuit can test almost any NPN transistor. As a common emitter buffer that also drives the led as it receives pulses from the MOSFET drain, this circuit uses the NPN transistor.

Diode that used in this circuit is a light emitting diode.

Simple Metal Detector Circuit

This is the design circuit for a sensing the metal. Metal detectors have two oscillators. One is tunable and the other is "Fix" with a loop. Both are "Tuned" at same frequency. Outputs from this two oscillators are then mixed in a mixer which produces only the difference. Means, if both oscillators are at the same frequency, there is nothing heard in the speaker. This is the figure of the circuit.

To start with, you need to "Zero beat" both oscillators or say "Null" them while keeping your detector in the free air, away from metal objects. Use the tuning control provided for this purpose. Once this is done, start placing detector around metal objects and you will notice that "Zero beating" is getting disturbed and an audio tone from the speaker is heard.

Simple IR Remote Control Transmitter-Receiver Circuit

This is a simple design circuit for infra red remote control transmission. This remote transmits a tone using an infra red LED. This tone is decoded by the receiver. Since the receiver only switches when it "hears" the tone, there are no accidental activations. This is the figure of the circuit.

Remote Control Setup
1. To adjust the circuit, hold down S1 while pointing LED1 at the receiver. Adjust R6 until you hear the relay click.
2. You can increase range by using a high output LED for LED1.
3. Bright light will stop the receiver from responding to the transmitter.
4. There is an error in the schematic. There should be a 1 mega ohm resistor between pin 3 of IC1 and ground. This provides a 0 volt reference to bias the IC.

Parts List
R1 - 22K 1/4W Resistor
R2 - 1 Meg 1/4W Resistor
R3 - 1K 1/4W Resistor
R4, R5 - 100K 1/4W Resistor
R6 - 50K Pot
C1, C2 - 0.01uF 16V Ceramic Disk Capacitor
C3 -1 100pF 16V Ceramic Disk Capacitor
C4 - 0.047uF 16V Ceramic Disk Capacitor
C5 - 0.1uF 16V Ceramic Disk Capacitor
C6 - 3.3uF 16V Electrolytic Capacitor
C7 - 1.5uF 16V Electrolytic Capacitor
Q1 -1 2N2222/2N3904 NPN Silicon Transistor
Q2 -1 2N2907 PNP Silicon Transistor
Q3 - NPN Phototransistor
D1 - 1N914 Silicon Diode
IC1 - LM308 Op Amp IC
IC2 - LM567 Tone Decoder
LED - 1 Infa-Red LED
RELAY - 6 Volt Relay
S1 - SPST Push Button Switch
B1 - 3 Volt Battery Two 1.5V batteries in series
MISC - Board, Sockets For ICs, Knob For R6, Battery Holder
RELAY - 6 Volt Relay

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