Signals when an on-circuit battery is exhausted 5V to 12V operating voltage

A Battery-status Indicator circuit can be useful, mainly to monitor portable Test-gear instruments and similar devices. LED D1 flashes to attire the users attention, signaling that the circuit is running, so it will not be left on by mistake. The circuit generates about two LED flashes per second, but the mean current drawing will be about 200µA. Transistors Q1 and Q2 are wired as an uncommon complementary astable multivibrator: both are off 99% of the time, saturating only when the LED illuminates, thus contributing to keep very low current consumption. 

Circuit diagram :

Flashing-LED Battery-status Indicator Circuit Diagram

The circuit will work with battery supply voltages in the 5 - 12V range and the LED flashing can be stopped at the desired battery voltage (comprised in the 4.8 - 9V value) by adjusting Trimmer R4. This range can be modified by changing R3 and/or R4 value slightly.

When the battery voltage approaches the exhausting value, the LED flashing frequency will fall suddenly to alert the user. Obviously, when the battery voltage has fallen below this value, the LED will remain permanently off. To keep stable the exhausting voltage value, diode D1 was added to compensate Q1 Base-Emitter junction changes in temperature. The use of a Schottky-barrier device (e.g. BAT46, 1N5819 and the like) for D1 is mandatory: the circuit will not work if a common silicon diode like the 1N4148 is used in its place.

Parts :

R1,R7__________220R  1/4W Resistors
R2_____________120K  1/4W Resistor
R3_______________5K6 1/4W Resistor
R4_______________5K  1/2W Trimmer Cermet or Carbon
R5______________33K  1/4W Resistor
R6_____________680K  1/4W Resistor
R8_____________100K  1/4W Resistor
R9_____________180R  1/4W Resistor
C1,C2____________4µ7  25V Electrolytic Capacitors
D1____________BAT46  100V 150mA Schottky-barrier Diode
D2______________LED  Red 5mm.
Q1____________BC547   45V 100mA NPN Transistor
Q2____________BC557   45V 100mA PNP Transistor
B1_______________5V to 12V Battery supply
Notes :

• Mean current drawing of the circuit can be reduced further on by raising R1, R7 and R9 values. 

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LED Power Meter

LED power Meter circuit is a simple RF detector using diodes to charge a capacitor. The voltage developed across the capacitor is indicated by a multimeter set to a low voltage range. The circuit is soldered together without the need for a PC board, as can be seen in the diagram below and paper clips are used for the positive and negative terminals of the multimeter.

The level power output of an FM transmitter is indicated by the illumination of a LED and the voltage reading on the multimeter gives a further indication of the output.

A digital multimeter may be used but the presence of RF may produce a false reading. Likewise, the radiated energy may upset some analogue meters and you may get full scale deflection on the 15v range as well as the 250v range! But the LED wont lie. It will accurately indicate the RF and you can see the change in brightness as you adjust the coils in the output stage. Some of the cheapest and simplest multimeters will give the best results as they have a low sensitivity and the radiated RF energy will not induce a reading. Even a damaged multimeter can be used, provided the 10v or 15v DC scale is operating.

The reading is not calibrated and does not represent milliwatts output. It is only a visual indication. 

We have designed over 10 FM transmitters for inclusion in the pages of this e-magazine and each one has different features and characteristics. Some are designed for 3v operation, some are for 9v operation, some are stable for hand-held situations and others are designed for high output. The illumination of the LED will range from barely visible to very bright. 

LED Power Meter Parts 

1 - 470R

1 - 100p ceramic

1 - 100n ceramic

2 - 1N 4148 diodes

1 - 5mm Red LED

1 - 2in (5cm) hook-up wire

2 - paper clips

No PC board required

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Constant Current LED Driver Circuit

 If an LED is used in a circuit, the current for that LED is normally set with a limiting resistor. The LED can then be switched on and off by means of a transistor.
The following discussions explains a transistor based configuration which ensures a constant current drive to the conected LEDs, under  all circumstance.

However, the method shown in figure l does not take into account any variations in the supply voltage. A small variation in the LED current can be very conspicuous especially when high efficiency LEDs are used. The addition of just one transistor can transform the circuit of figure 1 to a onstant current source which can be switched on an off (for instance, with TTL levels). The circuit of figure 2 shows that resistor R1 has been moved to the emitter of T1. When a drive voltage is applied to the input of T1, this transistor conducts which causes a current through R1. Transistor T2 controls the base current of T1 such that I the voltage drop across R1 remains at 0.6 V. The current, l, through the LEDs and R1 is calculated by l= 0.6/R1. lf, for instance, R1 is 12 S2, the current through the LEDs is 50 mA. Bear in mind that the dissipation of T1 is somewhat higher than in the circuit of figure 1, but against that, the dissipation in R1 is not as high.

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LED Indicator Relay Timer Circuit 9 Second

This Relay Timer circuit provides a visual time 9 second delay using ten LED before control by closing a 12 VDC relay. That the reset switch has closed, IC 4017 decade counter will be reset to zero count which illuminates the LED driven from pin 3.

IC 555 timer output at pin 3 will be high and the voltage at pins 6 and 2 of the timer will be a little less than the lower trigger point, or about 3 Vdc.

That time the switch is opened, the transistor in parallel with the timing capacitor (22uF) is shut off allowing the capacitor to begin charging and the IC 555 timer circuit to produce an approximate one second clock signal to the decade counter. The counter advances on each positive going change at pin 14 and is enabled with pin 13 terminated low. When the 9th count is reached, pin 11 and 13 will be high, stopping the counter and energizing the relay. Longer delay times can be obtained with mostcapacitor or most resistor at pins 2 and 6 of the IC 555 timer

Source: 9 Sec Timer with LED indication and Control Relay Circuit

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PHILCO PHILIPS PH32S86DG – LED LCD TV POWER SUPPLY REGULATOR and AUDIO OUTPUT SCHEMATIC

Power Supply Regulator Circuit & Audio Output schema_ PHILCO [PHILIPS] PH32S86DG – LED LCD TV 

ICs used [TPA3020 (Audio Output) – D7537R (Power Control)

SMPS SCHEMATIC

AUDIO OUTPUT SCHEMATIC

CLICK ON THE SCHEMATICS TO MAGNIFY

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LED 4 Channel Commutator Wiring diagram Schematic

This is a simple LED 4-Channel Commutator Circuit Diagram.The DS7800 voltage translator is a monolithic device that provides from 10 V to -20 V gate drive to the JFETs while at the same time providing DTL/TTL logic compatibility.

LED 4-Channel Commutator Circuit Diagram

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Blinking LED Wiring diagram Schematic

This is a blinking LED schema diagram.Here I have used common IC NE555.If you want to change the speed of this schema you can change the value of R2.Then you can do that.







Note

* Use a PCB to build this schema
* You can operate this schema with 9V Read More