Precise FM Tuning Indicator

Here is an add on circuit to your FM radio for precise tuning of stations. Usually an LED indicator is provided in FM radio to see whether the station is tuned or not. But it is difficult to see the precise tuning points since the variation in the LED brightness cannot be detected easily. This circuit solves the problem.

Precise  FM Tuning Indicator Circuit diagram :

The circuit uses the Op Amp IC CA3140 as a differential amplifier to sense the voltage level between the terminals of the tuning LED. The output of IC1 drives two LEDs one Red and one Green to indicate whether the station is precisely tuned or not. If both LEDs remain off, it indicates precise tuning. If anyone LED is on, it indicates that tuning is not precise. If both LEDs remain on, it indicates that there is no signal.

First tune the FM receiver in a station having strong signal. The tuning LED will light brilliantly. Then connect point A and B to the soldering points of the tuning LED observing polarity. Adjust VR till both the Red and Green LEDs turn off. Slowly change the tuning knob position. Any one LED will light up. So the circuit is working. Now glue the wiper of VR using adhesive to prevent its position change. Disconnect the tuning LED from the board. Now the circuit is ready to use. Power for the circuit can be obtained from the power supply of FM radio.

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Network Voltage Indicator

Using this schematic can be made a network voltage indicator electronic circuit. If the input voltage is present across the network, the optocoupler transistor is open, T1 is blocked and controlled rectifier, Th1, is in a state of conduction. Since both terminals of the piezoelectric buzzer is at the same potential, buzzer is off. If voltage disappears, the transistor T1 enters the conduction and thus makes the terminal of buzzer to be put on the ground (maintains thyristor conduction state).

Circuit Source: DIY Electronics Projects

In this situation, there is a sufficiently large potential difference across the buzzer and D5s to determine that these two elements to indicate AC power loss, both audible and visual. By pressing the reset button current is interrupted by Th1, so thyristor enter in blocking state and the other terminal of the buzzer is connected to ground.

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Bicycle Turn Signal Indicator Circuit

Since a bicycle has no effective width, normal indicator lamps placed on each side do not give a clear indication of direction when seen from a distance,  especially at night.
The bicycle turn signal indicator circuit shown is a four stage ring counter which sequentially drives four yellow lamps giving an impression of movement i.e. towards the left or right. Lamp sequencing rate can be altered by changing C1 and C2. (50uF  was found to be about right). Oscillator pulses are shaped by schmitt a trigger lC1b. The decoding and output gating are performed by ICs 3, 4, and Driver transistors O1 to 08 C3 be any low current, medium gain NPN silicon. 

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Low drop Regulator with Indicator Wiring diagram Schematic

Even today much logic is still powered from 5 volts and it then seems obvious to power the schema using a standard regulator from a rectangular 9-V battery. A disadvantage of this approach is that the capacity of a 9-V battery is rather low and the price is rather high. Even the NiMH revolution, which has resulted in considerably higher capacities of (pen-light) batteries, seems to have escaped the 9-V battery generation. It would be cheaper if 5 volts could be derived from 6 volts, for example. That would be 4 ‘normal’ cells or 5 NiMH- cells. Also the ‘old fashioned’ sealed lead- acid battery would be appropriate, or two lithium cells.

 

Low-drop Regulator with Indicator Circuit Diagram

 

Using an LP2951, such a power supply is easily realised. The LP2951 is an ever- green from National Semiconductor, which you will have encountered in numerous  Elektor Electronics designs already. This IC can deliver a maximum current of 100 mA at an input voltage of greater than 5.4 V. In addition to this particular version, there are also versions available for 3.3 and 3 V output, as well as an adjustable version.  In this design we have added a battery indicator, which also protects the battery from too deep a discharge. As soon as the IC has a problem with too low an input voltage, the ERROR output will go low and the regulator is turned off via IC2d, until a manual restart is provided with the RESET pushbutton.

 

The battery voltage is divided with a few resistors and compared with the reference voltage (1.23 V) of the regulator IC. To adapt the indicator for different voltages you only need to change the 100-k resistor. The comparator is an LP339. This is an energy-friendly version of the LM339. The LP339 consumes only 60 µA and can sink 30 mA at its output. You can also use the LM339, if you happen to have one around, but the current consumption in that case is 14 times higher (which, for that matter, is still less than 1 mA).

 

Finally, the LP2951 in the idle state, consumes about 100 µA and depend- ing on the output current to be deliv- ered, a little more. 

Source by : Streampowers

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Battery Charge Discharge Indicator Wiring diagram Schematic

This Battery Charge-Discharge Indicator Circuit Diagram monitors car battery voltage. It provides an indication of nominal supply voltage as well as low or high voltage. RV1 and RV2 adjust the point at which the red/yellow and yellow/green LEDs are on or off. For example the red LED comes on at 11V, and the green LED at 12V. The yellow LED is on between these values.

Battery Charge-Discharge Indicator Circuit Diagram

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