0 Fastest Finger First Indicator

Quiz-type game shows are increasingly becoming popular on tale vision these days. In such games, fastest finger first indicators (FFFIs) are used to test the player’s reaction time. The player’s designated number is dis played with an audio alarm when the player presses his entry button. The circuit presented here determines as to which of the four contestants first pressed the button and locks out the remaining three entries. Simultaneously, an audio alarm and the correct decimal number display of the corresponding contestant are activated. 

Fastest Finger First Indicator Circuit Diagram:

 

Fastest Finger First Indicator Circuit Diagram

 

When a contestant presses his switch, the corresponding output of latch IC2 (7475) changes its logic state from 1 to 0. The combinational circuitry comprising dual 4-input NAND gates of IC3 (7420) locks out subsequent entries by producing the appropriate latch-disable signal. Priority encoder IC4 (74147) encodes the active-low input condition into the cor responding binary coded decimal (BCD) number output. The outputs of IC4 after inversion by inverter gates inside hex inverter 74LS04 (IC5) are coupled to BCD-to-7-segment decoder/display driver IC6 (7447). The output of IC6 drives common-anode 7-segment LED display (DIS.1, FND507 or LT543). 

The audio alarm generator comprises clock oscillator IC7 (555), whose output drives a loudspeaker. The oscillator frequency can be varied with the help of preset VR1. Logic 0 state at one of the outputs of IC2 produces logic 1 input condition at pin 4 of IC7, thereby enabling the audio oscillator.  IC7 needs +12V DC supply for sufficient alarm level. The remaining circuit operates on regulated +5V DC supply, which is obtained using IC1 (7805). Once the organiser identifies the contestant who pressed the switch first, he disables the audio alarm and at the same time forces the digital display to ‘0’ by pressing reset pushbutton S5. With a slight modification, this circuit can accommodate more than four contestants. 

Author : P. Rajesh Bhat  – Copyright : EFY

Detail: Fastest Finger First Indicator

0 Modem Off Indicator

The modem off indicator is intended especially for serious Internet surfers. It will be seen that the circuit of the indicator cannot be much simpler, or there might be nothing left. In spite of its simplicity, it may prove to be a cost-saving device, since it shows at a glance whether the telephone line is free again after the modem has been used. This obviates high telephone charges in case for some reason the modem continues to operate. The circuit depends on the fact that there is a potential of about 40 V on the telephone line when it is not busy. This voltage drops sharply when a telephone call is being made. If, therefore, the circuit is linked to telephone terminals a and b, the lighting of the green LED shows that the line is not busy in error.

Modem Off Indicator Circuit diagram:

 Modem Off Indicator Circuit Diagram

The bridge rectifier ensures that the polarity of the line voltage is of no consequence. This has the additional benefit that polarity protection for the LED is not necessary. To make sure that the telephone line is not loaded unnecessarily, the LED is a high efficiency type. This type lights at a current as low as 2 mA, and this is, therefore the current arranged through it by resistor R1.

WARNING.

In spite of the liberal age we live in, it is highly probable that in many countries it is not allowed to connect the indicator across the telephone lines. Seek advice of your local telephone company that owns or operates the telephone network.

Detail: Modem Off Indicator

0 Power On Indicator

Some types of electronic equipment do  not provide any indication that they are  actually on when they are switched on.  This situation can occur when the back-light of a display is switched off. In addition, the otherwise mandatory mains  power  indicator  is  not  required  with  equipment  that  consumes  less  than  10 watts. As a result, you can easily forget  to switch off such equipment. If you want  to know whether equipment is still drawing power from the mains, or if you want  to have an indication that the equipment  is switched on without having to modify the equipment, this circuit provides a solution. 

One way to detect AC power current and  generate a reasonably constant voltage  independent of the load is to connect a  string of diodes wired in reverse parallel in series with one of the AC supply  leads. Here we selected diodes rated  at 6 A that can handle a non-repetitive  peak current of 200 A. The peak current  rating is important in connection with  switch-on  currents.  An  advantage  of  the selected diodes is that their voltage  drop increases at high currents (to 1.2 V  at 6 A). This means that you can roughly  estimate the power consumption from  the brightness of the LED (at very low  power levels). The voltage across the diodes serves as  the supply voltage for the LED driver. To  increase the sensitivity of the circuit, a  cascade circuit (voltage doubler) consisting of C1, D7, D8 and C2 is used to double  the voltage from D1–D6. Another benefit  of this arrangement is that both halve- waves of the AC current are used. We use  Schottky diodes in the cascade circuit to  minimise the voltage losses. 

Power On Indicator Circuit diagram :
 

Power On Indicator Circuit Diagram

The LED driver is designed to operate the LED  in blinking mode. This increases the amount  of current that can flow though the LED when  it is on, so the brightness is adequate even  with small loads. We chose a duty cycle of pproximately 5 seconds off and 0.5 second  on. If we assume a current of 2 mA for good  brightness with a low-current LED and we can  tolerate a 1-V drop in the supply voltage, the  smoothing capacitor (C2) must have a value of  1000 µF. We use an astable multivibrator built around two transistors to implement a  high-efficiency LED flasher. It is dimensioned to minimise the drive current of  the transistors. The average current consumption is approximately 0.5 mA with a  supply voltage of 3 V (2.7 mA when the  LED is on; 0.2 mA when it is off). C4 and  R4 determine the on time of the LED (0.5  to 0.6 s, depending on the supply volt-age). The LED off time is determined by  C3 and R3 and is slightly less than 5 seconds. The theoretical value is R × C × ln2,  but the actual value differs slightly due to  the low supply voltage and the selected  component values.

 

Diodes D1-D6 do not have to be special  high-voltage diodes; the reverse volt-age is only a couple of volts here due  the reverse-parallel arrangement. This  voltage drop is negligible compared to  the value of the mains voltage. The only  thing you have to pay attention to is the  maximum load. Diodes with a higher  current rating must be used above 1 kW.  In addition, the diodes may require cool-ing at such high power levels.  Measurements on D1–D6 indicate that  the voltage drop across each diode is  approximately 0.4 V at a current of 1 mA.  Our aim was to have the circuit give a  reasonable indication at current levels  of 1 mA and higher, and we succeeded  nicely. However, it is essential to use a  good low-current LED.

 

Caution: the entire circuit is at AC power potential. Never work on the circuit with the mains cable plugged in. The  best enclosure for the circuit is a small,  translucent box with the same colour as  the LED. Use reliable strain reliefs for the  mains cables entering and leaving the  box (connected to a junction box, for  example). The LED insulation does not  meet the requirements of any defined insulation class, so it must be fitted such that it  cannot be touched, which means it cannot  protrude from the enclosure.

Detail: Power On Indicator

0 Audio Clipping Indicator

Detects clipping in preamp stages, mixers, amplifiers etc., Single LED display - 9V Battery supply unit

This circuit was intended to be used as a separate, portable unit, to signal by means of a LED when the output wave form of a particular audio stage is "clipping" i.e. is reaching the onset of its maximum permitted peak-to-peak voltage value before an overload is occurring. This will help the operator in preventing severe, audible distortion to be generated through the audio equipment chain. 

This unit is particularly useful in signaling overload of the input stages in mixers, PA or musical instruments amplification chains, but is also suited to power amplifiers. A careful setting of Trimmer R5 will allow triggering of the LED with a wide range of peak-to-peak input voltages, in order to suit different requirements. Unfortunately, an oscilloscope and a sine wave frequency generator are required to accurately setup this circuit. Obviously, the unit can be embedded into an existing mixer, preamp or power amplifier, and powered by the internal supply rails in the 9 - 30V range. The power supply can also be obtained from higher voltage rails provided suitable R/C cells are inserted. SW1 and B1 must obviously be omitted.

Audio Clipping Indicator Circuit diagram:

Audio Clipping Indicator Circuit Diagram 

Parts:
R1___________1M 1/4W Resistor (See Notes)
R2,R3,R8_____100K 1/4W Resistors
R4,R6________10K 1/4W Resistors
R5___________5K 1/2W Trimmer Cermet or Carbon
R7___________2K2 1/4W Resistor
R9___________22K 1/4W Resistor
R10__________1K 1/4W Resistor (See Notes)
C1,C4________220nF 63V Polyester Capacitors
C2___________4p7 63V Ceramic Capacitor (See Notes)
C3___________220µF 25V Electrolytic Capacitor
C5___________10µF 25V Electrolytic Capacitor (See Notes)
D1,D2________1N4148 75V 150mA Diodes
D3___________LED (Any dimension, shape and color)
Q1___________BC547 45V 100mA NPN Transistor
IC1___________TL062 Dual Low current BIFET Op-Amp (or TL072, TL082)
SW1__________SPST Toggle or Slide Switch (See Text)
B1____________9V PP3 Battery (See Text)

Circuit operation:

The heart of the circuit is a window comparator formed by two op-amps packaged into IC1. This technique allows to detect precisely and symmetrically either the positive or negative peak value reached by the monitored signal. The op-amps outputs are mixed by D1 and D2, smoothed by C4, R7 and R8, and feed the LED driver Q1 with a positive pulse. C5 adds a small output delay in order to allow detection of very short peaks.

Notes:

• With the values shown, the circuit can be easily set up to detect sine wave clipping from less than 1V to 30V peak-to-peak (i.e. 15W into 8 Ohms). If you need to detect higher output peak-to-peak voltages, R1 value must be raised. On the contrary, if the circuit will be used to detect only very low peak-to-peak voltages, it is convenient to lower R1 value to, say, 220K omitting C2. In this way, the adjustment of R5 will be made easier.
• Using a TL062 chip at 9V supply, stand-by current drawing is about 1.5mA and less than 10mA when the LED illuminates. With TL072 or TL082 chips, current drawing is about 4.5mA and 13mA respectively.
• When using power supplies higher than 12V, the value of R10 must be raised accordingly.
• When using power supplies higher than 25V, the working voltage value of C5 must be raised to 35 or 50V.

Detail: Audio Clipping Indicator

0 Bridge-Rectifier LED Indicator

Using a few diodes and a LED, you can make a nice indicator as shown in associated schematic diagram that can be used for a lot of applications (with a bit of luck). It’s quite suitable for use in series with a doorbell or thermostat (but don’t try to use it with an electronically con-trolled central-heating boiler!). This approach allows you to make an attractive indicator for just a few pennies.

The AC or DC current through the circuit causes a voltage drop across the diodes that is just enough to light the LED. As the voltage is a bit on the low side, old-fashioned red LEDs are the most suitable for this purpose. Yellow and green LEDs require a somewhat higher forward voltage, so you’ll have to first check whether it works with them. Blue and white LEDs are not suitable. You also don’t have to use modern high-efficiency types (sometimes called ‘2-mA LEDs’ or ‘3-mA LEDs’). If a DC current flows through the circuit and the LED doesn’t light up, reverse the plus and minus leads.

Bridge-Rectifier LED Indicator Circuit diagram :

Bridge-Rectifier  LED Indicator Circuit Diagram

When building the circuit, you’ll notice that despite its simplicity it involves fitting quite a few components to a

small printed circuit board or a bit of prototyping board. That’s why we’d like to give you the tip of using a bridge rectifier, since that allows everything to be made much more compact, smaller and more tidy, and it eliminates the need for a circuit board to hold the components. Besides that, you can surprise friend and foe alike, because even an old hand in the trade won’t understand the trick at first glance and will likely mumble something like “Huh?

That’s impossible.”

A bridge rectifier contains four diodes, which is exactly what you need. If you short the + and – terminals of the bridge, you create a circuit with two pairs of diodes connected in parallel with oppo-site polarity. Select a bridge rectifier that can handle the current that will flow through it. In the case of a doorbell, for example, that can easily be 1 A. Select a voltage of 40 or 80 V.

Never use this circuit in combination with mains voltage, due to the risk of contact with a live lead. 

Detail: Bridge-Rectifier LED Indicator

0 Remote Audio Level Indicator

The normal level-indicator circuits which are available in the market require connections to be made to the output of the player, which may not be easily accessible. The audio level indicator circuit described here removes this restriction as it may be placed close to the player’s speakers and yet the desired effect can be realised. 

Remote Audio Level Indicator Circuit diagram :

Remote Audio Level Indicator Circuit Diagram

As shown in the circuit, signals are picked up by the condenser microphone, which get further amplified by the noninverting amplifier built around one of the four op-amps of LM324. The remaining three, along with four op-amps of the second LM324, are used as seven comparators to work as the level detector, giving seven output levels through seven coloured LEDs. 

The sensitivity of the audio level indicator circuit may be improved by varying the 220k potentiometer. If a fine adjustment is desired, a 4.7-kilohm potentiometer may be connected in series resistors with the 220k potentiometer.

Copyright : EFY

Detail: Remote Audio Level Indicator

0 Maximum Minimum Voltage Indicator

This circuit indicates which of three voltages in the range from about about -4V to about +4V - at A, B and C - is the highest by lighting one of three indicator LEDs. Alternatively, it can be wired to indicate the lowest of three voltages or to indicate both the highest and lowest voltages. Op amps IC1a, IC1b & IC1c are wired as comparators, while the three indicator LEDs and their series 1kO current limiting resistors are strung across the op amp outputs to implement the appropriate logic functions.

Maximum Minimum Voltage Indicator Circuit diagram:

 Maximum Minimum Voltage Indicator Circuit Diagram

For example, LED A will light only when pin 8 of IC1c is low (ie, A greater B) and pin 7 of IC1b is high (ie, A greater C). Similarly, LED B will light only when pin 8 of IC1c is high (ie, B greater A) and pin 1 of IC1a is low (ie, B greater C). LED C works in similar fashion if the voltage at C is the highest. Note that if all the LEDs and their parallel 1N4148 diodes are reversed, the circuit will indicate the lowest of the three input voltages. And if each 1N4148 diode is replaced by a LED, the circuit will indicate both the highest and lowest inputs.

Author: Andrew Partridge - Copyright: Silicon Chip

Detail: Maximum Minimum Voltage Indicator

0 Supply Voltage Indicator

A novel supply voltage monitor which uses a LED to show the status of a power supply. This simple and slightly odd circuit can clearly show the level of the supply voltage (in a larger device): as long as the indicator has good 12 volts at its input, LED1 gives steady, uninterrupted (for the naked eye) yellow light. If the input voltage falls below 11 V, LED1 will start to blink and the blinking will just get slower and slower if the voltage drops further - giving very clear and intuitive representation of the supply's status. The blinking will stop and LED1 will finally go out at a little below 9 volts. On the other hand, if the input voltage rises to 13 V, LED2 will start to glow, getting at almost full power at 14 V. The characteristic voltages can be adjusted primarily by adjusting the values of R1 and R4. The base-emitter diode of T2 basically just stands in for a zener diode.

Supply Voltage Indicator Circuit diagram:

Supply Voltage Indicator Circuit Diagram

The emitter-collector path of T1 is inversely polarized and if the input voltage is high enough - T1 will cause oscillations and the frequency will be proportional to the input voltage. The relaxation oscillator ceases cycling when the input voltage gets so low that it no longer can cause breakdown along the emitter-collector path. Not all small NPN transistors show this kind of behavior when inversely polarized in a similar manner, but many do. BC337-40 can start oscillations at a relatively low voltage, other types generally require a volt or two more. If experimenting, be careful not to punch a hole through the device under test: they oscillate at 9-12 V or not at all.

Detail: Supply Voltage Indicator

0 Clipping Indicator For Audio Amplifiers

A clipping indicator is a useful accessory on any audio amplifier. It indicates when the amplifier has reached its limit and is clipping the peaks of the audio signal. In practice, quite a lot of clipping can occur before you can hear it. So why is it necessary to know when an amplifier is clipping if you can't notice it? The answer is that clipping "squares up" the waveform and square waves contain lots of higher-frequency harmonics which can easily damage the tweeters in loudspeaker systems. This circuit is a true clipping indicator as opposed to the level indicators that are commonly used in preamplifier stages.

The problem with level indicators is that an amplifier's maximum output power is not constant. That's because the amplifier's supply rails are not regulated and so the maximum power available at any given instant varies, depending on the applied signal. The circuit is quite simple and is based on two BD140 PNP transistors and zener diode ZD1. During normal operation, Q1 is turned on via ZD1 and R1. As a result, Q2 is held off (since its base is pulled high) and so LED1 is also off. However, if the output signal subsequently rises to within 4.7V of the positive supply rail, Q1 turns off since it no longer has any forward bias on its base.

Clipping Indicator For Audio Amplifiers Circuit diagram:

Clipping Indicator Circuit Diagram

As a result Q2's base is now pulled low via R2 and so Q2 turns on and lights LED1. (Note: the 0.6V drop across Q1's base/emitter is ignored here because ZD1 conducts before its rated voltage due to the very low current involved). Why choose 4.7V below the power rail as the turn-on point? The reason is that, due to the drive limitations and the nature of emitter followers, they can be expected to have at least 4V across them when they saturate (ie, clip). ZD1 can be increased to a 5V or 6.2V type if the circuit is to be used with a monster amplifier.

The value of R3 should be customized according to the amplifier's supply rail, so that LED1 operates with the correct brightness. To do that, first measure the amplifier's positive supply voltage, then use Ohms Law (R = V/I) to calculate the value of R3 for a current of about 20mA. As it stands, this circuit can only be used to monitor the positive-going half-cycles of the audio waveform. If you want to monitor the negative half-cycles as well, you will have to build a second circuit with the following changes: (1) reverse both LED1 and ZD1; and (2) use BD139 (NPN) transistors for Q1 & Q2. Note that, in both cases, you should use the earth inside the amplifier, as the speaker negative may not be earth (such as in a bridged output).

Author: Philip Chugg - Copyright: Silicon Chip Electronics Magazine

Detail: Clipping Indicator For Audio Amplifiers

0 110 and 220V AC LED Voltage Indicator

Useful for power lines control, Simple, transformer less circuitry. This circuit, designed on request, has proven to be useful to indicate when the voltage in a power supply line is changing from 120V to 240Vac. It can be used in different circumstances and circuits, mainly when an increase in ac or dc supply voltage needs to be detected. D3 illuminates when the line voltage is approaching 120V and will remain in the on state also at 240V supply. On the other hand, D6 will illuminate only when the line voltage is about 240V and will stay on because the latching action of Q1, Q2 and related components. C1, D1 and D2 provide a low dc voltage in the 4.5V - 6V range in order to allow proper operation of latch circuit and LEDs.

110 and 220V AC LED Voltage Indicator Circuit diagram:

110 and 220V AC LED Voltage Indicator Circuit Diagram

Parts:
R1__________470R 1/2W Resistor
R2__________220K 1/4W Resistor
R3,R7_______470R 1/4W Resistors
R4__________1K 1/4W Resistor
R5__________2K2 1/4W Resistor
R6_________330R 1/4W Resistor
C1_________330nF 630V Polyester Capacitor
C2_________10µF 25V Electrolytic Capacitor
D1,D2______N4007 1000V 1A Diode
D3,D6______LEDs (Color and shape at will)
D4_________BZX79C10 10V 500mW Zener Diode (See Notes)
D5_________1N4148 75V 150mA Diode
Q1_________BC547 45V 100mA NPN Transistor
Q2_________BC557 45V 100mA PNP Transistor

Notes:

• D4 value could require some adjustment in order to allow precise switching of the circuit at the chosen voltage. If the case, please try values in the 8.2V - 15V range.
• Warning! The circuit is connected to 240Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.

Detail: 110 and 220V AC LED Voltage Indicator

0 Water Level Indicator Circuit

Simple, two-wire, remote monitoring unit, Three-LED level display, 9V battery powered. The whole project was developed on a friend's request. Its purpose was to remotely monitor the water-level in a metal tank located in the attic by means of a very simple control unit placed in the kitchen, some floors below.

Mains requirements were:

1. No separate supply for the remote circuit
2. Main and remote units connected by a thin two-wire cable
3. Simple LED display for the main unit
4. Battery operation to avoid problems related to mains supply and water proximity
5. As the circuit was battery operated a low current consumption was obviously welcomed

The very small remote unit is placed near the tank and measures the water level in three ranges by means of two steel rods. Each range will cover one third of the tank capacity:

• Almost empty - signaled by means of a red LED (D3) in the control unit display
• About half-level - signaled by means of a yellow LED (D2) in the control unit display
• Almost full - signaled by means of a green LED (D1) in the control unit displa

Circuit diagram:

Water-level Indicator Circuit Diagram

Circuit operation:

When the water-level is below the steel rods, no contact is occurring from the metal can and the rods, which are supported by a small insulated (wooden) board. The small circuit built around IC1 draws no current and therefore no voltage drop is generated across R5. IC2A, IC2B and Q1 are wired as a window comparator and, as there is zero voltage at input pins #2 and #5, D3 will illuminate. When the water comes in contact with the first rod, pin #13 of IC1 will go high, as its input pins #9 to #12 were shorted to negative by means of the water contact. Therefore, R4 will be connected across the full supply voltage and the remote circuit will draw a current of about 9mA. 

This current will cause a voltage drop of about 0.9V across R5 and the window comparator will detect this voltage and will change its state, switching off D3 and illuminating D2. When the water will reach the second rod, also pin #1 of IC1 will go high for the same reason explained above. Now either R3 and R4 will be connected across the full supply voltage and the total current drawing of the remote circuit will be about 18mA. The voltage drop across R5 will be now about 1.8V and the window comparator will switch off D2 and will drive D1. The battery will last very long because the circuit will be mostly in the off state. Current is needed only for a few seconds when P1 is pushed to check the water-level and one of the LEDs illuminates.

Parts:

R1 = 15K 1/4W Resistors
R2 = 15K 1/4W Resistors
R3 = 1K 1/4W Resistors
R4 = 1K 1/4W Resistors
R5 = 100R 1/4W Resistor
R6 = 47K 1/4W Resistor
R7 = 3.3K 1/4W Resistors
R8 = 3.3K 1/4W Resistors
R9 = 2.7K 1/4W Resistors
R10 = 15K 1/4W Resistors
R12 = 15K 1/4W Resistors
R13 = 3.3K 1/4W Resistors
R14 = 2.7K 1/4W Resistors
R15 = 2.7K 1/4W Resistors
D1 = 3mm Green LED
D2 = 3mm Yellow LED
D3 = 3mm Red LED
C1 = 470nF 63V Polyester or Ceramic Capacitor
J1 = Two ways output sockets
J2 = Two ways output sockets
P1 = SPST pushbutton
B1 = 9V PP3 Battery
Q1 = BC547 45V 100mA NPN Transistor
IC1 = 4012 Dual 4 input NAND gate IC
IC2 = LM393 Dual Comparator IC
Two steel rods of appropriate length

Notes:

• The two steel rods must be supported by a small insulated (wooden) board
• IC1 and R1-R4 are mounted on a small board placed near or on the steel rods support
• The two-wire cable connecting the remote circuit board to the main control board, i.e. J1 to J2, can be of any size and type (preferably thin for obvious reasons). It can be very long, if necessary.
• The circuit can be used also with non-metal tanks, provided a third steel rod having the height of the tank will be added and connected to pin #7 of IC1, R3, R4 and J1.
• The 4012 chip was chosen because it contains two gates and was at hand, but you can use two of the gates contained into 4001, 4011, 4093, 4049, 4069 etc. chips, provided all inputs of each gate are tied together and all inputs of unused gates are connected to the positive rail, leaving output pins open.

Detail: Water Level Indicator Circuit

0 Yes-No Indicator Has Zero Standby Current

This circuit produces a random "Yes" or "No" with a single button press - indicated by the illumination of a red or green LED. The circuit has two advantages over similar circuits. First, it uses just a single momentary contact pushbutton, so no on-off switch is required. When the pushbutton is pressed, an oscillator comprising the 10nF capacitor and 22kΩ resistor at pins 1 & 2 is almost immediately stopped by FET Q1, which pulls the oscillator's timing capacitor to the positive rail. However, the 220nF capacitor and 470kΩ resistor in the gate circuit of Q1 introduce a tenth of a second's delay, so that about 250 oscillations take place before the clock is stopped.

Due to variations in charge on the circuit's capacitors, as well as voltage and temperature variations, and the unpredictability of when the pushbutton will be pressed, randomness is assured. The circuit has a high degree of randomness because it takes advantage of a near-perfect complementary square waveform at pins 10 and 11 of the 4047 IC. The oscillator frequency (available at pin 13) is passed through an internal divide-by-2 circuit in the 4047. This appears at pin 10 (Q), and is inverted at pin 11 (Q-bar), thus assuring a near perfect 50:50 duty cycle for the two LEDs.

Yes-No Indicator Has Zero Standby Current Circuit diagram:

Yes-No Indicator Circuit Diagram

Note:
However, that the "impartiality" of the circuit is partly contingent on the value of the 10nF capacitor and on a reasonably equal current flow through both LEDs. Over five trials, the Yes-No Indicator scored 142 Yes, 158 No, with Yes falling behind No in the fourth trial. Because the circuit only works while switch S1 is pressed, standby current is zero, therefore a miniature 12V battery may be used to power it. In this case the circuit could be used thousands of times before the battery would run flat. The circuit has a further potential use. If the LEDs are omitted and a piezo (capacitive) sounder is wired directly to pins 10 and 11, it will produce a loud beep when equipment is turned on, and will continue to draw less than 0.5mA until it is switched off. The frequency of the beep may be changed by altering the value of the 10nF capacitor and its duration by altering the value of the 220nF capacitor.

Author: Thomas Scarborough - Copyright: Silicon Chip Electronics

Detail: Yes-No Indicator Has Zero Standby Current

0 Digital Mains Voltage Indicator

Continuous monitoring of the mains voltage is required in many ap-plications such as manual volt-age stabilisers and motor pumps. An ana-logue voltmeter, though cheap, has many disadvantages as it has moving parts and is sensitive to vibrations. The solidstate voltmeter circuit described here indicates the mains voltage with a resolution that is comparable to that of a general-pur-pose analogue voltmeter. The status of the mains voltage is available in the form of an LED bar graph. Presets VR1 through VR16 are used to set the DC voltages corresponding to the 16 voltage levels over the 50-250V range as marked on LED1 through LED16, respectively, in the figure. The LED bar graph is multiplexed from the bottom to the top with the help of ICs CD4067B (16-channel multiplexer) and CD4029B (counter). The counter clocked by NE555 timer-based astable multivibrator generates 4-bit binary ad-dress for multiplexer-demultiplexer pair of CD4067B and CD4514B. 

Digital Mains Voltage Indicator Circuit diagram:

Digital Mains Voltage Indicator Circuit Diagram

The voltage from the wipers of pre-sets are multiplexed by CD4067B and the output from pin 1 of CD4067B is fed to the non-inverting input of comparator A2 (half of op-amp LM358) after being buff-ered by A1 (the other half of IC2). The unregulated voltage sensed from rectifier output is fed to the inverting input of com-parator A2. The output of comparator A2 is low until the sensed voltage is greater than the reference input applied at the non-inverting pins of comparator A2 via buffer A1. When the sensed voltage goes below the reference voltage, the output of com-parator A2 goes high. The high output from comparator A2 inhibits the decoder (CD4514) that is used to decode the out-put of IC4029 and drive the LEDs. This ensures that the LEDs of the bar graph are ‘on’ up to the sensed voltage-level pro-portional to the mains voltage.

The initial adjustment of each of the presets can be done by feeding a known AC voltage through an auto-transform and then adjusting the corresponding pre-set to ensure that only those LEDs that are up to the applied voltage glow. 

EFY note.  It is advisable to use ad-ditional transformer, rectifier, filter, and regulator arrangements for obtaining a regulated supply for the functioning of the circuit so that performance of the cir-cuit is not affected even when the mains voltage falls as low as 50V or goes as high as 280V. During Lab testing regu-lated 12-volt supply for circuit operation was used.)

Author : Pratap Chandra Sahu - Copyright : EFY

Detail: Digital Mains Voltage Indicator

0 2-Pin Automobile Indicator Lamp Flasher Circuit with Buzzer

If you want to make a flasher unit for you motorbike then this circuit is just for you. This simple turn signal flasher circuit can be  easily built and installed in any two wheelers for the desired actions. The circuit employs just two 2-pins instead of 3 as found in other flasher circuits. Once installed, the circuit will faithfully flash the side indicator lights whenever the intended function is switched ON. The circuit also incorporates an optional buzzer circuit which can be also included for getting a beeping sound in response to the flashing of the lamps.


.

Parts List

R1, R2, R3 = 10K

R4= 33K

T1 = D1351,

T2 = BC547,

T3 = BC557,

C1, C2 = 33uF.25V

L1 = Buzzer Coil

Detail: 2-Pin Automobile Indicator Lamp Flasher Circuit with Buzzer

0 Simple Indicator for Dynamic Limiter Schematic Diagram

The indicator described here is specifically designed for adjusting the dynamic limiter described elsewhere in this edition and checking whether the maximum level of the reference voltage (P1) needs to be modified. Her e we use a 4 -to -16 decoder IC (type 4514) to monitor the state of the four-bit up/down counter in the limiter circuit. This IC can be powered from the ±8 V supply voltages of the limiter. The limiter board has a 6-way connector (K5) that provides access to the four counter outputs and the sup-ply voltages. Connector K1 of the indicator circuit can be connected to K5 on the limiter board.
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 Indicator for Dynamic Limiter Schematic

One output of the 4514 goes high for each unique 4-bit combination on its inputs, while the other outputs remain logic Low. A separate current-limiting resistor is connected in series with each LED. It was not possible to use a common cathode resistor here because most LEDs have a maximum reverse blocking voltage of only 5 V, while the supply voltage here (16 V) is a good deal higher.

The 16 LEDs ar ranged in a r ow pr ov ide a ‘fluid’ indication of the control process. You can enhance the display by using different colours for the first and last LEDs, such as red for D1 (maximum gain) and green for D16 (minimum gain), with yellow for the rest of the LEDs. While observing signals from various sources (TV set, DVD, media player, etc.), you can easily use the 16 LEDS to monitor the behaviour of the limiter and adjust the setting of potentiometer P1 in the limiter circuit. It must be set such that D16 only lights up at the maximum signal level. If this is not possible and D16 remains lit a good deal of the time regardless of the position of P1, it will be necessar y to increase the value of P1. Of course, it is also poss-ible to adjust P1 so the strongest signal source extends slightly above the control range of the limiter.

This circuit can easily be assembled on a small piece of prototyping board. The current consumption is around 4 mA. link

Detail: Simple Indicator for Dynamic Limiter Schematic Diagram

0 Build an AC mains voltage indicator

All three LEDs of AC mains voltage indicator are connected between collectors of transistors T1, T2, T3 respectively. Here potentiometer VR1, VR2, and VR3 are used to adjust the base voltage of transistor T1, T2 and T3 respectively. As shown in circuit diagram first AC mains is stepped down by 9V-0-9V transformer and then rectified by a signal diode D1 and smoothed by C1 which give output 25V DC. 

This circuit is work on the principle, when AC mains vary DC voltage also varies proportionally and sensed by transistor T1 through T3. For setting the low level voltage, a manual AC voltage regulator (MVR) should be connected to the primary of transformer X1. Now set AC voltage of MVR to about 175V and slowly potentiometer VR1 adjusted until voltage across the base of transistor T1 reaches 9.7V and transistor starts conducting which glow LED1 and stop glowing when the base voltage drops below the preset value. 

This process is repeated for 200V and 230V in which LED2 and LED3 glows respectively. Now connect this circuit to AC mains, if the voltage drop below 175 volts no LEDs glow. First, a high voltage (more than 230V) is indicated by all three LEDs glows (LED1, LED2, LED3). Second, normally voltage (200V-230V) is indicated by two LEDs (LED1 and LED2). Third, a low voltage (175V-200V) is indicated by the glowing of LED1 only.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁- R₆= 1 KΩ

VR₁ – VR₃ = 10 KΩ

Capacitor

C₁ = 220 µF/50V

Semiconductors

T₁ – T₃ = BC547

ZD₁ – ZD₃ = 9.1V zener diode

D₁ = 1N4001

LED₁ – LED₃ = Simple LED

Miscellaneous

X₁ = 230V AC primary to 9V-0-9V, 250mA secondary transformer

SW₁ = On/off switch

Detail: Build an AC mains voltage indicator