Electronic Fuse Employs A Relay

Many power supplies can be set to limit their output current to a defined level, to protect the circuit they are powering, no such protection is available if you are powering a circuit from a battery. If a fault develops, the circuit can blow before you have a chance to disconnect it. Of course, you can fit a fuse in series with the supply line to the circuit under test but it will blow if a fault develops. Or perhaps it won’t blow sufficiently quickly to protect the circuit. And repeatedly having to replace fuses becomes a nuisance as well.

Electronic Fuse Employs A Relay Circuit Diagram:

 
The alternative is to use an electronic fuse. This circuit uses a relay to make and break the circuit. The current drain of the circuit under test is monitored by a 1O 2W resistor which is placed in series with the supply line. The voltage across this 1O resistor is monitored by op amp IC1a which has an adjustable gain of between 11 and 16, as set by trimpot VR1. The resultant DC voltage from pin 1 of IC1a is fed to pin 5 of IC1b which is configured as a comparator. Trimpot VR2 provides an adjustable voltage reference to pin 6 of IC1b and this is compared with the amplified signal from IC1a.

If IC1b’s threshold is exceeded, its pin 7 goes high and this is fed to Schmitt trigger inverter IC2a which then “sets” the RS flipflop comprising gates IC2c & IC2d. Pin 11 of IC2d then goes high to turn on transistor Q2 and LED1 while pin 4 of IC2b also goes high to turn on Q1 and the relay which then disconnects the load. The circuit stays in this state until the RS flipflop is reset by pushing switch S1. Capacitor Cx, across the feedback resistance of IC1a, is used to simulate a slow-blow or fast-blow fuse and can be selected by trial and error. Changing the gain of IC1a or the value of the sensing resistor changes the fuse rating of the circuit.

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Relay activated by Sound

This is a Relay activated by Sound Circuit Diagram. Generally a circuit has a basic function, but according to our needs can modify or add to a circuit making it more complex. This circuit is a relay activated by sound, which can be used in an alarm system, home automation, robot and even in an Arduino. Undoubtedly this control by sound can be very useful, an example is a light activated by the sound of a knock on the door or a round of applause. 

Relay activated by Sound Circuit Diagram:

The light turns off automatically after a few seconds. An alternative is to use protection against theft - if someone wants to open the door or break something light illuminates, indicating that someone is home. The circuit can work with any voltage 5-12 Vdc, it depends on the voltage of the relay coil.

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Simple Garage Door Closing Circuit Just using Relays

Because I’m old school, I wanted to build a Garage Door Closing circuit without relying on integrated configurations (555 timer etc) to keep it simplistic. The circuit closes the garage door after two minutes with C3 and four minutes with the addition of C2. The timer relay is surprisingly accurate (+/- five seconds). Another feature is to ensure that the garage door actually did close, such as if it’s stopped mid-operation by the user.

S3 (magnetic N.C.) is located at the garage door and activates the circuit when the garage door opens.
RL1 is the reset timer. It’s maintained in the “on” position for two minutes by C3 while the trigger capacitor, C4, is charged. RL2 is the conduit, directing C4 to either RL3 or R1 to ground when off. Purpose of R1 is to prevent arching across contacts and a fast discharge. RL3’s contacts are connected to the Garage Door’s Momentary Switch and is sustained “on”  for a half second by C5.

When C3 discharges to the cutoff voltage of RL1, it turns off and resets. C4 charges C5, which turns on RL3 and initiates the garage door. Because C4 does not have the time to fully discharge, it should be at least three times the value of C5. If it does not close, RL1 in countdown mode will reset and open the door. When it resets again, the door will close.

Turning off the circuit, C1 maintains RL1 “on” slightly longer to ensure that RL2 is set to discharge C4 to R1. If this is not done and C4 is not discharged, the garage door will not open until it discharges naturally and falls below the trigger voltage for RL3.  The circuit would be useless for several days.

Notes:

• Time delay of RL1 after reset drops 15 seconds because of the short charge time.
• To boost RL3 to a one-second delay, increase C5 to 1000uF.
• D2, D3, and D4 isolate the crucial sections of the circuit.
• Relays do not turn off at the same rate. I conducted a test by tripping the circuit on and off at a high rate and discovered the possibility of C4 turning on RL3. The addition of C1 solved this.

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Relay Toggle Circuit Using a 555 Timer

Here is a simple electronic projects of relay toggle circuit with 555 timer.  This 555 timer circuit below toggles a relay when a button is pressed. Pins 2 and 6, the threshold and trigger inputs, are held at 1/2 the supply voltage by the two 10K resistors. When the output is high, the capacitor charges through the 100K resistor, and discharges when the output is low. When the button is pressed, the capacitor voltage is applied to pins 2 and 6 which causes the output to change to the opposite state.

Relay Toggle Circuit Diagram:

When the button is released, the capacitor will charge or discharge to the new level at the output (pin 3). The parts are not critical, the resistors can be somewhat higher or lower, but the 2 resistors at pins 2 and 6 should be equal values, and the resistor connected to the cap should be 10 times greater or more.

Advantages of this circuit are the large hystersis range at the input which avoids false triggering, and only a few parts are needed for construction. One disadvantage is the relay may be engaged when power is first applied. To solve this problem, you could tie the reset line (pin 4) to another resistor/capacitor combination with the capacitor at ground and the resistor at the +V point. This will cause pin 4 to be held near ground for a short period which will reset the output when power is applied.

The 100 ohm resistor and 100uF capacitor serve to filter noise on the supply line if the circuit is used in a automotive application. They may not be necessary. The circuit may work well without those parts.

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How to Build AC Line Current Detector

This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of the AC lines through an inductive pickup (L1) made with a 1 inch diameter U-bolt wound with 800 turns of #30 - #35 magnet wire. The pickup could be made from other iron type rings or transformer cores that allows enough space to pass one of the AC lines through the center. 

Only one of the current carrying lines, either the line or the neutral should be put through the center of the pickup to avoid the fields cancelling. I tested the circuit using a 2 wire extension cord which I had separated the twin wires a small distance with an exacto knife to allow the U-bolt to encircle only one wire.

AC Line Current Detector Circuit Diagram

The magnetic pickup (U-bolt) produces about 4 millivolts peak for a AC line current of 250 mA, or AC load of around 30 watts. The signal from the pickup is raised about 200 times at the output of the op-amp pin 1 which is then peak detected by the capacitor and diode connected to pin 1. The second op-amp is used as a comparator which detects a voltage rise greater than the diode drop. The minimum signal needed to cause the comparator stage output to switch positive is around 800 mV peak which corresponds to about a 30 watt load on the AC line.

The output 1458 op-amp will only swing within a couple volts of ground so a voltage divider (1K/470) is used to reduce the no-signal voltage to about 0.7 volts. An additional diode is added in series with the transistor base to ensure it turns off when the op-amp voltage is 2 volts. You may get a little bit of relay chatter if the AC load is close to the switching point so a larger load of 50 watts or more is recommended. The sensitivity could be increased by adding more turns to the pickup.

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Solid State Relay - Required Only 50uA Drive Current

This circuit demands a control current that is 100 times smaller than that needed by a typical optically isolated solid state relays. It is ideal for battery-powered systems. Using a combination of a high current TRIAC and a very sensitive low current SCR, the circuit can control about 600 watts of power to load while providing full isolation and transient protection.

Solid State Relay Circuit diagram:

 Source: Discover Circuits

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Automatic Turn Off Relay

Per request the circuit today we have relay circuit. It is worth noting again that the diagram provides a time delay of about 0.5 seconds for every microfarad in the value of capacitor C1. This permits delays of up to several minutes. If desired, the delay periods can be made variable by replacing resistor R2 with a fixed and variable resistor in series whose nominal values are approximately equal of the total value of R2 (680K).

Automatic Turn Off Relay Circuit Diagram

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Pulse Timer Control Relay Circuit with IC555

Today we would like to offers solutions for a set time for take control relay and take NO. / NC. contact to apply to control other devices . such as disable or enable the device.function of this circuit is using IC555 to determine the pulse and a resistor R1 to the period of time.

Pulse Timer Control Relay Circuit Diagram

R1       #Seconds
100k         2
220k         3
470k         6
1M           15

The increase provides more time to increase the value of the Capacitor.

Part List
R1 = 1 Meg, Preset Pot
R2 = 10K  
R3,R4 = 1K
C1 = 10uF, 16V
C2 = 0.01uF
T1 = BC547 (Gen Purp NPN)
T2 = 2N2222 (Hi Current NPN)
D1 = 1N4001 (Gen Purp Si)
IC1 = 555 (Lo-Power version)
RLA1 = Relay, 9V (amps of your choice)

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Single Transistor Relay Toggle

The circuit below requires a double pole, double throw relay in conjunction with a single transistor to allow toggling the relay with a momentary push button. One set of relay contacts is used to control the load, while the other is used to provide feedback to keep the relay activated or deactivated. Several push buttons can be wired in parallel to allow toggling the relay from different locations.

In the deactivated state, the relay contacts are arranged so the 1000 uF capacitor will charge to about 2.7 volts. When the switch is closed, the capacitor voltage is applied to the transistor base through a 560 resistor causing the transistor to turn on and activate the relay. In the activated state, the relay contacts are arranged so the 3.3K resistor and 560 ohm resistor provide a continous current to the transistor base maintaining the activated state. While in the activated state, the capacitor is allowed to discharge to zero through the 1K resistor. When the switch is again closed, the capacitor will cause the transistor base to move toward ground deactivating the relay.

Single Transistor Relay Toggle  Circuit Diagram

The circuit has three distinct advantages, it requires only a few parts, always comes up with the relay deactivated, and doesn't need any switch debouncing. However since the capacitor will begin charging as soon as the button is depressed, the button cannot remain depressed too long to avoid re-engaging the relay. This problem can be minimized with an additional resistor connected from the transistor base to ground so that the base voltage is close to 0.7 volts with the button depressed and the transistor is biased in the linear region. With the button held down, the relay coil voltage should be somewhere between the pull in and drop out voltages so that the relay will maintain the last toggled state.

This worked out to about 820 ohms for the circuit I built using a 12 volt, 120 ohm relay coil and 2N3053 transistor. Temperature changes will effect the situation but the operation is still greatly improved. I heated the transistor with a hair dryer and found that the relay will re-engage with the button held down for approximately 1 second, but this is not much of a problem under normal operation.

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Parallel Port Relay Interface

Below are three examples of controlling a relay from the PC's parallel printer port (LPT1 or LPT2). Figure A shows a solid state relay controlled by one of the parallel port data lines (D0-D7) using a 300 ohm resistor and 5 volt power source. The solid state relay will energize when a "0" is written to the data line. Figure B and C show mechanical relays controlled by two transistors. The relay in figure B is energized when a "1" is written to the data line and the relay in figure C is energized by writing a "0" to the line. In each of the three circuits, a common connection is made from the negative side of the power supply to one of the port ground pins (18-25).

Parallel Port Relay Interface  Schematic

There are three possible base addresses for the parallel port You may need to try all three base addresses to determine the correct address for the port you are using but LPT1 is usually at Hex 0378. The QBasic "OUT" command can be used to send data to the port. OUT, &H0378,0 sets D0-D7 low and OUT, &H378,255 sets D0-D7 high. The parallel port also provides four control lines (C0,C1,C2,C3) that can be set high or low by writing data to the base address+2 so if the base address is Hex 0378 then the address of the control latch would be Hex 037A. Note that three of the control bits are inverted so writing a "0" to the control latch will set C0,C1,C3 high and C2 low.

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CMOS Toggle Flip Flop Using Laser Pointer

The circuit below is similar to the one above but can be used with a laser pointer to toggle the relay rather than a push button. The IR photo transistor Q1 (Radio Shack 276-145A) or similar is connected to the set input (pin 6). The photo transistor should be shielded from direct light so that the voltage at the set input (pin 6) is less than 1 volt under ambient conditions and moves to more than 10 volts when illuminated by the laser pointer or other light source.

CMOS Toggle Flip Flop Using Laser Pointer Circuit Diagram

The reset time is about a half second using a 4.7uF cap which prevents the circuit from toggling more than once during a half second interval. The 10K resistor and diode provide a faster discharge path for the 4.7uF cap so the circuit can be retoggled in less than 1 second. The 3K resistor in series with the photo transistor may need be adjusted for best performance. The relay shown is a solid state variety to be used with lights or other resistive loads at less than 3 amps. A mechanical relay can also be used as shown in circuit above.

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Photo Sensor Control Relay

A photo or slightly activated relay normally open relay in the closed circuit / contact with the light. In this circuit, a photodiode is used to sense light. The photodiode has a high resistance in the absence of light strikes. The photodiode is connected to the reverse biased state. The only current flowing through it will be due to minority carriers.

Photo Sensor Control Relay  Circuit Diagram

When light falls on it, the minority current carriers in the wake of increasing the diode provides a low resistance. Because the voltage across the diode will not be sufficient to bias transistor Q1 and will be reset. Where there is darkness, the resistance increases photodiode and the voltage across it will be enough to move forward bias the transistor Q1 of the relay ON. The diode D2 is used as a diode to protect transistor switching transients produced relay. In this way, the load on the relay contacts can be switched on and off using light strikes the photodiode.

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Electronic Thermostat and Relay

Here is a simple thermostat circuit that can be used to control a relay and supply power to a small space heater through the relay contacts. The relay contacts should be rated above the current requirements for the heater. Temperature changes are detected by a (1.7K @ 70F) thermistor placed in series with a 5K potentiometer which produces about 50 millivolts per degree F at the input of the LM339 voltage comparator. The two 1K resistors connected to pin 7 set the reference voltage at half the supply voltage and the hysteresis range to about 3 degrees or 150 millivolts. The hysteresis range (temperature range where the relay engages and disengages) can be adjusted with the 10K resistor between pins 1 and 7. A higher value will narrow the range.

Electronic Thermostat and Relay Circuit Diagram

In operation, the series resistor is adjusted so that the relay just toggles off at the desired temperature. A three degree drop in temperature should cause the relay to toggle back on and remain on until the temperature again rises to the preset level. The relay action can be reversed so it toggles off at the lower end of the range by reversing the locations of the 5K potentiometer and thermistor. The 5.1 volt zener diode regulates the circuit voltage so that small changes in the 12 volt supply will not effect operation. The voltage across the thermistor should be half the supply or about 2.6 volts when the temperature is within the 3 degree range set by the potentiometer. Most any thermistor can be used, but the resistance should be above 1K ohm at the temperature of interest. The series resistor selected should be about twice the resistance of the thermistor so the adjustment ends up near the center of the control.

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Sound Activated Lamp-Relay Switch

This simple circuit shown int the schematic diagram actives the switch using sound. We can use this circuit for various applications, such as automatic (sound-controlled) disco light or car’s LED light show.  The Q1 amplify the audio from mic. The R1 is used to adjust the peak of signal to greater than about 0.7 volts, act as sensitivity adjuster. A certain level, the signal coming from microphone, after amplification by Q1, will trigger the SCR and light lamp I1. If we change the lamp with a relay, then we can get a sound-activated relay/switch, which can be used to control more powerful / high wattage high voltage lamps.

Sound Activated Lamp-Relay Switch Circuit Diagram

If we use a relay, place a 1N4007 diode in parallel with the relay coil to prevent the back-emf from  relay coil destroying the SCR.

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Relay Control with MOSFET IRF511

We would like ti show you the circuit is similar to the above, but uses an N-channel MOSFET, as IRF511, 540, 640, etc. instead of the NPN transistor. Smaller MOSFETs can be used, but I do not know the part numbers. I tested the circuit with a IRF640, IRF511, IRFZ34 and REP50N06. The same circuit has three advantages, but requires only a few parts, always off to the relay and do not need a switch debounce.

In operation, when the relay is deactivated, the 100uF capacitor charge up to 6 volts. When the button is pressed, is on the capacitor 6 volts at the gate MOSFET. The capacitor voltage (and gate voltage) of 6 ms should drop to 3 volts in about 200 to move enough time for relay contacts. At very slow relay, a larger capacity. With the ratification of the relay, the contacts 12 volts to the resistance produce valid 3.3K 6 volts at the gate, holding that the relay is self-sufficient. The capacitor is then discharged to zero since the relay contact 12 is connected not to the 15K resistor.

Relay Control with MOSFET IRF511 Circuit Schematic

When the button is pressed, the capacitor is zero volts to the gate of switching off the relay. There should be no problem making the button again to be the operation of relays, since the gate voltage is only about 1.8 volts when the button is pressed and the MOSFET requires approximately 3.5 volts or more are to start running. But you wait about 1 second or more between pressing a key need, capacitor time to load or unload. Two buttons are displayed, but you could have a number of more parallel to operate the relay from multiple locations

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Relay Switch Activated by Tone and Signal

The essence of the circuit is for the input of tone and signal to provide an activation for the relay switch.

• Relay – an electrically operated switch where the current flowing through the coil of the relay is creating a magnetic field which attracts a lever and changes the switch contacts, thereby making its state open or close
• BC214 – a complementary silicon planar epitaxial transistor used in AF small signal drivers and amplifiers as well as for low noise preamplifier applications due to its feature of good linearity of DC current gain
• LM741 – a general purpose single operational amplifier with features such as offset null, compensated internal frequency, voltage range with high input, good stability of temperature, and protected from short circuit

The use of relay will allow the circuit to switch from one condition to another. It can also be referred to as a form of an electrical amplifier since it is able to control an output circuit of higher power than the input circuit. There are many types of relays being used in many electronic and electrical circuits, which include solid-state relay, Buchholz relay, overload protection relay, latching relay, forced-guided contacts relay, mercury-wetted relay, contactor relay, machine tool relay, reed relay, polarized relay, and solid state contactor relay.

Circuit Diagram

The circuit created is sensitive enough to the AC signals in the input stage, where the signals are ranging above 5 mV. It will also be sensitive to react with the human voice signals having a range of frequency from 50 Hz up to 3 KHz. The human voice is a part of the human sound produced primarily by the vocal cords or vocal folds which in turn produces a voice frequency that is used for the transmission of speech.

During the absence of an input signal, the state of the 12 V relay RL1 is at OFF condition as regulated by the 10K Ohms trimmer RV1. The circuit can be made to react with its sensitivity in points A, B, & C, where a negative feedback can be placed due to the addition of band pass filter. The filter will operate only in the 1 KHz range and the circuit will only correspond at this frequency.

Parts List :

The signal and tone activated relay switch were used in a wide range of fields which includes measuring instruments, audio systems, communications equipment, and factory-automation equipment. They can also be found on telephone subscriber circuits for the polarity reversing switch, testing, and ringing functions.

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8 Channel LPT Relay Board

Specifications:
Channel Relay Board is a simple and convenient way to interface 8 relays for switching application in your project.

• Input - 12 VDC @ 336 mA
• Output - eight SPDT relay
• Relay specification - 5 A @ 230 VAC
• Trigger level - 2 ~ 5 VDC
• Berg pins for connecting power and trigger voltage
• LED on each channel indicates relay status
• Power Battery Terminal (PBT) for easy relay output and aux power connection
• Four mounting holes of 3.2 mm each
• PCB dimensions 169 mm x 72 mm

Schematic:

Parts List:

PCB:

Download this Circuit in PDF

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9 Sec Timer with LED Indication and Control Relay

The electronic 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.

9 Sec Timer with LED Indication and Control Relay Circuit Schematic
 

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 most capacitor or most resistor at pins 2 and 6 of the IC 555 timer.

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Solid State Relays Circuit with TIL111

Solid state relays are almost everywhere these days, but they are very expensive. So, your efforts to build their own salary. Especially since it’s only a few parts and circuit simple and straightforward. Solid state relay is not really at all relays. There are no “relay” is available only with electronics, connection works. It works well as a relay, you can use low voltage higher and better. “Relay” between 115/220V AC wires in place, although it was customary, the neutral conductor and leave unchanged phases and neutral.

As long as no voltage (left in picture), the phototransistor TIL111 blocks of energy, and thus is not available. To ensure that the base TIL111 is fed to the transmitter (s) through the 1M resistor. This method prevents the base of transistor BC547B will be low and remains biased ‘on’. Collector is low and the gate (g) TIC106M thyristor, which is still in the country, “off”. 4-diode bridge rectifier circuit has no power apart from a small base and collector current BC547B, which is not enough to turn over the 330-ohm resistor TIC226M triac. Current “Load”, is very small.

Solid State Relays Circuit Diagram

With an input voltage, say 5 volts, the diode in the TIL111 lights up and activates the phototransistor. The voltage drop 1MEG ohm resistor in series with 22K resistance increases demand, which block the BC547B transistor. Collector current of the fact that the AC voltage falls below a certain value, which is VA. This ensures a sufficiently large voltage drop across the resistor 330 ohms triac switches ‘on’. The voltage on triac is currently only a few volts, so that practically the whole 115/220 AC voltage on the “Upload”.

The triac is a 100nF capacitor and impedance of 47 ohms, 100nF capacitor for the 330 ohm resistor is to protect the triac to be undesirable distortions caused by small peaks. To create the possibility of this circuit with different voltages to be switched, added BF256A FET. The FET acts as a current source from the source (s) with a gate (g). This means that this FET determines the current TIL111, regardless of the input voltage (up to a certain tolerance, of course). 1N4148 diode is to protect the circuit from reverse polarity.
(Tony: TIL111 is a so-called “optical coupling” with NPN output and can be replaced with NTE3042)

Good point line, as is the separation of AC and DC voltage, so this circuit is used in many applications, about 1.5 kW, when the triac is mounted on the large size of the cooling fins. “M” appears Triac means it’s 600volt type, “D” for 400V. So be sure to go to the M-type. NTE replacement for this circuit are 600volt types which are more than sufficient for our 110/115VAC. Even if you decide to print for this circuit is enough space between the lines AC and non AC these tracks to be close.

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Light Activated Relay

This is same circuit as above with the addition of a photo resistor to trigger the flip flop instead of a push button. The bias resistor in series with photo resistor was chosen so that sufficient voltage is present at the base of the 2N3904 to supply current to the circuit in ambient lighting conditions. The circuit should toggle when the photo resistor is hit by a flashlight beam or other fast changing light source. Slow changes in light intensity will have no effect unless the light gets too bright to maintain sufficient bias for the 2N3904.

Light Activated Relay Circuit diagram :

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