The electronic switch circuit was conceived for remote control of loads from a distance. We will consider the complete device of the device another time, and in this article we will discuss a simple circuit of an electronic switch based on everyone's favorite 555 timer.

The circuit consists of the timer itself, a button without fixing the transistor as an amplifier and an electromagnetic relay. In my case, a 220 Volt relay with a current of 10 Amperes was used, such can be found in uninterruptible power supplies.

Literally any medium and high power transistors can be used as a power transistor. The circuit uses a bipolar reverse conduction transistor (NPN), but I used a direct transistor (PNP), so it will be necessary to change the polarity of the transistor connection, that is, if you are going to use a forward conduction transistor, then plus power is supplied to the emitter of the transistor, when using reverse transistors conductivity, minus power is supplied to the emitter.

From direct, you can use transistors of the KT818, KT837, KT816, KT814 series or similar, from the reverse ones - KT819, KT805, KT817, KT815 and so on.

The electronic switch works in a wide range of supply voltages, personally supplied from 6 to 16 volts, everything works well.

The circuit is activated by briefly pressing the button, at this moment the transistor instantly opens, including the relay, the latter, by closing, connects the load. The load is switched off only when pressed again. Thus, the circuit plays the role of a latching switch, but unlike the latter, it works exclusively on an electronic basis.

In my case, instead of a button, an optocoupler is used, and the circuit is closed when a command from the control panel is given. The fact is that the signal to the optocoupler comes from the radio module, which was taken from chinese typewriter radio controlled. Such a system allows multiple loads to be controlled from a distance without much difficulty.

This circuit of the electronic switch always shows good operating parameters and works flawlessly - try it and see for yourself.

Diagram of a simple homemade input selector for connecting multiple signal sources to a TV. Now the country is developing with might and main digital television... As you know, to receive it, you need either a special TV with a digital radio channel, or you need to buy a digital set-top box and connect it to any TV set via the LF inputs. But, many inexpensive TVs there is only one low frequency input.

Or two. More often it happens that the LF inputs seem to be two ("scart" and "Asia"), but in reality they simply duplicate each other. In general, the low-frequency inputs became sorely lacking. In principle, stores should have some kind of "splitters" or switches for such a case, but they are not.

In any case, I have not seen simple and cheap devices in our stores. There are very expensive switches for video surveillance systems and cheap splitters, with which the outputs of the signal sources are actually connected in parallel to each other, through 75 Ot resistors. If the audio signals still somehow tolerate this, but, alas, the video, the switched off source interferes with the working one, reducing the video signal level. Synchronization is broken.

The easiest way out of the situation is to do simplest switch, for example, according to the scheme shown in Figure 1. You need nine "Asia" sockets, respectively, three white, three red and three yellow (in order to match the purpose in colors, as is customary in the equipment), another P2K type switch for four directions (one will remain empty), well, a case, as which any soap dish will do. It can be done in an hour. Connect the cable from the TV inputs to connectors X7, X8, X9.

Two more cables - to the DVD-player and digital set-top box, respectively, connectors X1, X2, X3 and X4, X5, X6. When the S1 button is released, the DVD-player is turned on, while the digital prefix is ​​pressed.

Switch schematic diagram

The switch according to the diagram in Fig. 1 is convenient if you do not need to switch very often, everything is better than poking the plug, but it is simple. It's another matter if you need to switch frequently.

Fig. 1. Schematic diagram switch for audio-video inputs.

There can be two options here - to organize remote control of the input switch using the TV remote control, but this will require a decoder on the microcontroller and select the remote control buttons to control the switch that are not used to control the TV, which is also not always possible.

Controlling the presence of a video signal at the input

The second option, simpler and more practical, consists in controlling the switch based on the presence of a video signal on one of the switchable signal sources. For example, if there is no video signal at the output of the DVD-player (and with the switch power off), a digital set-top box is connected to the TV.

And if there is a video signal at the output of the DVD player (DVD player is on) and the switch is powered, a DVD player is connected to the TV. A switch operating in this way can be made according to the diagram in Fig. 2.

Unlike the circuit in Figure 1, its inputs are switched using an electromagnetic relay of the TRY-12VDC-P-4C type. It is very similar to the RES-22 relay, only the case is plastic, however, RES-22 with a 12V winding will also do just as well.

The relay is controlled by the video signal presence sensor, on transistors VT1-VTZ. It monitors the video input for the DVD player, and as soon as the video signal appears there, switches the TV inputs from the digital set-top box to the DVD player.

Rice. 2. A circuit of the AV input switch with automatic detection of the presence of a video signal.

If there is no video signal at the DVD-player output (connector X3) or the power is off, the contacts of the K1 relay are in the position shown in the diagram. In this case, the signal from the output of the digital set-top box comes to the input of the TV.

When the switch is powered on and the DVD player is on, the video signal is input to the X3 connector. It goes through the R1-C1 circuit to the amplifier stage on the VT1 transistor, which amplifies it in amplitude. Then amplified signal enters the detector on two diodes VD1, VD2 and capacitor C3.

The voltage at C3 increases, which leads to the opening of the VT2 transistor, and after it VT3 opens, through which current flows to the winding of the relay K1. The relay switches its contacts to the opposite position shown in the diagram, and the TV inputs are switched to the DVD player outputs.

While the DVD player is on, its outputs will be connected to the TV. When you turn off the DVD-player, the video signal at its output disappears, and the switch switches back to the digital set-top box. Instead of the TRY-12VDC-P-4C relay, you can use RES-22 with a 12V winding or any other relay with a 12V winding and at least three switching contact groups.

Snegirev I. RK-02-2016.

Electronic circuit breaker Is a simple and inexpensive electronic circuit with a cheap tact button that can control the power on and off of the load. The circuit replaces the more expensive and large mechanical latching switch. The button starts the waiting multivibrator. The output of the multivibrator switches the counting trigger, the logic level of the output of which, changing after each pressing of the button, switches the power supply to the load.

Several different variants of this scheme are possible. A variant in which two are used J-K trigger IC1 and IC2 of a single CD4027B are shown in Figure 1. Feedback coming from the RC-chain connected to the IC1 output to the reset input turns this trigger into a waiting multivibrator. The J input of IC1 is connected to the power bus, and the K input to ground, so the leading edge of the clock pulse at its output is set to "log. one". Tact button turns on between the clock input of the IC1 microcircuit, and the ground. Likewise, the button can be switched between the clock input and the positive VDD power rail. Plugging the J and K pins high turns IC2 into a counting flip-flop. IC2 is switched by the leading edge of IC1's output signal.

You can understand the operation of the circuit by looking at the timing diagrams at its different points, shown in Figure 2. When you press the button, bounce pulses begin to arrive at the IC1 clock input, the leading edge of the first of which sets the output to a high level. Capacitor C1 begins to charge through the resistor R1 to the level "log. one". At the same moment, the rising edge of the pulse arriving at the clock input of the counting flip-flop IC2 switches the state of its output. When the voltage across C1 reaches the RESET threshold of IC1, the flip-flop is reset and the output goes low.

After that, C1 is discharged through R1 to the level "log. O". C1 charge and discharge rates are the same. The duration of the output pulse of the multivibrator must exceed the time of pressing the button and the duration of the bounce. By adjusting the trimmer R1, this duration can be changed in accordance with the type of button used. The complementary outputs of IC2 can be used to drive transistor power switches, relays, or switch-on pins. The circuit operates from 3 V to 15 V and can control power to analog and digital devices.

Is an electronic device assembled on powerful field-effect transistors MOSFETs, which are one of the most important switching elements in modern household and professional electronic technology... Such switches are used mainly in those devices where there are large loads on direct current and are able to replace a highly accurate switching device with the ability to extinguish an electric arc, since such devices often burn out the contact pads due to high currents and become unusable. An electronic switch using MOSFET transistors is not susceptible to such phenomena and does an excellent job of switching loads at high currents and voltages in various power circuits.

Presented here scheme has the ability to easily control the switching of large DC loads using low values impulse voltage- only 5 V. Installed in the circuit MOSFET- NTP6411 transistors are designed to work with a voltage of 100V and a current of 75A, the power of these electronic components is about 200W. Such parameters of the power transistors make it possible to effectively use this electronic switch in the nodes of the car instead of the standard relay. To activate the transistors of the device, both a conventional switch and a pulse input are used, the choice of the input method is carried out by installing a jumper from a piece of insulated wire to the corresponding pins of the connector.

In practice, the impulse voltage input is most efficient and useful since it has low control voltages. The circuit was designed to work with a constant voltage of 24V, but it can be quite successfully used at other voltages, when tested at 12 volts it showed itself to work from the best side, in addition, the installed MOSFET-NTP6411 can be replaced with other N-channel field transistors appropriate electrical characteristics. The diode D1 installed in the circuit performs protective functions, thereby preventing voltage surges emanating from inductive loads. On-board LEDs enable visual monitoring of the status field-effect transistors, and screw terminals provide connection electronic switch in different modules... Upon completion of the assembly of the MOSFET switch, it passed a 24-hour test by operating a solenoid valve with a supply voltage of 24 volts and a current of half an ampere, while the field-effect transistors were completely cold, even in the absence of heat sinks. general scheme has established itself as a reliable device capable of working in a wide variety of fields of application, in including automotive electronics instead of relays or work as a control device in LED lighting.