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TIME RELAY FOR ELECTROMECHANICAL TOYS

Inexpensive uncontrolled self-propelled electrified toys, mainly made in China, appeared on sale. Their running gear and body are designed in such a way that they can, without the help of a "commander", turn around and tumble, overcome some obstacles encountered on their way. Outwardly, the maneuvers of the toy are somewhat reminiscent of "Roly-Vstanka" - after a somersault, they try to get on the wheels and continue on their way. Unfortunately, it doesn't cost anything for a nimble toy to drop in and "get lost" under a sofa or in another hard-to-reach place. And if there are no adults nearby, the child will not be able or simply will not want to fish out a tractor, tank, jeep from "captivity". As a result, after a few tens of minutes, the battery of the toy will be completely discharged.

It is for such four-wheeled self-propelled guns that the proposed relay is intended, which is distinguished by simplicity, reliability and cheapness of the parts used.

The schematic diagram of the device is shown in fig. one.

The M1 electric motor, the SA2 power switch, the GB1 battery of galvanic cells are self-propelled parts, you install everything else yourself.

When the SB1 button is short-circuited, a high-level voltage is supplied to the control input of the DD1 key through a discharged capacitor C1. The key DD1, which is an enriched field-effect transistor with an n-channel and an insulated gate, opens, the reed relay K1 is activated, its contacts K1.1 are closed. The electric motor is running.

Capacitor C1 is gradually charged through resistor R1, therefore, the voltage at its negative terminal decreases. When it becomes less than 1 ... 1.3 V, the DD1 current switch will close, the K1.1 contacts will open, the engine and all electronics will be de-energized. The charged capacitor C1, when the power is off, will quickly discharge through the diode VD1, the resistor R1 and the motor winding. Capacitor C2 dampens the self-induction pulses of the motor windings and prevents the time relay from starting spontaneously.

The device can use capacitor C1 series K50-35, K53-14, K53-30, C2 - K50-35 or others with low leakage current. In addition to that indicated in the diagram, the diode is any small-sized silicon, for example, the KD102, KD103, KD521 series. Considering the low supply voltage, the current switch must be selected with the lowest possible gate-source threshold voltage, preferably not more than 1,3 V. Of the KR1014KT1A keys tested by the author, approximately every second instance met this requirement

The reed relay is homemade, which uses a low-power reed switch with normally open contacts K1.1 with a case diameter of about 3 mm and a length of 20 mm. The reed switch is tightly wrapped with two layers of thick paper for copier office equipment, two hetin-nax washers with an outer diameter of 8 mm are put on the resulting paper sleeve, which are glued to the sleeve with Moment glue. The resulting frame is removed from the reed switch and installed on a winding machine. The frame is wound in bulk, but evenly, 1800 turns of PEL wire 0,09. You can also use a wire with a diameter of 0,1 ... 0,12 mm, increasing the number of turns by 15 ... 20%. Then the frame with the winding is installed on the reed switch.

The design of the time relay depends on the free volume inside the toy. If it is limited, you can do this: solder capacitor C2 to the motor terminals, and glue the relay and key to the base of the toy. Capacitor C1, diode and resistor are soldered to the terminals of the microcircuit.

As a start button, any suitable PKN series, MP9, VK6 microswitch or similar imported one is suitable. The pusher can be made from a faulty LED or a transistor with a "side". It is convenient to glue the start button to the body of the self-propelled gun with a large amount of hot glue

Although the operating current of the electric motor exceeds the allowable current through the reed switch contacts, you do not have to worry about the reed switch. Firstly, the start of the electric motor is carried out by the button SB1. Secondly, for obvious reasons, the service life of a toy in the hands of a preschooler turns out to be no more than a few weeks, so the contact resource is more than enough.

The exposure time of the relay depends on the ratings of parts C1, R1 and, with a fresh battery indicated on the diagram, is about a minute. And this is more than enough for the toy to meet an insurmountable obstacle on its way.

SENSOR TIME RELAY

Using such a relay, you can turn on a low-power load, say, a small-sized radio receiver, for a certain time. At the end of this time, the load will be de-energized.

The time relay works (see Fig. 2) as follows. When touching the sensor plates E1 and E2 with a finger, the capacitor C1 is quickly charged to a voltage close to the voltage of the battery. At the gate of the transistor VT2, it is limited to 6 ... 7 V using the transistor VT1, which is included as a micropower zener diode. The transistor VT2 opens, the load, in parallel with which the HL1 LED with resistor R1 is connected, is supplied with a supply voltage. The LED lights up.

At this time, the voltage between the drain and source of the transistor VT2 does not exceed 80 mV, so the transistor VT3 is closed.

Further, the capacitor is gradually discharged through the resistor R1 and the leakage resistance of the transistors. As the capacitor discharges, the voltage at the gate of the transistor VT2 decreases, and between the drain and its source it increases. As soon as it rises to about 1,5 V, the VT3 transistor will start to open. The rate of discharge of the capacitor through this transistor and resistor R3 increases like an avalanche, and the transistor VT2 closes abruptly. The load voltage drops. The duration of the relay exposure depends mainly on the capacitance of the capacitor.

If it is necessary to de-energize the load before the end of the exposure, touch the sensor plates E4, E2 with your finger. As a result, the capacitor will quickly discharge and the transistor VT1 will be closed. The sensitivity of the time relay when touching the plates E2, E3 depends on the resistance of the resistor RXNUMX.

The device can use MLT, MT, S2-23 resistors, a capacitor of the K10-17, K73-15, K73-17 series, K501 field-effect transistors with letter indices A-B or keys KR1014KT1, KR1064KT1 replacing them, bipolar - any of the series KT315 LED - series KIPD21 with letter indices K-P or another with increased brightness.

With the capacitor capacitance indicated in the diagram, the time delay is approximately 2 minutes, with a 0,01 microfarad capacitor - 10 minutes, and a 0,022 microfarad capacitor - 40 minutes. Depending on the transistors used, the shutter speed may differ from these values, so set the desired duration by selecting a capacitor. By selecting the resistor R3, achieve such a sensitivity of the device at which it is triggered by lightly touching the sensor plates E1, E2 with your finger. If, when checking the device, the voltage between the drain and the source of the open transistor VT2 exceeds 50 mV, connect 1-3 of the same transistors in parallel with it.

The time relay can be built into any design or assembled in a separate case as an attachment. In any variant, the load power circuits are connected to terminals X1, X2, and parts HL1, R2 can be disconnected. The relay is powered from a design source with a voltage of 4 ... 10 V. But, in principle, it is permissible to apply a voltage of more than 10, but less than 40 V to it. In this embodiment, a resistor with a resistance of 2 ... 3 must be connected between the drain of the transistor VT1 and the gate VT10 MΩ, and solder a low-power bipolar transistor to the gate and source terminals of VT3, as was done for VT2. Moreover, it is desirable to select the transistor VT3 with the lowest possible gate-source threshold voltage.

You may wish to build a relay into the multimeter. Then you need to replace the touch plates with small-sized buttons, install an oxide capacitor with a low leakage current and a capacitance of 1 ... 100 μF, connect a resistor with a resistance of 10 ... .100 kOhm

Author: A.Butov, village of Kurba, Yaroslavl region

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