Touch time relay for electromechanical toys. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur
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The device is intended for installation in a children's electromechanical toy and allows you to extend the service life of chemical current sources. It will automatically turn off the power to the structure after a specified time. For children's toys, the presence of such a function is relevant, since a child can lose interest in it at any time without turning off its power with the built-in switch.
Fig. 1
The time relay circuit is shown in fig. 1. After the supply voltage is applied, the capacitor C2 is discharged, all transistors are closed and the electric motor (or motors) is not powered, and there is no current consumed. The relay is started by simultaneously touching the sensor elements E1, E2 with your fingers or palm, while the opening voltage will be applied to the gate of the field-effect transistor VT2. Following it, transistors VT3 and VT4 will open, and the electric motor will start to work. If you release the sensor elements, the transistor VT2 will close, but the charging of the capacitor C2 will begin through the resistors R2, R3, R6, the emitter junction of the transistor VT3 and the open channel of the transistor VT4. Due to this current, VT3 and VT4 remain open and the supply voltage is supplied to the electric motor. In this case, the voltage drop across the transistor VT4 will not exceed 50 mV, and the maximum current through it should not exceed 3 A.
When the charging of the capacitor C2 is over, the transistors VT3 and VT4 will close and the motor will be de-energized. For the elements indicated in the diagram, with a supply voltage of 3 V and a load current of 0,5 A, the power-off delay will be about 120 s. Touching the sensor elements again will open the transistors VT2-VT4, and the capacitor C2 will quickly discharge through the open transistors VT2, VT4 and the current-limiting resistor R6. Therefore, after releasing the sensor elements, the shutter speed countdown will begin again.
The emitter junction of the transistor VT1 works as a micropower zener diode and protects the gate of the field effect transistor VT2. Capacitor C1 suppresses high-frequency interference, resistor R1 is current-limiting.
Fig. 2
Electric motor M1, power switch SA1 and battery GB1 are regular elements of the toy. The rest of the parts, except for the sensor elements, are placed on a single-sided printed circuit board, the drawing of which is shown in fig. 2. If no holes are drilled in the board, the elements can be soldered directly to the corresponding contact pads, which will reduce the overall dimensions of the mounted board. Resistors C2-23, P1 -4 are used, capacitor C1 is K10-17, K10-50, the rest are small-sized low-profile imported oxide, C2 should have as little leakage current as possible, so it is desirable that it be tantalum.
Instead of the KP505G field effect transistor, any of the KP505, BSS88, BSS295 series, as well as an instance from the KP501, KP504, ZVN2120 series with a threshold voltage of not more than 2 V at a drain current of 100 μA, will do. Transistors 2SA993 can be replaced by any KT3107, 2SA104, 2SA109, 2SA1048 series. Replacing the field effect transistor FDD6530A - AP9916H, P45N02LDG. During installation, the gate and source terminals of the field-effect transistors are connected with a wire jumper to prevent damage to them.
As sensor elements E1, E2, you can use metal trim elements of the toy, for example, decorative door handles of a car model, while the body itself must be plastic. The elements are placed so that they are closed by the fingers or palm when the toy is picked up.
Setting up the device consists in setting the exposure time by selecting capacitor C2. For uncontrolled electromechanical toys, it is preferable to set it in the range of 15 ... 30 s, and for radio-controlled toys - 2 ... 10 minutes. It should be noted that when the supply voltage of the device decreases, the exposure time also decreases. Instead of an electric motor, there may be another load, for example, incandescent lamps or various electronic components.
Author: A. Butov
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