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Light-controlled energy-saving relays

Status: Proposal
April 23, 2019
Light-controlled energy-saving relays
Michael A. Shustov (Russia), Andrey M. Shustov (Germany)
Two circuits of energy-saving relays controlled by light or buttons are introduced. Those two are intended for short-term switch-on of light.
In previous publications [1, 2], we described devices, that enable the switching-on or the switching-off (manually or automatically) of electric light sources by pushing on any of the normally closed push-buttons connected in series. Below, based on one of the circuit-design of energy-saving relays given in [2], the possibility of combined button-and-light control of their operation is presented.
The energy-saving relay (Figure 1) differs from its predecessor [2] by the presence of two new elements: the resistor R2 and the phototransistor T3. The implementation of these elements made it possible to give the device new, unusual properties. In addition to the common feature to switch-on the light for a given time duration by pushing any of the buttons connected in series, the device can be activated by short light exposing of the phototransistor T3, for example, by a flashlight, car headlight, a laser pointer beam, etc. As a result, the light source (lamp LA1) or other load (relay, electric lock, garage gate control mechanism, alarm siren, indicator light of target shooting, etc.) is switched-on for a predefined time duration.
In the initial state, the capacitor C1 which defines the time constant, is charged via the load resistance (LA1) and the diode D1 up to the level of supply voltage. The light-emitting-diode LED1 indicates the ready-state of the device for operation as well as indicates its location. By pushing any of the buttons SB1-SBn (common useability), or by short light exposing of the phototransistor T3, the electronic switch on the transistors T1 and T2 is activated and self-locked. As the result, the load (LA1) is connected to the power supply for a period of time determined by the discharge time of the capacitor C1 to the potentiometer R4. After the discharge of the capacitor, the load is switched-off, the device returns to its original state. The time duration for switching-on the load can be smoothly controlled by adjusting the trimming potentiometer R4 in the range from 0 to 50 seconds. This time duration can be changed by using of the capacitor C1 and the potentiometer R4 with other nominal values.
The transistor T2 2N7075 (2N7085) with a heat sink is able to provide a load current up to 30 (20) A. The device is also able to work with other supply voltages by means of the appropriate correction of the electronic components.

Figure 1. Energy-saving relay with light beam control or normally closed push-buttons.
The second energy-saving relay (Figure 2) works in a different way: it operates, if you shortly pushed one of the SB1-SBn buttons as well as in case if the light exposing of the phototransistor T1 has being interrupted. The operating principle of the relay remains unchanged. Such an energy-saving relay can be installed, for example, at a building entrance or at a gate. The phototransistor T1 can be exposed by the light of directional beam of a laser pointer or by a light-emitting-diode located on the opposite side of the hallway or other room. When somebody crosses this light beam, the relay is activated, the light is switched-on for a predetermined time duration (from 0 to 50 seconds, potentiometer R3).

Figure 2. Energy-saving relay with commutation by a reflected light beam or by normally closed push-buttons.
An installing of an auxiliary light source on the opposite wall of the room is irrational, because it requires an additional power source. It is more reasonable to install the auxiliary light source directly into the energy-saving relay (Figure 3). The light of directional beam of a laser pointer or of the light-emitting-diode (LED1), for example from an old remote control operating in the visible or infrared range, reaches the mirror installed on the opposite wall of the room, and reflects back to the phototransistor T1. When the light beam is interrupted by a passing-through person, the energy-saving relay switches-on the light for a predetermined time duration.

Figure 3. Interruption of a light beam reflected by the mirror by a person passing the hallway
  1. Shustov M.A. Multi-switch Lights Control. For corridors and hallways // Elektor. – 2014. – V. 40 (450). – № 6. – P. 74–75.
  2. Shustov M.A., Shustov A.M. Energy-saving relays // Elektor. – 201x (in print).
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