The phototransistor is a smoke detector. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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The phototransistor is a smoke detector. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Indicators, detectors, metal detectors

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In a fire-fighting device, the principle of operation of which is shown in Fig. 1, a field effect phototransistor having a high sensitivity to changes in illumination is used. The luminous flux from the lighting lamp L1 passes parallel to the window of the phototransistor, and in the absence of smoke, no current flows through the phototransistor.

Phototransistor - smoke indicator
Fig. 1

The appearance of even faint smoke causes light to scatter, some of which enters the phototransistor window. The collector current increases under the influence of the luminous flux, the executive relay R is activated, which turns on the power supply circuit of the device that gives the alarm signal with its contacts.

For similar purposes, an ordinary phototransistor can be used, which is an integral part of a trigger assembled according to the circuit in Fig. 2.

Phototransistor - smoke indicator
Fig. 2

Light control in this device is as follows. In the standby state, transistor T1 is lit, current flows through it, no current flows through transistor T2 and the relay winding P1. Dimming the light output reduces the current through the phototransistor. Transistor Tg goes into saturation mode, its collector current triggers the relay and closes the contacts in the power supply circuit of the signaling device.

Literature

"Toufe I Electronigue", 1969, No. 332

Publication: cxem.net

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Atomic television 30.08.2022

NIST scientists demonstrate the use of Rydberg-state rubidium atoms as receivers that can receive live video and even play video games. A stable radio signal is applied to a glass container filled with atoms in the Rydberg state. The modulated output is then fed to a TV, where an analog-to-digital converter converts the signal into a video graphics array format for display. This work is part of the NIST on a Chip program.

Researchers at the National Institute of Standards and Technology (NIST) have adapted their atomic radio to detect and display color television and video games.

Atom-based communication systems are of practical interest because they can be physically smaller and more tolerant of noisy environments than conventional electronics. The addition of video can improve radio systems, for example in remote locations or in emergencies.

The NIST receiver uses atoms prepared in high-energy Rydberg states, which are extremely sensitive to electromagnetic fields, including radio signals. These sensors also measure the signal strength associated with the International System of Units (SI).

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