A device from a coronavirus or another trolley from a loaf of bread?

This is another story and a guide to creating a device to protect against coronavirus. Surely everyone noticed that the radiant quartz lamps from the Soviet past were undeservedly forgotten, but in the current situation they can become an assistant in solving the common problem with coronavirus.

Quartz lamp - an electric mercury discharge lamp with a quartz glass bulb designed to receive ultraviolet radiation (in particular the UVC range).

Quartz lamps often have the following spectra:


Source: Low-pressure & medium-pressure mercury lamps compared to E. coli germicidal effectiveness curve. Ultraviolet Germicidal Irradiation Handbook, Fig. 2.1.

The main bactericidal component of the spectrum (as follows from the figure) are wavelengths of about 260 nm. The emission spectrum of the lamp is due to the composition of the gas mixture inside the bulb. It is also worth highlighting spectral lines below 185 nm (they are not shown in the previous figure), which in the environment intensively generate ozone from oxygen.

Quartz lamps have the following advantages:
no consumables are needed to disinfect the room;
do not require mechanical impact on the environment in order to carry out disinfection;
Minimal operator effort

But there are significant disadvantages:
direct and reflected UVC rays are harmful to humans;
generated ozone is also harmful to humans by inhalation;
there are no available means to control ozone concentration at the desired point in the room;

The first two points of the disadvantage can be eliminated only by the complete absence of a person in the treated room. You can find solutions with timers and remotes at 433 mhz, but in fact they are primitive and difficult to integrate into the smart home system.

Given this, it was decided to purchase a quartz lamp and a controller to solve the problem of integrating the lamp into the smart home system. An 8 W quartz lamp and a Sonoff controller (based on esp8266) were ordered.

Soon this lamp was received and, oddly enough (despite excellent reviews), it turned out to be inoperative. Opening it, the following was observed:



This resistor burst during the filament of a quartz lamp, by the way pay attention to the silkscreen of the board ...

It was decided to replace this faulty circuit with a circuit from the legendary 15w gas-discharge "energy-saving" lamp.



Removing the circuit from the lamp found is still a quest. Since it was required to carefully open the body of this lamp without damaging the bulb (it contains mercury vapor). As a result, the circuit was successfully retrieved. The following figure shows a similar circuit with a “pinout”:


Photo taken from here

Quartz lamps are similar in design and operation to other gas discharge lamps (except that a quartz bulb without a phosphor is used). They have two filaments, each of which has two leads as well as in "energy-saving" lamps. As it turned out in practice, in both types of lamps, the filament has the same resistance of 8 ohms. But in any case, it is necessary to measure the resistance of the filament of both types of lamps to make sure that the resistances are the same.

The circuit from the "energy-saving" lamp was installed in an elegant case:



As a result of an unexpected alteration of the quartz lamp, now it has a power of not 8 watts, but 15 watts. The following should be noted here, quartz lamps use about 20% of the consumed energy to generate ultraviolet radiation, and therefore in my case the effective power is 3-4 watts.

After receiving the Sonoff basic module, it was decided to upgrade it to Tasmota custom firmware. Custom firmware makes it possible to control not only the electromagnetic relay, but also makes it possible to connect sensors via the i2c, SPI bus in order to expand the functionality. Not to mention the fact that it can be easily integrated into a smart home system.

→ Firmware Tasmota
→ EEPROM procedure for Tasmota

Of course, for flashing it was required to output UART:



The developed device connection scheme is presented below:



Using the following solution, you can quartz the desired room by controlling the process remotely - on the street, at work or in another room, without fear of exposure or breathing in during manual on / off lamps.

By the way, in this way, you can add an ozone concentration sensor MQ-131 (it datasheet ) to the local network of devices . The sensor itself can be installed in any other microcontroller that supports Wi-fi and ADC. This solution will allow you to install this sensor in any place of the room where it is critical to know the concentration of ozone in the air, with automatic control of a quartz lamp.

The device itself is presented below:



Remember that such bulbs of discharge lamps contain mercury, so be careful with them! And take all precautions during quartzing!

PS 1 - I made a device for the evening, so there may be flaws in the description and its implementation.
aqicn.org/air/view/sensor/spec/o3.winsen-mq131.pdf - I am not responsible for any possible harm caused by the materials in this article (although the purpose of this article is to benefit the public).