Baby monitor - good "bug"
It so happened that the appearance of a child in the family coincided with financial difficulties. But the lack of time and money can not stifle the care of the baby and the thirst for knowledge of the new.
The article does not claim to be new, and all the technologies used in it are pretty well spread over the Internet. But I hope all of the following will help you decide to help your loved ones and make your child's sleep calm. Consider, I never studied the “radio craft” anywhere, but I was able to assemble a device that has been working properly for two years now. All that is needed is a soldering iron, multimeter and patience.
Prehistory In the summer period, the wife and child spend quite a lot of time at the dacha of the Soviet type: the area around the edges of which are scattered are a number of buildings. The conditions for the overnight stay are in the house, but almost all the bright time vacationers spend near the summer kitchen located at the opposite end of the site at a distance of about 50 meters. A tolerable asphalt road leads to the dacha settlement, so throughout the day it drives vehicles of “businessmen” accepting scrap metal, selling products of the village and technologies that allow summer residents to realize their cherished dream - to achieve a harvest similar to what these businessmen deliver. But the mentality of our people is such that all these machines use their horn with an interval of several minutes to increase the profitability of the business.
The sum of these factors inspired me to think about the need for a baby monitor: for a child to sleep, it is necessary to close all windows and doors, but in the daytime his wife is spinning around the summer kitchen and is simply unable to hear when the baby wakes up. Yes, and awakenings are sometimes short-term, it is worth pumping up in time and healthy sleep will last for another hour. So I had to sit quietly in the house for several day hours, or find the child in hysterics and not sleep.
A little googling I was upset the minimum price of the baby monitor which I then found was $ 50, and reviews about models with a similar price were mostly negative, good ones cost about $ 100. But then I remembered my unfulfilled childhood dream: to solder the “scouts” and this pushed me to action. They have a lot in common: compact size, low consumption (long battery life), short range (more on this below).
The main idea of ​​homemade bugs is the use of available components and ready-made devices to reduce the cost of construction. So the broadcast is conducted on frequencies that household radios are capable of receiving and now the price of the device has already decreased more than twice. But due to the fact that, though with good intentions to broadcast on these frequencies without special licenses, it is impossible, then low output power is used and the choice of the frequency as far as possible from the occupied radio stations. I chose a range of 88-108 megahertz with frequency modulation in common FM.
')
Further there was a reading of a set of specialized forums for a choice of the scheme. The frequency stability has been added to my parameters. As it turned out for such small devices, often with minimal shielding and the most important placement in various places - the frequency drift from the intended one can be quite significant. Placed the device closer to the body of the child or hitched to the iron bed and again a dreary setting. Also, initially I used to power the nanny batteries, the discharge of which also drove the frequency.
In the end, I chose a compromise between the complexity and stability of the device and stopped at the scheme from the link . The essence of the device there is disclosed in some detail, but I will dwell on the changes that I have made to the design and the nuances that are obvious to forum participants, but difficult for mortals like me.
1. Fee. I used TNT montage (one of the oldest and most widely described) on a two-sided board (for better shielding).
When assembling, not all components can be obtained exactly according to the scheme due to the variation of parameters and the lack of standards in some parts (in this scheme, this is just a microphone - taken from broken computer headphones). But it’s not for nothing that I proposed this very scheme, since it will work, albeit not in the optimal mode, without additional configuration.
In my case, the differences are:
- the microphone resistor turned out to be 22k (in the 39k diagram) - but you can use a variable resistor to regulate the sensitivity of the microphone
Optional:
- a 330 ohm resistor is replaced by an inductance of 5-10 ÎĽH (quietly this wind does not need to be sold as a regular part) to improve efficiency
- added another variable capacitor in front of the antenna for minimum matching.
- added LED and (+ selected resistor) as an indicator of performance
- soldered to the board above the coil screen (found in any Soviet radio) to improve shielding
- Added a switch for three positions allowing you to switch between an external power source, batteries and turn off the device. (Can be used in two positions, but then you need to fence gardens with a protective diode so as not to apply voltage from an external power supply when batteries are inserted, and the diode during battery operation will squander the voltage, which will reduce the operating time and radius)
All items can be bought from a specialty store, and on the radio market - there are no rare ones, the total cost is about $ 6.
2. Housing. The device will be used by women. And even give them the perfect circuit board is equivalent to the fact that you just throw it.
According to the examples of many articles, I used a box for 4 batteries, using two compartments for their intended purpose, and the board itself was placed in the two remaining ones.
3. Antenna. The laws of physics are inexorable and the size of the antenna is primarily dictated by frequency. Namely, it should be a multiple of the wavelength, which is why an antenna in the form of a 170 cm long wire is proposed in the link. Frankly speaking, it is inconvenient to use it. You can also take a quarter-wave telescopic (from any modern radio), but it is also quite fragile. And after some time of use, I assembled an antenna similar to that used in modern portable radios based on the ideas and calculations from this article .
4. Customization. For a radio transmitting device, at least a minimum setting is needed. In our case, these are games with a coil and a variable capacitor parallel to it to drain the frequency into the free range (in my case 90 MHz).
Important! Twist the capacitors (and indeed stretch the coil) need not a metal object. Otherwise, when you remove your hand, the frequency will go away again. I cut myself like a screwdriver from sushi sticks.
After changing the type of antenna, my transmission range decreased dramatically (up to 20 m), to match the antenna I added a terminal variable capacitor. But it is not possible to tune it by ear in modern digital receivers. Therefore, if you, like me, do not have a friend of a radio amateur with a radiometer, collect yourself a Polyakov resonant wave meter. I tried several wave metering schemes, but only this one worked normally.
The only thing that can cause difficulties for you is the search for a germanium diode. Modern industry has almost abandoned them, but they are still in abundance on the radio market.
We connect the leads of the wavemeter to the multimeter and begin to rotate the output stage capacitor until the maximum multimeter is reached (using the same wooden screwdriver). A multimeter is preferably an arrow, but it turned out on me and on the digital one just needs to be adjusted more smoothly and in the end longer.
5. Power supply. Initially, everything worked on batteries, since the current in the power circuit was about 5.24 mA, which is estimated to be about 1000 hours. But the reality is that manufacturers lie with the actual capacity of the batteries and in the operation mode, the voltage gradually decreases - as a result, the device will stop working long before the elements are completely discharged. A converter circuit here is not suitable because of the "noise" of the latter. The voltage drop also leads the frequency, and in the country the radio turned out to be without auto-tuning (now a rarity). As a result, I decided to power the circuit with the help of a power supply unit (any suitable for 3-5 V) from some kind of dead device.
But here is another difficulty, the search for the solution of which took more than a week (well, I have no friend of a radio amateur). The radio nurse began to nastily fade, while switching to the batteries fixed everything. I tried three options of filters on nutrition, but to no avail. I wanted to quit the venture, but I stumbled upon the mention that each diode of the PSU bridge was enough to be bridged by a 10n capacitor. And lo and behold, the noises disappeared by 99%.
The result: an excellent clear sound at a distance of about 150 meters, the sensitivity of the microphone is such that it even had to be reduced, takes on any household radios - the baby sleeps well.
A couple more tips:
Remember that the waves travel in all directions and you have another source of information leakage. On the old Soviet walkie-talkie there was always a sign in a prominent place “Caution! The enemy overhears ":)
In order to avoid misunderstandings, it is better to sign the device. Legally, using it you are still not right all right, however, as well as thousands of users of automotive FM transmitters. But in the forums, a part of the population living in Russia mentioned unpleasant incidents with law enforcement agencies. And the nerves of loved ones must be protected.
Well, now what happened with me.
For the quality of the soldering on the part of the installation, do not judge strictly, I have a 30W soldering iron, it is simply not able to heat anything more than the legs of the radio component. I can not lay out the soldering side for this, it is necessary to disassemble the antenna, and during the assembly process (a year ago) I did not guess to make a photo session. Yes, and on the above site there are several layout options in many modern formats.
Pay
General form
Microphone Holes
External power socket
Several original ideas, and especially regarding the “Chinese” alarm clock, were drawn from this article.
PS The topic was written under the “DIY or Do it yourself” hub, so if innovative technologies do not apply strictly in the article.
The article does not claim to be new, and all the technologies used in it are pretty well spread over the Internet. But I hope all of the following will help you decide to help your loved ones and make your child's sleep calm. Consider, I never studied the “radio craft” anywhere, but I was able to assemble a device that has been working properly for two years now. All that is needed is a soldering iron, multimeter and patience.
Prehistory In the summer period, the wife and child spend quite a lot of time at the dacha of the Soviet type: the area around the edges of which are scattered are a number of buildings. The conditions for the overnight stay are in the house, but almost all the bright time vacationers spend near the summer kitchen located at the opposite end of the site at a distance of about 50 meters. A tolerable asphalt road leads to the dacha settlement, so throughout the day it drives vehicles of “businessmen” accepting scrap metal, selling products of the village and technologies that allow summer residents to realize their cherished dream - to achieve a harvest similar to what these businessmen deliver. But the mentality of our people is such that all these machines use their horn with an interval of several minutes to increase the profitability of the business.
The sum of these factors inspired me to think about the need for a baby monitor: for a child to sleep, it is necessary to close all windows and doors, but in the daytime his wife is spinning around the summer kitchen and is simply unable to hear when the baby wakes up. Yes, and awakenings are sometimes short-term, it is worth pumping up in time and healthy sleep will last for another hour. So I had to sit quietly in the house for several day hours, or find the child in hysterics and not sleep.
A little googling I was upset the minimum price of the baby monitor which I then found was $ 50, and reviews about models with a similar price were mostly negative, good ones cost about $ 100. But then I remembered my unfulfilled childhood dream: to solder the “scouts” and this pushed me to action. They have a lot in common: compact size, low consumption (long battery life), short range (more on this below).
The main idea of ​​homemade bugs is the use of available components and ready-made devices to reduce the cost of construction. So the broadcast is conducted on frequencies that household radios are capable of receiving and now the price of the device has already decreased more than twice. But due to the fact that, though with good intentions to broadcast on these frequencies without special licenses, it is impossible, then low output power is used and the choice of the frequency as far as possible from the occupied radio stations. I chose a range of 88-108 megahertz with frequency modulation in common FM.
')
Further there was a reading of a set of specialized forums for a choice of the scheme. The frequency stability has been added to my parameters. As it turned out for such small devices, often with minimal shielding and the most important placement in various places - the frequency drift from the intended one can be quite significant. Placed the device closer to the body of the child or hitched to the iron bed and again a dreary setting. Also, initially I used to power the nanny batteries, the discharge of which also drove the frequency.
In the end, I chose a compromise between the complexity and stability of the device and stopped at the scheme from the link . The essence of the device there is disclosed in some detail, but I will dwell on the changes that I have made to the design and the nuances that are obvious to forum participants, but difficult for mortals like me.
1. Fee. I used TNT montage (one of the oldest and most widely described) on a two-sided board (for better shielding).
When assembling, not all components can be obtained exactly according to the scheme due to the variation of parameters and the lack of standards in some parts (in this scheme, this is just a microphone - taken from broken computer headphones). But it’s not for nothing that I proposed this very scheme, since it will work, albeit not in the optimal mode, without additional configuration.
In my case, the differences are:
- the microphone resistor turned out to be 22k (in the 39k diagram) - but you can use a variable resistor to regulate the sensitivity of the microphone
Optional:
- a 330 ohm resistor is replaced by an inductance of 5-10 ÎĽH (quietly this wind does not need to be sold as a regular part) to improve efficiency
- added another variable capacitor in front of the antenna for minimum matching.
- added LED and (+ selected resistor) as an indicator of performance
- soldered to the board above the coil screen (found in any Soviet radio) to improve shielding
- Added a switch for three positions allowing you to switch between an external power source, batteries and turn off the device. (Can be used in two positions, but then you need to fence gardens with a protective diode so as not to apply voltage from an external power supply when batteries are inserted, and the diode during battery operation will squander the voltage, which will reduce the operating time and radius)
All items can be bought from a specialty store, and on the radio market - there are no rare ones, the total cost is about $ 6.
2. Housing. The device will be used by women. And even give them the perfect circuit board is equivalent to the fact that you just throw it.
According to the examples of many articles, I used a box for 4 batteries, using two compartments for their intended purpose, and the board itself was placed in the two remaining ones.
3. Antenna. The laws of physics are inexorable and the size of the antenna is primarily dictated by frequency. Namely, it should be a multiple of the wavelength, which is why an antenna in the form of a 170 cm long wire is proposed in the link. Frankly speaking, it is inconvenient to use it. You can also take a quarter-wave telescopic (from any modern radio), but it is also quite fragile. And after some time of use, I assembled an antenna similar to that used in modern portable radios based on the ideas and calculations from this article .
4. Customization. For a radio transmitting device, at least a minimum setting is needed. In our case, these are games with a coil and a variable capacitor parallel to it to drain the frequency into the free range (in my case 90 MHz).
Important! Twist the capacitors (and indeed stretch the coil) need not a metal object. Otherwise, when you remove your hand, the frequency will go away again. I cut myself like a screwdriver from sushi sticks.
After changing the type of antenna, my transmission range decreased dramatically (up to 20 m), to match the antenna I added a terminal variable capacitor. But it is not possible to tune it by ear in modern digital receivers. Therefore, if you, like me, do not have a friend of a radio amateur with a radiometer, collect yourself a Polyakov resonant wave meter. I tried several wave metering schemes, but only this one worked normally.
The only thing that can cause difficulties for you is the search for a germanium diode. Modern industry has almost abandoned them, but they are still in abundance on the radio market.
We connect the leads of the wavemeter to the multimeter and begin to rotate the output stage capacitor until the maximum multimeter is reached (using the same wooden screwdriver). A multimeter is preferably an arrow, but it turned out on me and on the digital one just needs to be adjusted more smoothly and in the end longer.
5. Power supply. Initially, everything worked on batteries, since the current in the power circuit was about 5.24 mA, which is estimated to be about 1000 hours. But the reality is that manufacturers lie with the actual capacity of the batteries and in the operation mode, the voltage gradually decreases - as a result, the device will stop working long before the elements are completely discharged. A converter circuit here is not suitable because of the "noise" of the latter. The voltage drop also leads the frequency, and in the country the radio turned out to be without auto-tuning (now a rarity). As a result, I decided to power the circuit with the help of a power supply unit (any suitable for 3-5 V) from some kind of dead device.
But here is another difficulty, the search for the solution of which took more than a week (well, I have no friend of a radio amateur). The radio nurse began to nastily fade, while switching to the batteries fixed everything. I tried three options of filters on nutrition, but to no avail. I wanted to quit the venture, but I stumbled upon the mention that each diode of the PSU bridge was enough to be bridged by a 10n capacitor. And lo and behold, the noises disappeared by 99%.
The result: an excellent clear sound at a distance of about 150 meters, the sensitivity of the microphone is such that it even had to be reduced, takes on any household radios - the baby sleeps well.
A couple more tips:
Remember that the waves travel in all directions and you have another source of information leakage. On the old Soviet walkie-talkie there was always a sign in a prominent place “Caution! The enemy overhears ":)
In order to avoid misunderstandings, it is better to sign the device. Legally, using it you are still not right all right, however, as well as thousands of users of automotive FM transmitters. But in the forums, a part of the population living in Russia mentioned unpleasant incidents with law enforcement agencies. And the nerves of loved ones must be protected.
Well, now what happened with me.
For the quality of the soldering on the part of the installation, do not judge strictly, I have a 30W soldering iron, it is simply not able to heat anything more than the legs of the radio component. I can not lay out the soldering side for this, it is necessary to disassemble the antenna, and during the assembly process (a year ago) I did not guess to make a photo session. Yes, and on the above site there are several layout options in many modern formats.
Pay
General form
Microphone Holes
External power socket
Several original ideas, and especially regarding the “Chinese” alarm clock, were drawn from this article.
PS The topic was written under the “DIY or Do it yourself” hub, so if innovative technologies do not apply strictly in the article.
Source: https://habr.com/ru/post/180917/
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