an old friend is better than two new ones

Published on May 24, 2016

an old friend is better than two new ones

    After moving to a new apartment, first of all I decided to set the bell. But this task was not easy. The fact is that the developer installed the bell button only at the entrance door, and there was no button at the entrance door of the vestibule. Since the old bell was electromechanical and was activated according to the scheme via a button, additional cable was required for it. But the attempt to lay the wire in the vestibule was a failure. The walls of the vestibule were made of durable concrete, and the usual drill with perforator function simply bounced off the wall. In order not to spend money on acquiring an expensive professional tool, it was decided to buy a simple Chinese wireless call. Plus the absence of extra wires in sight. But it also turned out to be difficult. Inexpensive calls had poor sound quality and a banal set of tunes, who get tired after the first month of operation. In the end, it was possible to find a suitable call with a less pleasant sound. Oddly enough, it was an electromechanical, only with an integrated wireless module. Everything is fine, but it disappointed the price of this call, it cost 9000 rubles.

    As a result, they decided to temporarily leave their good old electromechanical call. That would be the end of it, but the lack of an external button at the vestibule door periodically made itself felt. It was decided to make a wireless call.

    To implement the project, several devices operating in the 433 MHz band were selected from the Master Kit range of wireless modules: MP324M , MP324M / transmitter , MP220V and MP246 .

    I think the question will immediately arise, what is the MP220V sensor for? Actually, everything is simple, the developer of this sensor put an additional opportunity in it, namely: with the help of simple manipulation of the soldering iron, the sensor turns into a compact embedded power source with a current of up to 80 mA and a voltage of 5V or 12V to choose from. By default, the module is set to a voltage of 5V. Since there is little space in the case of the bell, it was chosen to power the MP324M receiver.

    But every good thing has its drawback, in this case, the lack of electrical isolation from the network. Therefore, when setting up, you must follow the electrical safety rules. And the installation of the scheme to produce only in a de-energized state. To put this module into power supply mode, you need to use a soldering iron to jump the jumpers –V, RL and + V, RL to the position 1-2. In principle, nothing prevents you from using a board from a 5V cell phone adapter if space permits.

    For compactness, the variable resistor of the MP246 power module can be removed. By installing a jumper instead of the usual installation wire or from the output of the DIP resistor, which was actually done.

    To build the circuit, you will need one DIP resistor with a nominal value of 10-15 kΩ and an electrolytic capacitor with a nominal value of 47 μF with a voltage not lower than 6V. In principle, the capacitor can be excluded from the circuit. But the pulse duration at the output of the MP324M receiver seemed to me long, so this chain was installed. By reducing and increasing the capacitance of the capacitor, you can adjust the pulse duration. Since different calls have different designs, this may be necessary when adjusting the sound. A resistor installed in parallel to the circuit, discharges the electrolytic capacitor, so that the bell can be triggered again.

    Connection diagram:

    After assembling the call control scheme, connect the construction to the network and register the receiver. To register, briefly press the button on the receiver, then press the buttons on the transmitter, after a few seconds pairing will occur. Now when you press the first button on the transmitter should ring. Thus, we add and check the second console.

    The photo of the layout of the modules in the bell:

    After checking, the bell case closes and is set in place:

    You ask how we can power the assembled device. After all, the line connecting the call voltage appears only when you press the button when you call. In fact, everything is simple, we will provide the power of the call when you modify the button.

    To begin with, it is desirable to de-energize the part of the circuit where we will make the modification. We take out the button from the box and connect two standard wires with each other, isolating them with tape. This connection will give us a constant power 220V. The current consumption, in standby mode, is tens of microamps. Therefore, the constant inclusion does not affect the payment of electricity.

    Now we disassemble, transmitters and solder two wires parallel to the first buttons. The resulting conclusions are cleaned and connected to the contacts of the removed button. For greater reliability, transmitters can be wrapped with one layer of electrical tape.

    Wiring diagram of the transmitters to the call buttons:

    Now set the button in place and check the operation of the call.

    In the same way, we assemble the second button and fix its case on the tambour door, for example, on double-sided tape. Although I still managed to drill the wall to a small depth and fix it on two small screws.

    Well, that's all you can use.

    If after a couple of years one of the buttons stops working, do not panic, it's just time to replace the batteries. Transmitters are powered by 12V from element 27A, which can be freely purchased at any supermarket. I think this will definitely not be a problem. In this scheme, the elements work for a year. And since we do not use the call often, I think that in this mode they will work for at least another couple of years.

    The device can be viewed on the video:

    Solution author: Vladimir Rublev (UA4LOU)