Control scheme with DTMF decoder. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Control scheme with DTMF decoder. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The proposed device was conceived as a control system for any processes or devices through a radio transmitter. DTMF signals are used as the encoding-decoding system.

scheme device is shown in Fig.1. The device itself consists of a DTMF decoder based on an MT8870 chip and a decoder based on a 155ID3 chip. For visual indication of the received code, there is a decoder on the K514ID1 chip and a seven-segment ALS321A indicator. This part of the circuit may not be used to simplify the design. The device is powered from a +5 V source. In this design, an integral stabilizer 7805 or a domestic equivalent (EN5A) is used.

The decoder allows you to connect up to 16 actuators. You just need to remember that the actuator must be controlled by TTL levels (0 and +5 V).

Fig.1 (click to enlarge)

Executive device. Here, as an example, is a diagram that I used to determine the coverage of a portable radio transmitter and test various types of antennas. The circuit is made on a 556 chip (dual timer). You can use two timers of type 555 or their domestic counterpart - KR1000VI1. A tone generator is made on one of the halves of the timer, and a waiting multivibrator is made on the second half. The input of the device is connected to the loudspeaker of the radio station. The output of the tone generator is connected to the transmitter's microphone jack. When a command is received from the decoder to the waiting multivibrator, relay K1 (RES-94) is activated and its contacts K1.1 generates a PTT signal for two to three seconds to turn on the transmitter. Thus, when I send a command from a portable transmitter (in this case, the number "4"), I receive in response a tonal message from a stationary transmitter. This device is very convenient when determining the coverage area of a CB radio station installed on a car, you do not need to involve another person who would sit at the base station. Naturally, your mobile station must have a "beeper".

The board for the device was not developed. I did it on a breadboard (Fig. 2), leaving room on it for mounting various additional devices.

Control scheme with DTMF decoder
Ris.2

Of course, in addition to the service proposed above, this device can be used to remotely turn on / off various devices. Also, this scheme is suitable for radio control systems models. To do this, the transmitter must use a DTMF encoder chip used in telephony in dialers. The device can also be used in a telephone set. By supplementing your phone with an auto-hook circuit, you can use this device to control home appliances through your phone.

Author: Nikolay Bolshakov, RA3TOX, Nizhny Novgorod; Publication: N. Bolshakov, rf.atnn.ru

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