Motorcycle intercom. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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A normal conversation between the driver and a passenger of a motorcycle while driving is possible only when using a special intercom - intercom.

An analysis of the noise generated during the movement of a motorcycle showed that the main part of their acoustic impact lies in the region of low frequencies (from engine operation - up to about 500 Hz) and high frequencies from a powerful oncoming air flow - over 3 kHz). Therefore, when developing the intercom device, great attention was paid to the creation of a band pass filter with a bandwidth in the range from 600 Hz to 3 kHz. The device uses a combined band-pass filter with a frequency response decay of 18 dB/oct in the high-frequency part and 6 dB/oct in the low-frequency part.

The schematic diagram of the device is shown in fig. one.

On fig. 2 shows a diagram of one of the two amplification channels. The second channel is identical. The audio signal from the BM1 microphone (Fig. 1) through the capacitor C1 is fed to the inverting input of the DA1.1 microcircuit. The second half of the microcircuit (the numbering of its outputs is indicated in brackets) was used to build a similar cascade of the second intercom channel.

The cutoff frequency of the second filter is determined by the elements R5, R6. C3 and C4, and the voltage divider on resistors R3 and R4 creates the necessary bias on the non-inverting input when powered by a unipolar current source.

The audio frequency power amplifier (UMZCH) in each channel is made on a separate microcircuit (DA2 for the channel indicated on the diagram). The optimal gain (depending on the individual characteristics of the driver and passenger hearing and the traffic conditions when driving) is set by a variable resistor R8 and a tuned R9.

Capacitor C6, together with elements C8 and R2, ensure the stability of the UMZCH. Elements C7. C11, R7 and C12 prevent unwanted power feedback.

The power circuits (Fig. 1) are built so that it is possible to use any type of current source - a battery of four AA galvanic cells or batteries of the same size, as well as an on-board battery or generator. To separate the influence of sources, diodes VD1 and VD2 are introduced. When powered from the on-board network of a motorcycle, to suppress interference, including impulse ones, the voltage is supplied to the intercom through a DA3 microcircuit stabilizer. The HL1 LED is turned on in the stabilizer's common power bus circuit. This stabilizer provides a voltage of 6,5 ... 7 V at the output. Therefore, the on-board source will be dominant even with a fresh GB1 battery.

Pairs of microphone-loudspeaker for the driver and passenger are located in individual motorcycle helmets. For each of the pairs, standard five-pin connectors from sound amplifying equipment are used. Pin 5 of the block part of connector X1 is connected to pin 4 of connector X2. This is a common power rail circuit. Therefore, if one of these connectors is undocked when the motorcycle is stopped, the entire system is de-energized. This is a kind of protection against unproductive energy consumption.

On fig. 1 also shows that the BM1 microphone is connected to the second channel of the amplifier), and the BM2 microphone is connected to the first one, thus creating a cross-talk between the driver and the passenger.

We recommend starting the adjustment of the device when working from the on-board network of the motorcycle. Apply a voltage of 12 ... 15 V to the stabilizer and check the voltage at its output - it should be about 6.5 V (measured between the VD1 anode and the common power bus or the negative terminal of the GB 1 battery connection). The current consumption in the silent mode of both operators should not exceed 5 mA.

The dual operational amplifier LM1458 contains two 0УμА741 in one package (full analogue - 140UD7). Other single or dual op-amps can be used here (for example, KR1426UD1). The node on the DA2 chip can be replaced with a similar one on the K174UN18 chip in its typical inclusion, and the microcircuit stabilizer - KR142EN5A. Diodes VP1 and VD2 can be KD 10ZA.

Microphone capsule - electret type MKE-3. as a loudspeaker, you can use sound dynamic heads with a power of 0,1 ... 0,5 W with a voice coil resistance of 8 ohms - 0,25GDSH-3, 0,5GDSH-1.

Author: G. Cattley

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