A variant of the VHF receiver control unit with a frequency synthesizer on the LM7001 chip. Scheme, description

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A variant of the VHF receiver control unit with a frequency synthesizer on the LM7001 chip. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / VHF antennas

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Descriptions of VHF FM radio receivers with frequency synthesizers and LED or LCD indicators are published in "Radio" [1, 2]. The control unit of these radio receivers can be simplified and its efficiency increased if a pointer measuring device is used to indicate the frequency, and only a mechanical encoder is used from the controls. This set of components is sufficient to provide frequency tuning over the entire range, and to estimate the frequency on the indicator by the proportional deviation of the arrow. Practice has shown that this method of control and indication is quite attractive and convenient.

A variant of the VHF receiver control unit with a frequency synthesizer on the LM7001 chip
Fig. 1

The diagram of the control unit is shown in fig. 1. Its basis is the DD1 microcontroller. Frequency tuning is carried out by a mechanical incremental encoder S1. Information about the last setting is stored in the non-volatile memory of the microcontroller when the power is turned off and is automatically loaded when it is turned on again. The RA1 microammeter serves as an indicator of the tuning frequency. The indicator scale is linear, which makes it easy to calibrate and allows you to get high tuning accuracy.

A variant of the VHF receiver control unit with a frequency synthesizer on the LM7001 chip
Fig. 2

All parts, except for the microammeter, are mounted on a printed circuit board (Fig. 2) made of one-sided foil fiberglass 1,5 ... 2 mm thick. The encoder is mounted on the side of the printed conductors. The appearance of the mounted board is shown in fig. 3.

A variant of the VHF receiver control unit with a frequency synthesizer on the LM7001 chip
Fig. 3

Fixed resistors MLT, S2-23, tuning multi-turn - 3296W or its domestic analogue SP5-2V6 are used. The oxide capacitor is imported. We replace the PIC12F629 microcontroller with the PIC12F675 microcontroller, and for each of them there are "firmware" codes. The PEC12 encoder can be replaced with a PEC16 or EC11 encoder, provided that the wiring is correct. The values of resistances and capacitors may differ from those indicated within ± 20%. The device can be used with a pointer indicator with a full deviation current from 100 μA to 10 mA. The value of the resistor MLT, C2-23, trimmer multi-turn - 3296W or its domestic counterpart SP5-2V6. The oxide capacitor is imported. We replace the PIC12F629 microcontroller with the PIC12F675 microcontroller, and for each of them there are "firmware" codes. The PEC12 encoder can be replaced with a PEC16 or EC11 encoder, provided that the wiring is correct. The values of resistances and capacitors may differ from those indicated within ± 20%. The device can be used with a pointer indicator with a full deviation current from 100 μA to 10 mA. The value of the resistor R2 is indicated for a microammeter with a total deflection current of 100 μA, therefore, when using indicators with a large maximum current, the resistance of this resistor must be proportionally reduced.

The tuning range of the receiver, incorporated in the source text of the microcontroller program, is 87 ... 108 MHz. However, its boundaries can be changed by changing the values of the constants in the non-volatile memory of the microcontroller when writing the program to its memory. This allows you to adapt the control unit to a specific receiver and its operating frequency range. For example, if in your region broadcasting is carried out in the range of 100 ... 105 MHz, then you can set this frequency interval. But for any range, the microcontroller output signal deflects the microammeter needle from 0 to the maximum scale division. Thus, when changing the tuning range, the scale division value will also change.

Setting up the device comes down to setting the resistor R2 arrows to the maximum division of the scale. You must first make at least twenty turns of the encoder clockwise to ensure that the maximum tuning frequency is reached.

Next, consider the method of setting the boundaries of the range in which the receiver will operate. To do this, in a program on a PC, for example WinPic800, open the "firmware" file. Then open the EEPROM tab. At addresses from 0x2102 to 0x2105, the values of the constants of the codes of the upper and lower frequencies of the operating frequency range are found (Fig. 4).

A variant of the VHF receiver control unit with a frequency synthesizer on the LM7001 chip
Fig. 4

Frequency values are presented in hexadecimal format. For example, the upper frequency corresponds to the number 2A 30 (or 10800 in decimal), and the lower frequency corresponds to 21 FC (or 8700 in decimal). For the tuning range of 95 ... 105 MHz, you must enter the values 29 04 and 25 1C, respectively.

Literature:

1. Nosov T. Household VHF receiver with digital control. - Radio, 2010, No. 6, p. 16-18.
2. Nosov T. VHF radio receiver from a car radio tuner. - Radio, 2010, No. 9, p. 20-22.

Author: G. Nosov, Saratov; Publication: radioradar.net

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