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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Improvement of the SEC-850M receiver. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception We bring to the attention of radio amateurs an updated version of the VHF-FM receiver firmware already with the name "SEC-850F" (Full version). This version is a correction of the version of the initial modification "SEC-850M", which were noticed by the author during a thorough and detailed check, as well as the addition of a number of service functions: - Watch. - Temperature meter (2 pcs.). - Changed the advertising screensaver when turning on the receiver - instead of displaying the letter-by-letter right-to-left smooth appearance ("entry") of the inscription "SEC850" in the previous version, the entry "SEC850F" is now installed on the indicator screen. - Introduced the function of recording from the remote control audio adjustments on the current recorded channel. When you press the "M" ("record") button on the remote control, audio adjustments are automatically recorded on the currently recorded channel, while the indicator screen displays from left to right a dynamic bar "- - - - - - - - - - - - - - -" activating the recording mode. At the end of recording, the current mode data is restored on the indicator screen. If the frequency is set directly and the data is not recorded in the EEP-ROM (the current channel is not recorded), then when you press the "M" button on the remote control, the current data and settings will be automatically written to the last channel (channel 40). To avoid conflict situations in the frequency dialing and channel recording mode, the "M" recording button from the remote control is blocked. When recording a channel, the position of the channel number is corrected (the first significant index "0" of the channel number disappears, except for the zero channel). - Introduced the display of the number of the zero channel (in the previous version, the number of the zero channel was not displayed and therefore there was no difference between the indication of the zero channel and the frequency, the data of which was not recorded in EEPROM). When decreasing or increasing the frequency, the number of the current channel does not disappear. - By pressing the button "?" (manifestation of hidden teletext information) The remote control in the main mode (frequency display mode) for 3 seconds displays the firmware version number "U 2.1b" - version 2.1 beta. - Significant changes have affected the operation of the receiver in the UHF mode (operation from an external signal source at input 1 of the audio processor). For more efficient switching of the receiver from the main mode to the UHF mode, by pressing the button "9" of the control unit (control unit) or "I" (calling the teletext index page) of the remote control, the operation of the audio processor on input 1 and 2 in "Stereo A" modes is excluded and "Stereo B". In the event that we enter the UHF mode on a channel whose data is not recorded in EEPROM, after 3 s the inscription "In1 St" is displayed (input 1 of the audio processor, "Stereo" mode) the inscription "PA _ - ~" appears (power amplifier, further symbols of pseudographics of the UZCH mode). When you press the "M" button on the remote control, the current data of the ULF mode and settings will be automatically recorded to the last channel (40th channel). If we enter the UZCH mode on the saved channel, after 3 seconds the inscription "1p1 St" is displayed, the inscription "RAZZ _-" appears (power amplifier, 33 - channel number, then UZCH mode pseudographic symbols). When you press the "M" button on the remote control, the current ULF mode data and settings will be automatically recorded to the current channel (in this case, the 33rd channel). You can delete a channel only in the main mode (frequency display mode). - To avoid conflict situations in the UZCH mode, some of the control buttons are blocked, with the exception of the audio function control buttons, channel switching buttons, the reset button "Esc", the button to turn off the dynamic indication "Network", the mute button, the button for selecting the audio processor input selector "I" of the remote control "9" BU, record buttons "M" RC. Service modes This version implements the following service modes: clock, thermometer 0 and thermometer 1. During the initial initialization of the program, connected external devices (clocks and temperature sensors) are polled. In the absence of these devices, the call from the remote control panel of the corresponding service modes (clocks and temperature meters) is blocked. To re-initialize the program, just press the "Esc" button on the remote control. Exit from the service mode to the main mode occurs by pressing the corresponding button to call the current service mode. Service modes are switched among themselves (except for the technological mode of clock setting). In the service mode, some of the control buttons are blocked, with the exception of the buttons for selecting and controlling the corresponding service mode, the reset button ("Esc"), the button to turn off the dynamic indication "Network", the mute button. When entering the service mode, the indicator screen displays a dynamic bar "- - - - - - - - - - -" converging to the center of the activation of the service mode, then the data of the current service mode is displayed. Thermometer The temperature meter is implemented on a DS1621 chip (Dallas Semiconductors). Brief information about the DS1621 chip:
On fig. 1 shows the circuit for connecting the temperature sensor chip to the receiver.
The temperature sensor 0 is called when you press the "teletext mixing mode" button on the remote control, and the temperature sensor 1 is called when you press the "teletext mode on" button on the remote control. At the same time, after displaying the dynamic bar, temperature data "0 25,0 °С" appear on the indicator screen (0 - temperature sensor number, 25,0 °С - current temperature value). It is not allowed to disconnect "on the go" thermal sensors, since after the subsequent connection, the microcircuit must be reinitialized (to re-reinitialize the program, just press the "Esc" button on the remote control). Due to the fact that sometimes the question arises of providing the necessary thermal conditions in the final design of the receiver, and not only, a forced cooling circuit is implemented on the basis of the thermostat function (Fig. 2).
This version implements the functions of a thermostat (for both temperature sensors) with software hysteresis values in the range of +40 °С...+30 °С. When the temperature reaches +40 ° C, a low-level voltage appears at pin 3 of the DD1 microcircuit, the transistor VT1 closes and the high-level voltage opens the transistor VT2, thereby turning on the M1 fan motor. Further, in the case of cooling to a temperature of +30 ° C, a high-level voltage appears at pin 3 of the microcircuit, which leads to the fan turning off. Each reader can perform the final fan control cascade according to his own scheme from improvised components. Watches. The clock is implemented on the Philips PCF8583P chip. Brief information about PCF8583P: - basic operating modes - clock with synchronization from the internal generator (f = 32768 Hz); - clock with external synchronization (f = 50 Hz), pulse counter; - supply voltage range-1,0...6,0 V; - consumption current - 200 μA. The main functions when the microcircuit is in clock mode are clock (display hours, minutes, seconds, hundredths of a second), calendar (display days, months, days of the week and years), alarm clock and timer (with the ability to program the functions of the alarm clock, timer and interrupt system ). This version implements a clock (full and short format), a calendar and an alarm clock. On fig. 3 shows a diagram of connecting the microcircuit to the receiver.
In connection with this refinement, it is necessary to disconnect pin 3 of the 3DD1 (EEPROM) chip in the control module A3 of the main receiver unit from the common power bus and connect to + 5V, and connect pin 3 of the DD1 chip (clock) to a common conductor. The following types of EEPROM can be installed in the control module: AT24C04, AT24C08 (Atmel) or compatible with them from other manufacturers. Diodes VD1, VD2 are used for power decoupling. Capacitor C1 is necessary to protect against the influence of transients in the event of a loss of the main power supply and inclusion in the standby power mode. The charge of this capacitor is enough to run the clock for about 5 minutes, during which there is no power. During this time, it is quite possible to have time to replace the discharged backup batteries without resetting the clock. The bell device is made on a transistor VT1, a resistor R3 and a sound emitter B1. The call of the clock mode occurs when you press the "set timers" button on the remote control. At the same time, after displaying the dynamic "band", the clock readings appear on the indicator screen in a shortened format (without displaying seconds) - "12-.00". Simultaneously with a frequency of 1 Hz, the delimiter cursor blinks (if the alarm is activated, the decimal point of the alarm mode activity blinks in the delimiter cursor segment). Calling up the clock in a shortened format occurs when you press the "red" teletext button on the remote control. Calling up the clock readings in full format (with displaying the readings of seconds) occurs when you press the "green" teletext button on the remote control, while the readings are displayed on the screen - "12-00-.00". Calling up the calendar readings occurs when you press the "orange" teletext button on the remote control, while the screen displays "dt 28-.07" (where 28 is the day and 07 is the month). Calling up the alarm clock occurs when you press the "blue" teletext button on the remote control, while the screen displays "AL 06-.30" (where 06 - hours, 30 - minutes). Turning the alarm on/off occurs by subsequent pressing this button. Clock adjustment modes. Using the remote control, select the desired clock mode (clock, alarm or calendar), press the "Ok" button on the remote control and enter the setting mode. At the same time, the current clock readings begin to flash on the screen in the leftmost position with a frequency of 1 Hz. Using the "P+" and "P-" buttons on the remote control, the adjustment position is selected, and using the "+" and "-" buttons on the remote control, the selected reading values are increased or decreased. Subsequent pressing the "Ok" button on the remote control will exit the setup mode and turn on the DD1 chip. Please note that the internal counters are temporarily stopped during the setting mode! But when you press the button "fixing the current teletext page" on the remote control, the seconds are corrected, and you do not need to enter the adjustment mode. Alarm modes Work alarm clock in clock mode. When the alarm goes off, the dynamic display will turn on. If it was turned off before (this mode is very convenient at night, there is no eye irritation on the indication), the sound on the current channel is turned on (if it was turned off) and the sound generator tone is modulated at a frequency of 1 Hz. The alarm is turned off by pressing the mute button on the remote control, while the alarm function does not need to be reinitialized (the next alarm will be at the same time until it is turned off in the clock mode with the "blue" teletext button on the remote control). The operation of the alarm clock in the main mode (receiver mode). When the alarm goes off, the sound generator will sound continuously (in this mode, to prevent the I2C serial bus from affecting the receiving part, the clock chip is not constantly polled. In the previous case, when the alarm goes off, the clock device is programmatically switched to the intermittent sound mode). The alarm is turned off by pressing the mute button on the remote control. If the alarm goes off when the main power of the receiver is turned off, approximately 0,5 s (processor reset time) after the receiver is turned on, the sound generator signal is forcibly turned off. During the construction and operation of a large number of receivers, some simple improvements were made to improve the performance of its analog part. 1. After the submodule of the additional filter, we recommend installing another single piezo filter in a "chain". There will be three filters in the IF path in total. This solution is often used in high-end imported car radios. Its input must be connected directly to the output of the A1.2 module, and the output to pin 18 of the 1DA2 chip. Structurally, this can be done as follows: install the filter in the place where the 1R6 resistor stands vertically. Put a new filter (output and common) in the holes for this resistor. Connect the filter input to the jumper that is on the printed circuit board; for this, one end of it should be unsoldered and unbent. In this case, the 1R6 resistor is installed from the bottom of the board, directly to pins 17 and 18 of the 1DA2 microcircuit with a conventional or chip element. It is advisable to use L10,7A type filters from the same batch (since they have a smoother phase response), which has a positive effect on stereo reception. With filters like 10,7S (even with two), stereo distortion can already be observed. The additional attenuation introduced by the new filter even has a positive effect on the operation of the IF path made on the K174XA6 microcircuit - its operation is somewhat facilitated under conditions of a high level of the 2nd IF signal. At the same time, the previous gain of the IF path, necessary for the operation of the AGC and SHP system, does not change, since the signal for them still goes after the 2nd filter. But now it is better to take the IF signal for submodule A1.3 after the 3rd filter. With this refinement, the receiver has a higher sensitivity and selectivity in the adjacent channel. Specially new measurements were not carried out, but even subjectively the receiver began to receive most of the city stations with little or no antenna, only on the SLE antenna connector. Previously, a modulated 100 MHz signal at a level of 2 μV applied to the input of the receiver could be clearly distinguished from the noise by ear, but on the oscilloscope, the low-frequency signal was practically smeared with noise. After refinement, even with an input signal level of 1 μV, the demodulated audio frequency sine wave retains its shape well. 2. In some instances of the RF module in the device on the 1DA1 chip (oscillator 21 MHz), parasitic self-oscillation was observed not at a frequency of 21 MHz, caused by the high inductance of the 1L2 tuning coil. We recommend installing a jumper instead of it, and adjusting the frequency of the 1BQ1 quartz resonator to produce capacitors 1C5, 1C6, 1C8. With such a resonator that we use, we got the following capacitance values: 1C5, 1C8 - 47pF, 1C6 - 100pF. In this case, the frequency mismatch is no worse than ±2 kHz. Unfortunately, there were errors in the printed circuit boards and circuit diagrams in the article. The authors apologize to readers and recommend paying attention to the following. 1. On the diagram of module A1, you should swap the input / output numbers of the 1DA3 microcircuit. 2. On the printed circuit board of the A1 module (Fig. 3), there is no connection between the pads of the lower terminals of the elements 1C27 and 1L8. 3. On the printed circuit board of module A1.2, resistor R2 is not marked, there are contact pads for it. 4. On the printed circuit board of the submodule A1.3 (Fig. 7), there are no connections between the pads of the left terminals of the resistors R8 and R11, adjacent terminals of the resistors R1 and R2, the anode of the VD1 diode and terminal 12 of the DA1 microcircuit. 5. On the circuit diagram of module A2, the 2DA2 chip does not have pin numbers 2 (to the 2C24 capacitor) and 4 (to the power plus). Capacitors 2C35 and 2C36 should be 47 uF each. 6. On the printed circuit board of the A2 module (Fig. 9), the pads and the track of pins 1, 2 and 3 of the 2DA1 microcircuit should not merge (their wiring corresponds to the circuit diagram). 7. On the printed circuit board of module A2, there is no connection between the pads of the ungrounded terminals of the capacitors 2C22 and 2C25, the pad of the middle terminal of the resistor 2R3 is not connected to the pad of the right output of the same resistor according to the figure. 8. On the printed circuit board of the A3 module (Fig. 11), there is no contact pad at the left output of the 3VD4 diode according to the figure. The lower right pad of the 3SA1 button must be free. 9. On the power module diagram (A4), the main variant of the 4DA2 chip should be UC3842, and its replacement should be UC3844. The ratings of the 4R7 and 4C4 elements indicated in the diagram correspond to the UC3842 use case. For the UC3844 chip, the values of the parameters of the elements should be 5,6 kOhm and 4700 pF, respectively. 10. On the diagram of module A4, you should change the position number of the capacitor 4C15 - 470 uFx25 V, it should be 4C14. On the printed circuit board (Fig. 14) everything is correct. 11. On the printed circuit board of the A4 module (Fig. 13), between contacts 1 and 2 of the 4DA2 microcircuit, the reference designation 4C3 should be replaced with 4C5. 12. The inductor 4L1 of the A4 module is wound on a "dumbbell" made of M2000NM ferrite. Winding is carried out with a PEV wire with a diameter of 1 mm in one layer. The inductance of the inductor should be 10 ... 15 μH. In the process of communicating with radio amateurs, it was found that many people who repeated the receiver have interference from dynamic indication. There are several ways to eliminate them. 1. Shield the KSS wire from the RF module to the stereo decoder input (and connect to the common wire on one side). 2. Make a few additional "common" conductors from the RF module to the AF module. The same should be done from the control module to the AF module (it also helps, but not always). Connection points must be selected empirically. 3. When mounting into a housing, it is desirable to place the boards in such a way as to place all low-signal circuits (LA3375 and KR544UD2 inputs) away from the control unit. 4. The loops going to the control modules and AF should be made shorter (as far as possible) and it is better to shield them by passing them into the braid. 5. You can reduce the pulse current of the indication by selecting resistors 3R8 - 3R15 (but not to the detriment of the brightness of the indicator). This is especially true for red glow indicators (TOT3361AN), since they have a lower voltage drop across the segments (respectively, a larger current through the segment) and greater brightness. 6. The "quiet reception" button on the remote control (Power) also helps, which turns off the indication, and there will be no interference from the indication at all. But this is for the last resort. Based on the experience of using various types of VCS, I would like to recommend the use of only selectors built on the basis of the TSA5522T(M) frequency synthesizer chip. Of those known to us, these are SK-V-362 D, KS-N-132, 5012FY5, 5002RN5. The synthesizers of these SCRs have minimal phase noise and are excellent for narrowband reception and the receiver as a whole. In an extreme case, if high-quality reception of narrow-band stations is not required, you can use VCR based on synthesizers of the TSA5526, TSA5527 types or microcircuits of the TDA6402, TDA6502 types combined with VCOs - these are selectors KS-H-134 O (Selteka), KS-H-136 O (Selteka), KS-H-144 O (Selteka), UV2051A-CWP (Wittis), 6012PY5 (Temic), SK-V-562 (Vityaz) - but you will have to abandon the narrowband receiver function, since these microcircuits have a large phase noise and their VCOs "walk" within ±3...5 kHz of the fundamental frequency. Broadcast and TV reception will not be affected, and reception of stations in the narrow IF band will become difficult. Let me remind you that to use these channel selectors, you need a program correction. Author: V.Sazonik, Vitebsk, Belarus
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