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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Digital code generator with memory. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception The proposed device is intended for use in radio frequency synthesizers and other devices with electronic tuning. The device has a memory that allows you to remember one hundred values of the digital code and save the information when the power is turned off.
To improve service capabilities, radio amateurs supply their radios with frequency synthesizers. An analysis of circuits published in various publications shows that devices based on microcontrollers and specialized microcircuits have the best service with a minimum number of microcircuits. However, programming microcontrollers is not an easy task. Not many radio amateurs can correctly compose an algorithm and write a program. Therefore, attempts to build frequency synthesizers on logic microcircuits without the use of microcontrollers are of interest. As a rule, they all operate under the control of a digital code generator, for example, with push-button control, described in article [1]. Unfortunately, such a device, despite the complexity, has to be tuned every time the receiver is turned on, since it does not remember any settings for the radio station, unlike a variable capacitor (KPI) or a block of variable resistors. A completely different situation is obtained if the shaper is "taught" to remember the settings made. To do this, you need to supplement it with a memory block. A description of just such a device is presented in the article. The shaper can memorize up to one hundred digital frequency codes, has a push-button setting. Recorded codes can be rewritten from one memory location to another. If there is at least one free cell, you can swap contents of any cells. The shaper is assembled on widely used and inexpensive microcircuits and requires almost no adjustment. The scheme of the proposed device is shown in the figure. It consists of several functional blocks built according to typical schemes: a tuning channel number selection block, a memory block, a control block, and the binary code generator itself. The tuning channel number selection unit is assembled on a DD1 chip containing two binary four-digit counters. One of them (DD1.1) is used to select units, and the second (DD1.2) - tens of the tuning channel number. Consider the operation of the counter DD1.1. When the power is turned on, the pulse of the charging current of the capacitor C8 creates a voltage pulse on the resistor R5, which resets the counter. Pressing the SB1 button increases the state of the counter by one. Capacitor C6 suppresses the bounce pulses of the contacts of this button. When the state "10" is reached, a current flows through the resistors R9 and R10, which creates a voltage on R5 that resets the counter. Counter DD1.2 works similarly. Pressing the SB2 button increases its state by one. Elements C7, C9, R6, R11, R12 perform the same functions as C6, C8, R5, R9, R10. The choice is made separately for tens (button SB2) and units (button SB1) of the channel number. With a large number of channels, this option is more preferable than sequential enumeration from 00 to 99. The setting channel number shows the display unit on the DD3 and DD4 microcircuits and the HG1 and HG2 indicators, included according to the standard scheme. From the outputs of the counters DD1.1 and DD1.2, the signals are fed to the address inputs of the memory chips DS1 and DS2 of the RAM block. code. In the recording mode, signals from the outputs of the shaper are fed to the same bus through resistors R12-R0, which prevent conflict. The resistance of these resistors is chosen large enough so as not to overload the counters in the counting mode, and at the same time small enough to write to the RAM cells. The code generator is a 12-bit binary reversible counter, assembled on three microcircuits of four-bit counters DD5-DD7 K561IE11, described in the article [2]. The R (zero) inputs of these microcircuits are connected, resulting in the R input of a 12-bit counter. The inputs U, C and S are connected similarly. When the shaper is in the data reception mode, the counter operates in the preset mode. Its installation inputs (D1, D2, D4, D8 of DD5-DD7 microcircuits) are supplied with the code of one of the RAM cells operating in the information reading mode, while the signal at the output of the counter is set equal to the signal at its input. In this case, the signals of other inputs (except input R) do not affect its state. Input R is used for forced zeroing of the counter in the setup mode using the SB8 button. When the shaper switches to the setting mode, the counter switches to the pulse counting mode by applying a low level to its input S. In this case, the code of the number that was before the switch remains at the output, and if it was not reset by the SB8 button, the pulse count will start from this numbers. The state of the RAM outputs does not affect its operation. The level of the signal at input U determines the counting mode: high - addition (sequential increase in the code by one with each pulse at the counting input C), low - subtraction (successive decrease in the code). Twelve bits provide a tuning step of 1/4096 of the range width, which is quite enough to fine-tune the receiver. The required operating modes of the shaper and RAM are provided by the control unit assembled on the DD2 chip. On element DD2.1, a pulse generator for counters is made. Manage it using the buttons SB3 "-" and SB4 "+". The R3C4 and R4C5 circuits suppress the bounce pulses of the button contacts. The operation of the buttons is the same, but when you press SB4, a high level is additionally applied to the inputs U of the counters DD5-DD7. With short-term (no more than 0,3 s) pressing these buttons, the generator does not work, but pulses with a frequency of pressing still appear at its output. While holding the buttons pressed, the generator operates at a frequency of about 1 Hz, which is set by selecting the resistor R8. Of course, such a frequency is too low to scan the range, so the SB5 button is introduced, which connects resistor R8 in parallel with resistor R7, as a result of which the generation frequency increases several times. On elements DD2.3 and DD2.4, a shaper control trigger is assembled. It works like this: while the shaper is in the data reception mode and the SB3 or SB4 button has not been pressed, the capacitor C11 is discharged, the output DD2.3 is high, the counters DD5-DD7 operate in preset mode. When the SB3 button is pressed, the capacitor C11 is charged through the VD4 diode, and when SB4 is pressed, it is also charged through the VD3 diode, the trigger switches and puts these counters into pulse counting mode, which is indicated by the HL1 LED. The first short press on the button SB3 or SB4 only switches the trigger, and the code at the output of the counter does not change until an increasing voltage drop comes to input C. Each subsequent press of the buttons SB3 and SB4, as well as their retention, leads to a change in the code. The trigger is in this mode until the SB7 "Back" button is pressed or the SB6 "Record" button is pressed for a long time. With a short press on the SB6 button, the code from the counter outputs will be written to the memory cell, but the trigger will remain in the setup mode. To store information, volatile RAM is used, so an internal power source is required, which is used as a GB1 battery. Since this source is low-power, and the memory chips consume a rather large current in the active mode, it is necessary to switch the RAM to the information storage mode as soon as possible when the power is turned off. This function is performed by the transistor VT1 and the zener diode VD6. As soon as the supply voltage drops to 4,5 V, the transistor closes, a high level appears at the CE RAM input (pins 18 of the DS1 and DS2 microcircuits) and it goes into information storage mode. The decoupling of internal and external power supplies is carried out by diodes VD1 and VD2. The shaper used MLT resistors, oxide capacitors imported by NOVA. Capacitor C13 should be with as little leakage current as possible. Serious attention should be paid to the choice of memory chips: according to the current consumed in the information storage mode and the minimum voltage at which its safety is ensured. The lower the values of these parameters, the better. Good results were obtained with microcircuits soldered from printed circuit boards of obsolete PCs (Et51M256A-15P from EtronTech) and end-of-life hard disk drives (W24257-A16 from Winbond). Of course, you can also use EEPROMs, which are also installed in many PC models. The main requirement for the HL1 LED is sufficient brightness at a current of about 0,6 mA. The adjustment of the shaper consists in the selection of resistors R7, R8 of the generator and resistor R15, which determines the time the trigger switches to the data reception mode when the SB6 button is pressed. If the counter DD1.1 does not automatically go to the state "0" from the state "10", select the resistor R5. In a similar case, a resistor R1.2 is selected for the counter DD6. Consider the process of setting up the shaper and writing the code to memory, for example, to cell with address 00. First, briefly press the button SB3 or SB4. In this case, the shaper will automatically enter the setting mode, as evidenced by the glow of the HL1 LED. Then you need to reset the counter DD5-DD7 by pressing SB8. Next, use the SB3-SB5 buttons to tune the receiver to the first station in the range. If you need to set up other channels, you should, by briefly pressing the SB6 button, write the received code into the cell. Then select the next cell (01) and write the code of the next station into it. If the recording of the next cell is not required, the SB6 button must be held until the HL1 LED goes out. It is not necessary to start tuning to other stations by resetting the counters: if there is already a recorded code, further tuning continues from it. Similarly, you can quickly change existing settings. If you want to return to the receive mode without writing a new code value, you should press the SB7 "Back" button. You can rewrite the code value from one cell to another (for example, from cell 22 to 88) as follows: first, in the receive mode, use the SB1 and SB2 buttons to dial the number 22. Then briefly press SB3 or SB4. Next, dial the number 88 and hold the SB6 button until the HL1 LED goes out. In the same way, you can swap the data of any two cells (for example, 33 and 55), using any free cell (for example, 99) as a clipboard. First, you need to write data from cell 33 to 99, then write data from cell 55 to 33, and write data from cell 99 to 55. Literature
Author: E. Gerasimov
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