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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING How to replace the counter KR531IE14?. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer In the process of acquiring a set of necessary components, I suddenly had to face the lack of sale of the KR531IE14 counter, which is part of a good half of the frequency counter designs. It is at its input that a signal is fed from the output of the amplifier-shaper. The popularity of this asynchronous decimal counter is due to its ability to handle input pulse trains up to 80 MHz. You can, of course, replace this counter with a similar one from the K555 series, but it's a pity to lose the speed of the frequency meter. There is a way out, however. The market is now inundated with counters KR531IE16 and KR531IE17, and at very low prices. This stimulated attempts to use at least one of them instead of KR531IE14. Consider a fragment of the counting unit of the frequency meter on this counter (Fig. 1).
Pulses with a steep front and decline are fed to the input C1 of the counter operating in the counting mode (at the inputs R and L - high level). Switching occurs on a negative voltage drop. At the outputs 1,2, 4, 8, the counter generates a BCD pulse sequence, since the output 1 of its first trigger (forming a divider by 2) and the clock input C2 of the remaining three triggers (a divider by 5) are interconnected. At the moment when input L goes low, the information (provisional code) present at inputs D1, D2, D4, D8 is synchronously loaded into the counter triggers and displayed at the outputs. And since the outputs are connected to the corresponding inputs, the counter displays "itself", i.e., the counting stops in the entire counting line (the K531IE14 counter in the frequency meter is usually followed by six or seven K555IE6 counters). Upon completion of all processes - writing information to registers, displaying an indicator on the display - the frequency meter generates a short low-level pulse that enters the input R of the counter and resets it. Following this, a high level appears at the inputs R and L and the counting cycle repeats. The KR531IE16 counter (Fig. 2) is also a four-digit BCD counter, but it has a different operating logic. UD input counting direction switching signal input; at a high level, the account goes to increase, which is required.
The counter is switched by a single (positive) voltage drop of clock pulses, and not by a negative one, like in KR531IE14, but this does not play a role in our case. Switching occurs when the EL input is high and the EP input is low. If a high level is applied to the EP input, the count stops. The counter KR531IE16 also has a drawback - the absence of a reset input. However, this difficulty can be easily bypassed if a low level is applied to the EL input, with the arrival of the next single drop to the input C, information from the inputs D1, D2, D4, D8 connected to the common wire will be written to the counter, which is equivalent to resetting the counter. It occurs with a small delay, equal in the worst case to the pulse repetition period. At a frequency of 1 MHz, the delay will not exceed 1 µs from the moment of switching the parallel loading input of the EL counter. All this allows you to use the counter KR531 IE 16 instead of KR531IE14. As can be seen from fig. 2, the parallel download enable signal must be inverted. Usually, several NAND elements remain free in the frequency meter, one of which can be turned on by the inverter. If in the frequency meter this signal was already inverted with the previous counter, then the DD2.1 inverter is not needed, and the output 10 of the counter is connected directly to the desired point. In extreme cases, the inverter can be assembled on a transistor according to the circuit shown in Fig. 3.
A few words about the constructive side of the matter. The KR531IE16 counter has sixteen pins, so when installing it on the board, only soldering the power circuits and bending free pins will not be enough. You will have to drill two additional holes and cut all the conductors coming to the old meter, except for one power wire. You can solder short conductors to the pins of the microcircuit and, passing each one into the corresponding hole, solder it. The ideal, of course, would be the option of wiring for a new node at the design stage. The frequency meter I made after the indicated alteration provides registration of frequencies up to 60 MHz. I did not conduct experiments on the selection of copies of the counter. After warming up, this limit decreased to 59 MHz. By the way, measures to remove heat from the meters (and other microcircuits of the KR531 series) would not be superfluous. Author: A.Krotov, Baranovichi
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