Refinement of caller ID on Z80. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Telephony

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Many radio amateurs remember what a boom caused a novelty seven years ago - telephones with caller ID, called "Caller ID on the Z80". Time has passed, new superphones have appeared, far superior in capabilities to their predecessor. However, many still have the good old AONs that still work normally, and there is no point or desire to part with them, especially if the device is assembled by hand. But it still needs some improvement. This will be discussed in the proposed article.

This device has several "pain points". One of them is the so-called "hanging" of the processor system. What consequences this leads to, the owners of AONs on the Z80 are well aware. True, if the "freeze" occurs every 2 ... 3 months - this is quite normal. "Hanging" every five minutes should already be considered a malfunction. When the processor executes a prescribed sequence of instructions, then an error in reading just one bit leads to a violation of this sequence. The specific causes of failures may be different, for example, impulse noise.

The processor cannot exit the hung state on its own; for this, an external reset signal must be applied to it or, as they say, the processor must be restarted. There are two reset devices in AON - initial at power-up and forced (regeneration) performed on one of the channels of the KR580VI53 timer. However, the operation of the forced reset device turned out to be unreliable, since reset signals are properly formed only when the processor system is operating normally, i.e., when they are not needed at all.

On fig. Figure 1 shows a diagram of a simple auto-regenerator unit, the connection of which to the AON on the Z80 allows not only to quickly "reset" freezes, but also ensures that the processor is reset when the mains power is turned on.

(click to enlarge)

The basis of the device is a retarded multivibrator based on elements DD1.1 and DD1.2. Two serially connected inverters DD1.3, DD1.4 are connected to the output of the multivibrator and act as a buffer amplifier. During "freezes", rewriting pulses almost always disappear, which in a normally working device come from the output of the DD6.3 element (according to the telephone circuit with AON in the article "Businessman's Phone" - "Radio", 1993, No. 9, p. 33). The overwrite pulses have a duration of 0,5 µs and a repetition period of 8 µs. The absence of these pulses is a signal of "freezing".

From the AON board, the pulses arrive at the detector with voltage doubling (elements VD1, VD2, C2, R1). From the detector, a high level goes to pin 2 of the DD1.1 element and slows down the multivibrator. The DD1.4 output is also high, the VD4 diode is closed and the device does not affect the processor.

When the pulses disappear, the capacitor C2 is discharged and, as soon as the voltage reaches the switching threshold of the element DD1.1, the multivibrator starts to work. At the output of element DD1.4, a low-level pulse with a duration of 0,1 ... 0,15 s appears, which resets the processor. If normal operation of the processor part is not restored within 1,5...2 s, the reset cycle is repeated.

The need for a relatively long pause is due to the fact that in some versions of the programs, when the device is connected to the network, a short melody sounds, and only then information appears on the indicator.

If the pause is shorter than the background music, it will not be possible to start the caller ID when the power is turned on. When determining the number, all the "forces" of the processor go to perform this operation and the indication stops - a rectangle is displayed in the first digit of the indicator. The discharge time of the capacitor C2 must exceed the number determination time, otherwise it will be perceived as a "freeze". With the ratings indicated on the diagram, the discharge time is 3 ... 5 s.

The device is mounted on a printed circuit board made of one-sided foil fiberglass with a thickness of 0,75 ... 1 mm. The PCB drawing is shown in fig. 2. All resistors and diode VD1 are mounted vertically. Jumpers are made with PEV or PEL wire. In the phone case, the block is mounted in any convenient place; for this, a free area on the board is provided. It is desirable that the connecting wires have a minimum length. On the AON board, you need to remove the elements of the processor initial startup circuit (VD12, VD13, C4, R20) and the forced regeneration connection circuit (VD14).

Chip DD1 can be replaced by K176LE5. Capacitors - any small-sized, for example, type KM. Since domestic resistors MLT - 0,125 are produced with a resistance of up to 3 MΩ, imported resistors are used in the device. It is permissible to use several resistors MLT - 0,125 connected in series. You can also get the right time by using larger capacitors C2 and C3 with a proportional decrease in the resistances of resistors R1 and R3.

The device does not require settings, but due to the significant variation in the capacitance of ceramic capacitors, you should check the duration of the pulse, pauses and the discharge time of capacitor C2. If they turn out to be significantly less than the nominal values, you need to select capacitors C2 and C3.

As experience shows, the introduction of an additional SB button for manual processor reset simplifies the use of the device - with its help, you can exit most modes into the main one without hesitation. In devices assembled in the VEF case, you can use the existing microphone mute button.

Perhaps your device, which worked fine at the beginning, over time, more and more often began to fail, "freeze". The main reason for such troubles is bad contacts - it is not for nothing that they say that electronics is the science of contacts. Contact defects are divided into three groups - poor plating of board vias, poor-quality (so-called "cold") soldering, and poor contact in panels on which microcircuits are installed. The first defect is almost completely revealed during the installation and adjustment of the device, the last two manifest themselves over time. Finding and eliminating 2 - 3 cold solder joints is a feasible task, but if there are more than 10 of them, it hardly makes sense to spend time on this.

Domestic sockets of old releases, even with gold-plated contacts, do not provide a reliable connection. And if such panels are installed in your device, then first of all you should replace them. A ROM chip is almost always installed on the socket and very often a processor. As experience shows, the ROM chip is the most sensitive to the quality of contacts, and its socket must be replaced first. It is best to use sockets with collet contacts.

When dismantling the panel, the main task is not to damage the printed circuit board, otherwise the subsequent repair will be difficult and time-consuming. You should not try to remove the socket with a soldering iron with a group tip or with the help of solder suction - these methods do not guarantee the absence of damage. Another way is more reliable. With a sharp knife, carefully break off the sides of the socket so that the contacts are left without mechanical fastening. Then, heating the mounting holes with a soldering iron, the contacts are removed one by one from the board with tweezers. This must be done without excessive effort, otherwise you can tear off the conductors from the side of the socket, and if the leg "does not work", it is better to wait a bit until the solder in the mounting hole has completely melted. After removing the contacts and removing the panel housing, it is necessary to prepare holes for installing a new panel. To do this, the contact pads are heated with a soldering iron and a sharply sharpened match inserted into the hole from the side of the parts removes the solder residues from the hole. After that, install and solder a new socket. This method ensures quick removal of the socket without damaging the printed circuit board.

The resistance of the resistor R2 does not have to be so large - 10 kOhm is enough. It is better to switch the lower output of the resistor R4 to the output of the DD1.3 element, while the operation of the multivibrator will be more stable.

Author: D.Turchinsky, Moscow

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