Fax machine - printer and scanner. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Fax machine - printer and scanner. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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This article describes a device that connects a computer modem to a fax machine and allows it to be used as a printer and scanner. In this case, no changes are made to the fax machine - it retains all its functions.

A fax machine (telefax) is an obligatory attribute of a modern office. By its structure, it contains both a printer and a scanner. It would seem that they can be easily used for their intended purpose. However, the fax machine is a highly specialized device. It can only be connected to a telephone line.

A computer equipped with a fax modem (they are all modern modems) can work with a fax machine as a printer and scanner only through a PBX. In institutions, for this, they use a local automatic telephone exchange, and if it is not there, even a city one. Of course, this is very inconvenient and leads to an unjustified load on the PBX. Only recently have universal fax machines with computer ports appeared, and therefore they can work not only as faxes, but also as scanners and printers. True, such devices are still too expensive and not widely used.

Readers may wonder: why print with a fax machine when the office usually has a laser printer that prints at higher quality? First, we note that the print quality of a fax machine is in many cases quite acceptable, and the cost of consumables is less than that of a laser printer. Thus, the fax machine can be used as a backup printer, which can significantly reduce the load on the main printer.

The device shown in fig. 1 is for connecting a fax machine to a computer.

Fax machine - printer and scanner

When developing this circuit, it was decided to abandon the generation of ATS response signals, so the device turned out to be simple and can be assembled even by novice radio amateurs.

Subscriber devices (AU) are connected to the telephone sockets XS1 and XS2, one of them is a modem, and the other is a fax machine. Resistors R1 - R4 simulate the resistance of the automatic telephone exchange and the telephone line, capacitors C1 and C2 connect the subscriber devices by alternating current. To power the device, a voltage of 48 V is required, which is standard for foreign devices and sufficient for normal operation of domestic ones. The power supply circuit is shown in fig. 2.

Fax machine - printer and scanner

When the AU is in the online state (the handset is off), a normal conversational current of about 30 mA flows through it. The common wire of the device is connected to the third pin of the XP1 network connector, which must be connected to a solidly grounded neutral through a power cable.

Network transformer T1 - industrial production - TP-12-14. It has two identical secondary windings with an output voltage of 18 V each. The diode bridge of the VD1 rectifier can also be with indices V-D. Instead, you can use rectifier diodes with a permissible reverse voltage of at least 100 V, a direct average current of at least 100 mA and a pulsed current of at least 1 A.

The device uses MLT type resistors. They can be replaced with others, but the power must not be lower than that shown in the diagram. Capacitors C1 and C2 in fig. 1 - K73-16V or other non-oxide ones with a capacity of at least 2 μF and an operating voltage of at least 60 V. If a transformer with one secondary winding is used, the operating voltage of the filter capacitor must be at least 80 V.

Zener diodes VD2 and VD3 can be replaced by KS224Zh, KS508D, 2S524A or one imported zener diode V7X55S47. Transistor VT1 will be replaced by KT8130V. Its feature is a large current gain. In the absence of transistors of this type, a composite emitter follower on transistors KT502D and KT814G is used.

Transistor VT1 is mounted without a heat sink, since the power dissipated on it does not exceed 1 W.

Be sure to connect the common wires of the described product, fax machine and modem (or computer with internal modem) securely. This is most easily achieved when all devices are powered from a line of three-pin euro sockets connected in parallel. The connection of the common wires to each other and to the ground wire in this case will be carried out through the grounding contacts of the sockets. Otherwise, such a connection must be provided, for example, with a MGSHV wire. It is desirable that all devices are powered from the same phase of the mains.

Consider using a fax machine as a printer. Modern fax programs for Windows 95/98, such as WinFax or FaxLine, form a so-called "fax printer" when installed. In any program that allows printing a document, for example, in WinWord, select the "Print" command from the "file" menu. In the dialog box, in the "select printer" line, you need to select this particular "fax printer". When the "Print" command is executed, an additional window appears in which you need to enter the connection parameters, including the phone number, which in this case can be arbitrary. Dialing is indicated by clicks of the modem's dynamic head. After dialing the number, lift the handset of the fax machine and press the "Start" button. In this case, the computer will transmit the document via modem, and the fax machine will receive and print it.

To use the fax machine as a scanner, you must run a fax receiving program on your computer. Load a document into the fax machine, dial an arbitrary phone number and press the "Start" button. At the end of dialing, the computer is given the command to "receive fax". The modem will "pick up the phone" and send a signal to receive the document. After that, the fax machine will start scanning and transmitting the document, the modem will receive it, and the computer will write to the hard disk.

If you cannot print or scan, you will need to check the program and fax machine settings. In particular, such settings of the fax machine are possible when it will not print the document, but will place it in its memory, from which it can later be printed. Also, when scanning a document, it can be placed in the memory of the fax machine. In this case, the document can be transmitted later.

Since the device does not generate response signals, in all settings you need to disable the option "recognize PBX response signal".

Author: M.Evsikov

See other articles Section Telephony.

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