Adapter I2C-COM port of the computer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Adapter I2C-COM port of the computer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Computers

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Sometimes, especially when studying the features of a particular microcircuit or debugging a device based on it, it is convenient to connect the I2C interface lines to a computer. Since computers are not equipped with such an interface, this requires an adapter that converts the transmitted signals into an acceptable form for one of the standard computer ports.

The device is a signal level converter of the RS-232 interface (computer COM port) to the I2C bus signal levels and vice versa. The number of elements in the adapter is extremely small: one microcircuit, two transistors and four resistors and a capacitor each.

Adapter I2C-computer port
Fig. 1

On fig. 1 shows the adapter diagram. The MAX232ACSE(DA1) chip is a widely used bidirectional RS-232 to TTL level converter. Capacitors C1-C4 are the standard "strapping" of this microcircuit. Inverters on transistors VT1, VT2 provide the adapter with open-collector outputs necessary for the I2C bus, and resistors R3, R4 maintain a high level on the bus lines with closed transistors.

Adapter I2C-computer port
Fig. 2

The mounting is carried out on a double-sided printed circuit board, shown in fig. 2. It is designed to install surface-mounted elements (resistors and capacitors - size 0805) and place an XS1 socket inside the case, which is connected directly to the computer's COM port plug. Wire jumpers must be inserted into the holes with dots in the center, soldering them on both sides.

Instead of the MAX232ACSE chip, you can use the ADM232AARN and its other analogues, but you need to make sure that they are designed to work with capacitors C1-C4 with a capacity of 0,1 microfarads. Otherwise, you need to replace them with capacitors with a capacity indicated in the description of the microcircuit.

The BC850 transistors can be replaced with any other low power npn structures that have a static current transfer ratio of at least 50. The 5V supply must be supplied to the adapter from the I2C device it is working with.

A properly assembled adapter does not need to be adjusted. If necessary, it can be checked using the program described in [2]. It allows you to change the logical levels of signals at the outputs of the COM port and monitor the state of its inputs. The program can be downloaded hence.

Adapter I2C-computer port
Fig. 3

To manually control a device connected to a computer via an adapter, the i2cWin program was written, the window of which is shown in Fig. 3. It requires Windows 2000/XP/Vista operating system, 2 MB free hard disk space, free RS-232 port. To work under Windows 2000/XP, the Microsoft dotNet framework 2.0 package must be installed, which can be downloaded free of charge from microsoft.com. It is not required for Windows Vista. Instructions for working with the i2cWin program can be obtained by selecting the "Help" item in its main menu.

The PCB file of the adapter in P-CAD 2006 format and the installation file of the i2cWin program can be downloaded hence.

Literature

Semenov B. I2C bus in radio engineering structures. - M.: "Solon-R", 2002.
Long A. How to test PonyProg. - Radio, 2003, No. 5, p. 25, 26.

Author: M. Kvasnikov, Nizhny Novgorod; Publication: radioradar.net

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