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Domótica sencilla, fácil y económica

 Introduction to home automation network free microHomeLan
 Economic issues in home automation installations

1.1.4. i2c bus

i2c bus

In the central unit CPU has joined Uhlan the i2c serial communication bus two-wire bus (SDA and SCL) for communication with other peripherals such as memory circuits, I / O, A / D and D / A etc. . Giving the central unit the ability to Uhlan expand with new features.

Connectors J3 and J4 (i2cA, i2cB) consisting of RJ-11 connectors 6 wire is intended to augment the number of entries in the system using touch sensing circuitry (Uhlan touch button). The connection of the sensors can be performed using a 6-wire phone cord into an RJ-11, using the pin 1 and 2 for +5 V power supply, 3 for SDA data, 4 for the sync signal SCL and 5 and 6 to GND.

SV7 connector (i2cC) consists of 6 printed circuit poles is intended for system expansion by adding new i2c device.

The resistors R8 and R9 2K7Ω (default) are the pull-up resistors on the I2C bus.

Protection circuit

It has set up a temporary protection for any that may occur in the cables connected to the i2c bus fuses formed by resistors R11, R13 and zener diodes D3 and D4.

The fuse resistors R11 and R13 of 10Ω limits the current through the diodes D3 and D4 Zeners 5.1 V 0.5 W when a voltage surge greater than +5.1 V and -0.6 V preventing the voltage applied to the microcontroller pin exceeds the maximum specified by the manufacturer. When the current exceeds the permitted limits will melt resistance preventing the input circuit damage.

Imax_{Res}\ =\ \sqrt{\frac{P}{R}}\ =\ \sqrt{\frac{0.25}{10}}\ =\ 0,158A\ 158mA

Under normal conditions with short cables for connecting the i2c bus and domestic environments, no interference is remarkable as the protection circuit can be eliminated, in which case the resistors R11 and R13 may be substituted for ordinary resistors or a simple bridge, and diodes D3 and D4 can be eliminated.

If you want better protection diodes D3 and D4 have to change for TransZorb, Transil (transient voltage suppression diode TVS) diodes, power specially designed to protect the circuits from high voltage transients.

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