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This breakout board allows interfacing between a TTL serial line (for example the output of a discrete UART or integrated in a microcontroller)  and a RS485 bus, serial too, but with a balanced line wich has two wires referred to ground, instead of unbalanced (a conductor referred to ground) as in the classic TTL serial. For the TTL / RS485 conversion and vice versa, an integrated ST485BDR transceiver produced by ST in a SO-8 container (a sort of 4 + 4 pins for SMD) is used. The wires of the RS485 line correspond to the pins A (pin 7) and B (pin 6) and refer, on the breakout board, to the contacts with the same name. To offer maximum versatility, all lines (power supply, RX, TX, RTS of the TTL serial, A and B of the RS485) are available both in pitches on the edges of the printed circuit board and on pin-strips for insertion on other cards. Complete the circuit, the usual LD1, which indicates, turning on, the presence of power (at 5 volts because the integrated works with a single supply, in fact, of 5 volts); there is no ceramic condenser (C1) that filters the power supply line. Dimensions (mm): 22x22.


The RS485 is a simplex data communication line intended for very noisy environments (on the electric plane) and to cover long distances: up to 1.2 km. The performance in terms of electrical noise immunity and the consequent possibility of covering large distances is due to the current loop operation and to the amplitude of the data signal voltage characterizing the RS485, whose drivers (transmitter stages) produce on the two wires a differential voltage with respect to the ground, therefore, with the same supply voltage, the amplitude is twice that of an unbalanced line. Balanced means that the line sees, at each pulse, two voltages of equal amplitude but opposite polarity on the wires (A and B) of the RS485 line, which allows, in the receiver, to use a differential amplifier to add the signals algebraically, reducing theory, the disorder. In fact, by connecting the two signal wires one to the inverting input and the other to the non-inverting of a differential (for example an operational amplifier configured as voltage comparator) the signals are added algebraically, therefore when the first input is negative and the second positive the output is negative (or logical zero) while with the opposite situation at the output the high logic level is obtained. The noise picked up by the wires, which is supposed to have the same amplitude on A and B, is theoretically canceled, because what comes in from the non-inverting input is compensated with what arrives on the inverter. The RS485 is a bus because it is possible to connect in parallel to the wires of the line multiple devices, the last (the most distant) of which must be terminated with a 120 ohm resistor placed between A and B. The allowed data-rate from the RS485 it is a good 35 Mbit / s up to 10 m away and 100 kbit / s 1,200 m.

The breakout boards

The breakout boards are prototyping boards containing the already welded needed component, whose connections are carried outside the bases on easily usable connections for pitch and termination; generally the connections are pitches with a pitch of 2.54 mm, like those of the classic integrated DIP. To help those who would like to use SMD components but doesn’t have the means or the qualities to weld it, a number of integrated sensors (including sensors, switching power supplies, battery chargers, linear amplifiers, etc.) have been identified and mounted on ready-to-use bases. These breakout boards are both an aid for those who want to have ready in a traditional format the best of SMD electronics, both for those who can work with SMD components - need to have these components available on prototyping boards to apply them to circuits existing and testing, that is, to create prototypes that integrate the functions of the relative integrated, before realizing the final printed circuit of a device.


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RS485 module - mounted

  • Price: 6.60€

Tags: single phase, brainchild io, modbus rtu, uart, scada, din rail, serial, rs485 modbus

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