Ok, one simple step which might help you to get going. So far so good. You can easily extend the USB with passive expansion cords, as well as with active USB expansion cords, easily getting an extra 30m. Of course it is not an RS, but comes at no further thinking.
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It supports up to 2. You can think of RS as RS on steroids. The data starts out as typical TTL level serial as far as the microcontroller is concerned while the RS module takes care of converting the electrical signals between TTL and the differential signaling used by RS This works by passing the bus through each device where it picks off the signal as it passes through as shown below.
Since they all share the same bus, to avoid conflict the Slave devices only talk when they are asked for something by the Master such as requesting a temperature reading. Differential Signaling The RS uses differential signaling and requires only 2 wires and a common ground. Differential signals operate by putting the signal on 1 wire and the inverse of the signal on the other wire.
This improves the signals noise immunity and the ability to recover the signal at the far end of the cable as noise tends to couple into both lines equally and therefore cancels out at the receiving end. On the module, these are available on the screw terminal block as well as the two center pins on that end of the module.
When connecting the modules together, the wiring is straight through, so A on one end should be connected to A on the other end and B connects to B. The wires should ideally be twisted pair. Using twisted pair becomes more important for longer runs or where there is a lot of electrical noise. For simple breadboard testing or other short runs, it is not necessary. A common ground is needed, but this can often be provided by the earth ground at each end for shorter runs.
Network cable is often used for connecting RS as it provides twisted pair, plus it can provide a ground wire as well. Pull-up Resistors The module provides four 10K pull-up resistors on the data lines. These pull the lines to a known state when data is not being transmitted. Finally there is a single ohm resistor R7. If using in a multi-drop configuration, the modules on the two ends of the line should keep these resistors. Modules in the middle of the line should have these resistors removed to prevent loading the lines too heavily as shown in the pic above.
This requirement can often be ignored when the number of devices is small. Module Connections The module has two 4-pin headers on the assembly. Active LOW. Connects to a digital output pin on a microcontroller. Typically jumpered to RE Pin. When working with these devices, keep in mind that they are basically just level translators. From the microcontrollers perspective, the functionality is the same as if two RS serial ports are connected for communicating between the devices.
If there is difficulty in using the devices, they can often be temporarily removed from the setup to see if the issue is with the RS or something more basic in the setup. This timing can be affected by the data rates being used.
If you are getting garbage transmitted, this is usually the first place to look. The programs below create both a Master device and a Slave device. For this setup, you will need two Arduinos of any type or other microcontrollers and two of the RS modules. You will download the Master software to one device and the Slave software to the second device.
The programs use the SoftSerial library for communication in order to leave the hardware serial port available for monitoring the data on the Serial Monitor windows of the two Arduinos. If you are using a version of board that has multiple hardware serial ports, you can use one of those instead if you prefer but it is recommend to get the setup up and running as shown first, then start making mods. Both devices use the same pins for their soft serial port. You can use either the terminal block or the header pins to make these connections.
The Master device allows you to type any character in the top portion of the Serial Monitor window and once you press enter, it will send that character to the Slave device. When the Slave receives the character, it will send what it received out to its own Serial Monitor window as well as echo it back to the Master device. Once the Master device receives the character back from the Slave, it will print it out to its own Serial Monitor window.
To do that, you just need to open the IDE from the Start menu or where ever you typically open it twice. You cannot just open a 2nd window from an existing IDE. Once you have two separate IDEs running, open the Master software in one and the Slave software in the 2nd.
Configure both for the COM port and the Arduino type you are using with each window. This code runs on the first Master device. Just redefine them below. This code runs on the second slave device.
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