What is Serial Communication? > 자유게시판

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The most widely used communication standard is RS232. RS485 RS-485 is a standard that allows high speed data transmission along with multiple transmitters and receivers and this makes it able to be incorporated as a network solution. You can easily enjoy the advantages such as low power consumption and long transmission range, without affording the cost of changing the sensors you are using. By adding another 2 wires, making it a 4 wires system, it allows data transmission in both directions to and fro devices at the same time, also known as full-duplex. I can run the Pi for about two hours or so on the small battery I have attached to the system and if the power does not come back on it time, then the MightyHat will automatically shutdown the Pi to prevent it from crashing due to a sudden power failure. Nothing works when this switch has been triggered and if something were to fail programmatically, no power can make it from the transformer to the sprinkler valve regardless. Simple enough. However, I didn't want to run the transformer 24x7 for no reason, so I used a relay to 1) turn on the transformer and then 2) take the 24VAC output from the transformer and connect it to the sprinkler valve.

However, if you’re looking to experiment, the latter will provide you with more versatility. Eventually the sprinklers will stop running and the pool will start to fill automatically. In a place where you are hindered by the electrically noisy environment, RS485 will be the optimal choice. Some of the examples are robotics, base stations, motor drives, video surveillance and also home appliances. Every single circuit in my home is monitored by an electrical monitoring system. With this system I can monitor all of the electrical usage in my house and as part of the monitoring process, what is rs485 cable I store this data in a MySQL database. One thing I also wanted to do was to monitor the filter pressure so I knew when to back flush our filter. Since I did not need a Pi for this, I choose a battery-operated, low-power Arduino wireless clone that would transmit the information back to an existing system that I already had in place around the house.

We also got our kitchen back which ended up being my workshop for the project. The design of RS485 is targeted towards it being tolerant and forgiving to noise and long cable runs with the twisted pair cable arrangement. Due to this and it being able to transmit data over long distances, the RS485 is used commonly as a protocol for POS, industrial and telecom. Termination resistors also reduce electrical noise sensitivity due to the lower impedance. However this contradicts the facts that an idle mark state is a logical one and the termination polarization puts B at a higher voltage in Profibus guidelines. I used the Sainsmart solid state relays (very inexpensive) in optically isolated mode where I have a separate power input powering the relays as opposed to using the 5v or 3.3v VCC from the Pi. Since I know several other people using the eTape with great results, I am going to leave everything about the eTape in my project and add to it the way I did the dual float setup. Initially, I had no intention of doing anything other than add water to the pool automatically, but as these things often go, the project grew with a mind of its own.

There was no other automation beyond those things. The capacitance is close to 12.5 pF/foot but there is a small impedance mismatch (100 ohms for Cat 5, 120 ohms for RS-485). These characteristics make RS-485 useful in industrial control systems and similar applications. On my Raspberry Pi, I utilize a Low Power Labs MightyHat which provides UPS power backup to the Pi, an LCD status screen and intelligent power control for the Pi. So I needed a way to monitor the power from my pump and figure out if it were running or not. I ended up using four of them in my project: one for the water level, one for the temperature of the water and two in the main system to monitor a combination of internal enclosure temperature, filter pressure and water usage. By using repeaters very large RS-485 networks can be formed. Let’s consider a simple example of an RS-485 network with one master device and two slave devices.