Max485 Chip RS-485 Module TTL to RS-485 Module Raspberry Pi Pack of 5
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I'm not sure I understand your question. If you're looking for code examples, look up'max485 Arduino' on GitHub.
You can use more than two, but the most practical answer is that because these items are so inexpensive, shipping only makes sense when sold in bulk.
Selected User Reviews For Max485 Chip RS-485 Module TTL to RS-485 Module Raspberry Pi Pack of 5
First and foremost, I have not yet thoroughly tested all five of my ideas. br>br>I bought these to connect to a Raspberry Pi and use with the RS-232 protocol. My HVAC unit has a 485 bus. It wasn't quite as 'easy' as I had hoped. br>I'm thinking of doing something similar with an arduino (I believe I have one somewhere in my desk drawer). ) would probably be a little easier, but I haven't found an existing software stack for the HVAC system for an arduino, and since this is my first time working with RS485, I decided to stick with the'standard' bits. If you want to do what I did with a Raspberry Pi, there are a few things to keep in mind. br>br>I found some wiring diagrams on the internet that were helpful. a tad bit perplexing The DI and DO lines were connected to the raspberry pi UART TX and RX (GPIO 14 / 15), while the DE and RE lines were connected to GPIO pins (23/34 or bonded on GPIO18). br>br>First and foremost, let's discuss the UART. You must disable the serial terminal (defined as a linux kernel param in /boot/cmdline. txt). The 'raspi-' package in Raspbian is a must-have. This requires the use of the config' tool. BUT: Make sure that /boot/config is correct. txt contains the line 'uart_enable=1', which tells the /dev/ttyAMA0 driver to pick up the UART and publish the device. br>br>Once you've got your kernel parameters and config set up correctly, you'll probably try to connect your device to the 485 bus. If this bus is your HVAC system, you should work on it on a day that is not too hot or too cold. because. br>br>When a minimal raspbian install boots up, the GPIO pins bound to DE and RE are both HIGH, putting the 485 device into transmit mode and effectively interrupting the existing traffic on the bus. In the case of a Carrier/Bryant/Infinity HVAC system, this results in a 'bus communication error,' which causes the entire HVAC system to stop working until you remove your device from the bus. It was a good time. If all you want to do is read the bus traffic, just ground the DE/RE pins. br>We shouldn't be using GPIOs to trigger this if we want to write to it in a controlled manner. There was very little documentation on this that I could find, but what I did find stated that I should connect the DE/RE to the TX pin of my UART and use a latch-on circuit. When the TX pins go high, use a type circuit (a 555 timer would be ideal) to drive the DE/RE pins high, holding them there just long enough for the bit to transmit before resetting.
Instead, purchase a genuine RS485 integrated circuit from a reputable supplier. Junk. Rather than this cheap knockoff junk, purchase an RS485 chip from a reputable electronics distributor. I spent hours trying to figure out why my VFD wasn't receiving data, but it turns out that these things don't work in any electrically-powered environment. The point of differential signaling is defeated in a noisy environment. br>br>I double-checked my A- grades. B differential voltage signals from the VFD were crystal clear on my oscilloscope, but these modules would produce random noise spikes on RO; Because of common mode noise that should have been rejected, this is most likely the case. br>br>I replaced these with a genuine SP485 IC from Digikey, and everything now works as it should.
They do a fantastic job. (Caveat: I've only ever run DMX with them for about 100 feet, nowhere near the 1300 feet (400 meters) that DMX512 allows. ) br>br>Would be a five-star rating if the layout was more logical: Instead of 4 and 4, use a 6 pin header with VCC, GND, DI, DO, RE, and TE at the same end, and a 3 pin header with A, B, and GND at the other end. br>br>Comes equipped with a terminatorbr>- You can either desolder or shatter the chip resister if you don't need it.
- It's a bit big for what it does. br>br>Note: If you're looking for a unique way to express yourself, try using the words "creative Some claim that this is a 5V only board, making it incompatible with the Pi, which runs on 3. 3V GPIO. I've been able to get them to work at both 3 and 4. 3V and 5V (the only site that mentions using this board with a Pi for DMX uses 3V). 3V). This board has three inputs (two enable and one data in) with low enough thresholds for a swing of three. 3V logic, as well as a data output that doesn't appear to be capable of harming a Pi serial input. If you're concerned about this, place a simple voltage divider on the board's DO.
It did exactly what I needed it to do, which was to connect two Arduino boards via long serial lines for half-duplex communication. Connect the DE/RE pins to an arduino digitial out, and the TX/RX to the arduino uart. Drive a high/low after a delay, allowing the bootloader to function normally, and allowing you to select TX/RX from within your program. If the VCC/GND pins were not on the same header as the A/B bus, the layout would be a little more convenient.
On a Raspberry Pi, this will not work. The UART (and GPIOs) on the Raspberry Pi do not support 5V. This circuit is powered by a 5V battery. It should not be sold as a Raspberry Pi compatible device because it was designed for an Arduino.
Two out of the five modules were delivered in a timely manner.
This is a joke!.
It was necessary to connect an Arduino to. These things worked out quite well. To simulate a sensor, I had to use an Arduino and then an RS-232 cable. 485 to a master, who converts it to a tcp packet For my proof-of-concept, it was ideal.
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