![]() I did a couple of experiments around deriving from the RS485 class of pySerial and moving the time critical code (disabling the transmitter after the transmit) into C code failed. ![]() Thus, the receiver of the master was still disabled. The response of the device would already start when the transmitter of the master was still enabled. The long hold time of about 18ms of the DE (transmitter enabled, RTS line) became a problem. In this article, Iâll walk you through how I created my own RS485 HAT for a Raspberry Pi based on the Modbus communication protocol. Most of them came as open source hardware, so I was able to compare the particular schematics with the related data sheets and application notes for the central RS485 transceiver. With some Googling, I found a few off-the-shelf Modbus RPi HATs on eBay and Amazon. Recently, I found a lot of interesting, cheap Modbus-connected devices (Remote IO, PT100/PT1000 converters, etc.) on eBay and I became curious about working on a more advanced, configurable Modbus master again. However, I soon after discovered ESP8266 modules and I switched more or less completely to connecting homegrown devices via Wi-Fi. I built a thermometer and alarm system for the freezer and the fridge in the basement with a very simple Arduino-based Modbus master with very limited hardware and only hardcoded mapping of client registers. So far, Iâve connected these devices via Meterbus. Iâve been playing around with the Modbus communication protocol, considering it as an alternative communication system for my homegrown smarthome devices.
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