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| Turning a motor on that uses RS485 modbus communication |
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| ZeTeX:
Hello, I have a DC motor model m3g084-fa22-16, like in this video: The motor uses RJ-45 connector, with RS-485 communication protocol, to control the RPM and to start the motor on-off, from a control board. However, I need to find a way to turn the motor on/off without RPM control, and without the RS-485 communication from the board, or at least find the data used to turn the motor on. The reason for this is that the control board is not working, and it is replaced completely with a mechanical solution, not electronics, in a combi steamer. But replacing the motor to a simple asynchronous AC motor is quite expensive, and since the DC motor works, it might not be necessary. basically, make it so the motor works just by a switch, that turns it on and off. But there is no manual instruction for the motor on the web, and I'm not sure how it could be done. One way might be to "sniff" the data the control board sends to the motor with RS-485, and then send the data using a micro-controller for example. if so, would buying an RS485 to USB converter on eBay, and downloading software to show the data, connecting to other working control board and sniffing the data the control board sends via the protocol and then sending this data by an Arduino for example, would work? Thanks. |
| ZeTeX:
No ideas? Sent from my LG-H815 using Tapatalk |
| Ian.M:
I wouldn't gamble on a RS485 to USB converter getting the job done as you wont get anything useful in the PC terminal program if the bus uses an odd-ball baud rate or encoding/framing. Got a DSO, preferably with protocol decoding that includes async and sync serial formats? If so that will do nicely to 'sniff' the bus, and identify the encoding or framing being used over the RS-485 physical layer. If the encoding/framing is one the scope's decoder supports, you'll be able to identify the commands to send directly. If you don't have a protocol decoder post the best quality scope screenshots you can and ask for help working it out. If you don't have a scope, get a cheap Salae Logic 8 clone (to use with the open source Sigrok software) and a RS-485 transceiver breakout board to convert the bus to logic signals. You'll need the transceiver anyway for the Arduino. |
| ZeTeX:
--- Quote from: Ian.M on January 11, 2019, 12:25:11 pm --- I wouldn't gamble on a RS485 to USB converter getting the job done as you wont get anything useful in the PC terminal program if the bus uses an odd-ball baud rate or encoding/framing. Got a DSO, preferably with protocol decoding that includes async and sync serial formats? If so that will do nicely to 'sniff' the bus, and identify the encoding or framing being used over the RS-485 physical layer. If the encoding/framing is one the scope's decoder supports, you'll be able to identify the commands to send directly. If you don't have a protocol decoder post the best quality scope screenshots you can and ask for help working it out. If you don't have a scope, get a cheap Salae Logic 8 clone (to use with the open source Sigrok software) and a RS-485 transceiver breakout board to convert the bus to logic signals. You'll need the transceiver anyway for the Arduino. --- End quote --- I have a scope, Rigol DS1054. However, I noticed a slight issue. it turns out there is no standard pinout for RS485 RJ45. How can I know which 2 pins are +/-RX and +/- TX? |
| ajb:
Can you reverse engineer the PCB? There are tons of RS485 transceivers on the market, but mostly they're SO8 packages that will be somewhere near the connector. Note that there may be only one bidirectional pair, or there may be two separate pairs for transmit and receive. If there are separate fixed-direction pairs there will be two separate transceivers or a separate transmitter and receiver (in the latter case, they might be SOT6 packages instead of SO8). Otherwise, probe the various pin combinations and see if you can find valid idle voltages anywhere, and if that doesn't work, you're only option is to start poking it and see what happens. Ideally, though, you want to find a working system and monitor its bus transactions, that's hands down going to be the easiest way to figure out how to control the motor. |
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