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I read some articles about the AT commands but I am still unable to understand something. As the article says "AT commands are instructions used to control a modem." I used a while ago an Bluetooth module(HC-05) to control a RC car and I saw that the module recognise AT commands. I could control the car using only UART communication and at that moment I just ignored the AT commands. So, why does the Bluetooth uses AT commands ?

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    \$\begingroup\$ Some quasi-modern devices use AT commands because they historically fit into roles or patterns of designer/user thinking dating back to smart wireline telephone modems that used them. Beyond that the question is too broad and off topic. \$\endgroup\$ – Chris Stratton Dec 12 '18 at 15:11
  • \$\begingroup\$ "AT commands" is a somewhat standard control protocol built mostly on top of serial interfaces. It is an ASCII protocol and can be used to enter commands "by hand" through a serial terminal of some sort. Other than that the reasons are mostly historical. \$\endgroup\$ – Eugene Sh. Dec 12 '18 at 15:17
  • \$\begingroup\$ @ChrisStratton is referring to 'smart modems used with telephones', not necessarily modems used with smartphones (indicating that this is ancient command set). So yes, there's much history, and inertia with the use of AT commands. There is however, no reason one must use them. Once learned, they are human readable. Other than that, no benefit that I'm aware of. \$\endgroup\$ – Chris Knudsen Dec 12 '18 at 15:17
  • \$\begingroup\$ Semi-standardization would be a benefit. For example, the Linux chat daemon can talk them; even non-standard vendor extensions because they have the same form regardless of the details. A custom scheme could need new software, not just new data. \$\endgroup\$ – Chris Stratton Dec 12 '18 at 15:20
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    \$\begingroup\$ It's important to note that Bluetooth itself doesn't use AT commands. It just happens that the Bluetooth device is configured as a serial device that responds to AT commands. \$\endgroup\$ – selectstriker2 Dec 12 '18 at 16:17
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As far as I know you can configure the HC-05 module with AT commands. Sometimes you want to change the baud rate of the module, the role (master - AT+ROLE=1 /slave - AT+ROLE=1), to get module Bluetooth address(AT+ADDR?),or to reset the configuration (AT+ORGL). Take a look here to see how to enter in AT mode and how AT commands look like: http://www.linotux.ch/arduino/HC-0305_serial_module_AT_commamd_set_201104_revised.pdf

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