Wiring
Before you start, you should be aware that such an intervention will invalidate any warranty. Without sufficient knowledge of electronics, there is a high risk of irreparable damage to the camera!
All emulators use the coil signals to generate the control signals for the camera, which can be easily tapped into at the test points of the shutter cable. Only for the power supply voltage for some models, you need to solder directly on the EOS mainboard, but that is quite simple. (Unfortunately, the power supply of the coils can be used to power the Arduino only in the EOS M models because it is not permanent or, as with the 700D, too late.)
The Arduino outputs are isolated from the camera electronics by diodes to prevent damage to the camera electronics if the operating voltage of the Arduino is higher than 3.3V. Thus, for example, a test operation with a 5V Arduino via USB is easily possible.
The wiring differs significantly for the various camera types, with their shutters sometimes having only one holding magnet ('coil') (1100D, M), while others have two. The single and double-digit models (6D, 50D, etc.) also have a separate motor with additional control signals for the mirror.
Connection scheme for the 550D and 600D, for additional models see below.
The description of the functions of the individual signal lines can be found in the control program.
The resistor 'Rs' is optional and serves to protect the mainboard against short circuits. It must not be chosen too high, otherwise the Arduino will have start-up problems. Values around 20 Ω seem well suited.
If a Bluetooth module is used, it should be omitted.