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DIY time-lapse movie camera - system description -
Introduction:
The DRV8412 evaluation kit (DRV8412-C2-KIT) includes everything needed to spin a single stepper motor out of the box. It consists of the DRV8412 motor driver, a C2000 Piccolo F28035 MCU controlCARD, example software, code development environment, and the motor. This highly integrated, robust motor control and driver solution allows developing for stepper motors. The KIT has been extended by a little PCB that layouts buttons and the digital output to trigger the camera capture remotely.
System concept:
The DRV8412-C2-KIT offers a DIMM module connector at which the Piccolo ISO controlCard can be plugged into. The software project “Stepper” provided as part of the controlSUITE package programs the KIT to spin the stepper motor right away. Reviewing the code will show how to change speed and direction. Even, drive strength can be adjusted. Five buttons are routed to the GPIO input pins 6 to 9 and 12. These buttons are read frequently to allow selecting modes and to kick off the motor’s move. The GPIO input pins 4 to 5 identifies full stop position approaching the end of the slider rail. GPIO output 15 connects the remote capture trigger of the camera. In order to ensure isolation of both the systems (DRV8412-C2-KIT and Digital Still Camera) one optocoupler has been incorporated.
System assembly:
The DRV8412-C2-KIT provides one ISO controlCard that can be plugged into the KIT easily. The user’s guide describes the motor’s cable set to be connected to the KIT. In addition, one 24V power supply is provided.
ISO control card
DRV8412-C2-KIT
The slider rail including the slider can be ordered as a set. However, tooth belt, wheels and the motor need to be mounted. To avoid the slider to exceed the end of the rail position two full stop switches ensure this not to happen. Additionally, a mounting plate helps to attach the housing of the electronic system.
In order to connect digital inputs and the output I took an existing PCB which I designed earlier for different purposes. However, including some blue wiring the functionality could be enabled. The wires for the switches to identify End Of Rail position and the optocoupler to trigger the cameras capture have been added. It fits quite well for the first prototype.
One ribbon cable interconnects the extension PCB with the DRV8412-C2-KIT. The ribbon cable has been soldered at the backside of the DIMM module’s socket. The KIT’s schematic and the KIT’s PCB layout help to find the GPIO pin out.
System functionality:
The following system functionality has been incorporated as of today. Because no display and keyboard is built in system control is limited to major functionality. In total five buttons allow control as follows.
1. Button #1 instructs the motor to move forward at slowest speed (default speed). As the button will be hit during motor’s move speed can be increased in eight steps. Exceeding step eight will result in turning back in motor’s default speed.
2. Button #2 instructs the motor to move backward at slowest speed (default speed). As the button will be hit during motor’s move speed can be increased in eight steps. Exceeding step eight will result in turning back in motor’s default speed.
3. Button #3 will immediately stop the motor and will reset any other mode set. 4. Button #4 configures the system for Stop Motion mode. In steps of eight different times
the user can select the capture time required for scene to capture. 5. Button #5 will enable Stop Motion mode. In this mode the system will start to move for
half a centimeter before it stops. It will wait and trigger the cameras capture remotely. As the capture is complete the system will go on and move for another half a centimeter. In turn, it will stop again for additional remote camera capture. This sequence will proceed until the end of the slider’s rail. With help of button #3 the mode can be cancelled at any time.
Future work:
1. In order to add advanced HMI capability I’m thinking of taking the SimpleLink CC3200 EVM. It provides Wi-Fi router support along with webserver functionality fully integrated. Hence, by little html programming every smartphone or PC user could configure the system browsing to the webserver’s page. No need for integrating LCD displays or keyboards will be required. The EVM module is small fitting in the housing. It can be interconnected with the DRV8412-C2-KIT using UART, SPI, I2C or even GPIOs.
2. The system can be extended introducing a second axis. It will allow the camera to rotate while the slider is on move. This will open up a new level in time lapse recordings. A smaller form factor solution is provided by the MSP430/ DRV8711 team. It is capable of driving smaller stepper motors and fits quite well on the slider itself. Incorporating the MSP430 Launchpad “MSP-EXP430G2” and the motor driver add-on board “BOOST-DRV8711 Stepper Motor Booster Pack” will make the camera to rotate.
References:
1. Microstepping.pdf 2. DRV8412EVM_RevG-Schematic.pdf 3. DRV8412-C2-KIT_HowToRunGuide.pdf 4. F28035_ISOcontrolCARD-PinOutTable.pdf 5. DRV8412EVM_RevG-BottomCopper.pdf 6. DRV8412EVM_RevG-TopCopper.pdf 7. DRV8412EVM_RevG-Schematic.pdf 8. MotorControl_MSP430_DRV8711_slvu967.pdf 9. MSP430BoostMotorControlUsersGuide_slvu967.pdf