We decided to use Teensy micro controller. The electrical system had 3 main sub assemblies
1. Analog input from tape sensing and communication to Teensy
2. PWM control of DC motors using Teensy and motor drivers
3. Control of stepper motor using Teensy and stepper motor driver
A maximum of 3.3 V is supplied to the tape sensing sensor. The resistor to the diodes were chosen to ensure that the diode receives a maximum of less than 40 mA as mentioned in the data sheets. The maximum voltage recorded across the transistor output and ground will be less than 3.3V and hence will be compatible with the teensy system. The schematic can be found in the final report.
Motors were chosen such that the maximum torque provided by the motors is greater than the static friction resistance based torque the system will choose. Further, during the selection of motors, we also tried to ensure that the motor provides torque greater than the required torque at the desired speed at 12V. For PWM control of motors, a 12 V constant voltage is supplied to the motors using batteries connected in series and a linear voltage regulator. L 293 driver was chosen to drive the motors. Compatability between Teensy and L293 was checked (VIH,VOH, VIL, VOL, IOH, IOL considerations); the detailed workings can be found in the final report.
DRV 8825 was chosen to drive the stepper motor. We did not look into the torque considerations for the stepper motor since the amount of torque required is very small and intuitively we strongly believed analytical analysis is not required. Compatability between DRV 8825 and Teensy was checked. The detailed workings can be found in the final report