In what follows we describe the internal structure of each board. See 2.12 for a global description of the electronic controller.
- Main board (see Fig. C.6). The ComPic is connected to the TrapPics by two ports. Port E controls the flow of data and the Port F is a custom parallel bus devoted to data transfer. Similarly, Port A is used to control the communication between the ComPic and the USB transceiver (DLP-USB245M-G) and the Port D is an 8-bit parallel bus used to write and read data. The 3 PICs use the port C to communicate with other chips of the electronic board via an SPI module. By using the SPI, the ComPic communicates with the MotorPic. The TrapPics communicate with the AD and DA converters. The Chip Select (CS) pin controls the communication. Finally, the Port B is used to burn and debug the firmware in the PICs with an In-Circuit Debugger (ICD).
Main board schematics.
- Preamp board (see Fig. C.7a). The current provided by the 4 electrodes of the PSD is converted into a voltage by using operational amplifiers that work as current-to-voltage converters. The current from the IRIS detector is also converted into voltage. The converted voltages from the PSD are combined to obtain the desired signal: subtraction gives the deflections (DX and DY) and addition gives the total power (SUM or PSDSUM). There are 2 Preamp boards per trap: one for position PSD and one for the force PSD.
- ADC board (see Fig. C.7b). The signals that come from the Preamp board are stabilized and filtered by using voltage followers and RC analog filters (1 kHz bandwidth) before their enter the AD converter chip (Allegro MAX1168). It is a 16-bit 8-channel (although 7 channels are used only) converter that communicates with the TrapPic located at the main board via SPI bus.
(a) Preamp board. (b) ADC board. The bottom right channel of the ADC is not used.
- Motor board (see Fig. C.8). This board has a complex combination of analog driving of motors (H-bridges), digital control of motor limits using logical gates (TTL technology) and digital processing of data (MotorPic and counters). The 3 motors are driven independently by 3 H-bridges located in two chips (one chip is shared by the and motors). The H-bridges provide the power to the motors in the correct polarity in order to make them rotate in one direction or the other. The direction and the speed of the motors is controlled by the MotorPic by means of Ports A and G respectively. The output of Port G is a Pulse Width Modulation signal that drives the motors. Between the motors and the MotorPic there are logical circuits (TTL protection made with AND, NOR and NOT gates) that prevent the breakage of the motors by disconnecting the H-bridge when the limit switches are exceeded. The MotorPic also reads the status of the limit switches in Port F. The shaft encoders of the motors send their pulses to three 24-bit counters, one for each motor. The MotorPic reads and controls the data from the counters by means of the Ports E and D respectively. Port C is used to power the blue LED that illuminates the optical path and to communicate with the ComPic in the main board. Finally, Port B is used by the ICD to burn the firmware as in the PICs of the main board.
- DAC board (see Fig. C.9). This board is shared by the two traps. There are two independent digital to analog converters (Texas Inst DAC8534IP) that communicate with the TrapPics via SPI. The analog output voltage from the DAC is send to 4 op-amps that amplify the voltage to a range between 0-150 V. The voltage is applied to the piezos of the wigglers that reposition the two optical traps in the and direction.