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Communications Electrical Layout 

Transmitting:

Transmitter Schematic

The 555 timer generates the 40 kHz carrier frequency that is the basis for transmissions. 40 kHz was chosen to be compatible with the 40 kHz "silver box" that serves as the receiver on the ground station. The carrier signal is then coupled with the frequency modulated data signal from the CPU and sent through a ULN2003 darlington to boost current and drive the infra red LED.

Receiving:

The system receives a pulse from the ground station and transmitted through the IR LED and perceived by the IR detector (the silver box). This pulse signal is inputted in a Dual D Flip Flop 74LS74 that toggles between a high and a low Q_bar. This value is sent to the CPU where the switch is made between the sun sensor and thermal sensor. We had a problem with noise disrupting the signal and causing the flip flop to toggle at random so additional logic was added to suppress this phenomenon. The 555 timer which produces a 4.8 Hz signal, the logic gates, and the second flip flop on the chain all serve as noise suppression.

Receiver Schematic 

The Ground Station:

The ground station was designed and built in conjunction with the NOVA designs and consists of a IR detector, an IR emitter, and a button. Depressing the button toggles between a high and a low signal which are transmitted on the carrier signal and received and interpreted by the satellite to switch between the thermal and sun sensor and trigger the payload.

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