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CAPE Wiki » cape1:subsystems:payload
 
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The following is work done by the first satellite team.

OBC

The OBC employed the Microchip PIC18LF6722 microcontroller. The extra general purpose input/output (GPIO) pins and the second USART port were major advantages for software development.

ADC

The ADCs on board were the Texas Instruments ADS7830. The ADCs are very sensitive to voltage changes on the inputs. For large voltage swings in short intervals, the best software fix is to take several readings from one channel and average them. Since we were interested in measuring the same voltage which was applied to Vin, our voltage reference could not be a function of our Vin. This would produce inaccurate results. Therefore, the ADCs were configured for a 2.5V internal voltage reference. This caused issues in cases where our measuring inputs would float above 2.5V.

For example, in order to measure the main power bus (MPB), the ADC was cofigured for 2.5V internal reference. Since the MPB would have values above 2.5V, we used a voltage divider circuit with 100K ohm resistors. This allowed a 3.3 voltage on the MPB to appear as a 1.65V reading on the ADC input. In software, however, we corrected this by multiplying the digital value by 2. Using this design tremendously reduces the accuracy of the ADC. CAPE1 accuracy for the voltage sensing was around +/- 10mV/bit.

adcinputs.jpg

The ADC communicates over I2C and can have up to 4 ICs connected to the same bus.

Design

The following ADC design was used on CAPE1.

adcschem.jpg

Notice the 8 analog input channels, main power bus (MPB), capacitor, resistors, ground, I2C data line, and I2C clock line.

Temperature Sensors

The temp sensors on board were the Dallas Semiconductor MAX6633.

The following is the temperature sensor schematic circuit used on CAPE1.

tempsensschem.jpg

Notice the connections to the main power bus (MPB), I2C clock, I2C data, and ground.

Current Sensors

The current sensors on board were from —

The following is the current sensor schematic circuit used on CAPE1.

currsens1.jpg

Notice the connections to the main power bus (MPB), solar panel connector (SP), analog to digital converter (ADC), diode, capacitor, resistor and ground.

RTC

The real-time clock on board was the Dallas Semiconductor DS3231.

The following is the real-time clock schematic circuit used on CAPE1.

rtcschem.jpg

Notice the power, I2C clock, I2C data, and ground.

WDT

The watch dog timer (WDT) on board was the Dallas Semiconductor MAX6814.

The following is the watch dog timer schematic circuit used on CAPE1.

wdtschem.jpg

Notice the power, reset line to FET, ground and input line.

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