Communication & interfaces $[9]$

The litter box to be designed will make use of a UART to Wi$-$Fi converter to allow it to be

integrated into an IoT environment. The litter box transmits a $10-$byte packet via Wi$-$Fi every

$100$ ms containing its current status, allowing for near$-$live monitoring of the device. Due to

its low cost, you select an ESP$-01$ Wi$-$Fi to UART module. The UART protocol to be

implemented is $8$N$1$ with a baud rate of $19200$ bps$.$

Question $2\mathrm{.}1[5]$

$2\mathrm{.}1\mathrm{.}1.$You transmit an AT command to the ESP$-01$ module and receive the following

response:

Figure $2.$ Received Data Bits

Decode the response and provide the received ASCII characters. $[1]$

Text

$2\mathrm{.}1\mathrm{.}2.$ What should the value of the SPBRGHx:SPBRGx register be if the BRGH bit is set to

$1$ and the desired EUSART mode is $8-$bit asynchronous at $19200$ bps$?[1]$

$4$

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lOMoARcPSD$|13634000$

Decimal

$2\mathrm{.}1\mathrm{.}3.$What is the percentage error in the true baud rate of the device if the

SPBRGHx:SPBRGx registers are loaded with the value calculated above? $[1]$

Decimal

$2\mathrm{.}1\mathrm{.}4.$What alternative standard baud rate can be used for the same EUSART configuration

to provide the lowest error? $[1]$

Decimal

$2\mathrm{.}1\mathrm{.}5.$Using the baud rate of question $2\mathrm{.}1\mathrm{.}4,$ how long does it take to transmit a single

packet? $[1]$

Decimal

Question $2\mathrm{.}2[4]$

The litter box should be capable of storing a log of its cleaning activity for a month$$s period.

A healthy cat visits a litter box between three and five times a day. Each time the cat visits

the automated litter box, the current time and date should be stored in memory using an

$5$

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external EEPROM module. The date is stored in the format DDMMYY followed by the time

stored as HHMMSS$.$ Assume that the date and time are stored in ASCII format.

Assume that only a single cat uses the litter box.

$2\mathrm{.}2\mathrm{.}1.$To ensure adequate memory is available, assume that a cat will not visit the litter box

more than $5$ times a day. How much memory, in bytes, is required to store the logs of

the visits for a $31-$day month? $[1]$

Decimal

$2\mathrm{.}2\mathrm{.}2.$How many $31-$day months$$ worth of logs can be stored in the $24$AA$256$UID external I$2$C

serial EEPROM? $[1]$

Decimal

You decide to cascade five the EEPROMs. The PIC$18$ records the current time and date of

an entry and writes the data to a $24$AA$256$UID connected to the PIC via I$2$C$.$ The

$24$AA$256$UID is addressed as the $5$th EEPROM module. The final byte to be written to the

device is $0$x$68$ and is to be stored in the highest writeable address of the device $($that is not

write protected$).$ Give the byte write sequence, which should be transmitted from the PIC$18$

via I$2$C to store the required bit in EEPROM. Give the bytes in order starting at the control

byte.

$2\mathrm{.}2\mathrm{.}3.$First byte $[0\mathrm{.}5]$

$2\mathrm{.}2\mathrm{.}4.$Second byte $[0\mathrm{.}5]$

$2\mathrm{.}2\mathrm{.}5.$Third byte $[0\mathrm{.}5]$

$2\mathrm{.}2\mathrm{.}6.$Fourth byte $[0\mathrm{.}5]$

Binary

$6$General system description

Cat boxes, also known as litter boxes, are an infamous part of a cat owner's life. Although

these boxes provide a facility within which a cat can excrete its metabolic waste, they need

to be cleaned regularly to prevent the odor from spreading through a household. Cleaning

the litter box can be the biggest downside of owning a cat. The popularity of self$-$cleaning

litter boxes is rising. These litter boxes offer a plethora of features on top of removing

metabolic waste from the box and controlling odours.

You set out to design a litter box that cleans itself after being used. The presence of a cat is

detected using weight sensors$.$ The weight sensors are also used to monitor and track the

weight of a cat and can be used to distinguish between cats if more than one cat uses the

litter box. The weight of a cat and the number of times it uses the litter box in a day can be

used to detect abnormal behaviour and health problems.

Figure $1$ shows a self$-$cleaning litter box with a cylindric design. The cylindric design allows

the inside of the box to rotate slowly while the sand is sifted through a meshed surface. The

clean sand falls through the holes of the mesh while the clumped sand and other metabolic

waste rolls off into a waste container. The box then reverses direction to allow the clean

sand to shift back into position.