Last week’s project demos

• Servo control with photoresistor and enable/disable buttons

• Demo in class tonight – don’t start on the next project until I’ve seen this one!

More circuit design

Seven segment display

The Seven-segment Display

• Nothing more that 8 LEDs in a single package– Each LED can be turned on/off

independent of all others

The Seven-segment Display• Like individual LEDs, each has a cathode and an

anode leg

• The anode of each LED is routed to its own pin on the package

• All cathodes are connected together and routed to two pins on the package (choose one of the other)

Schematic

• The schematic shows the part as seven separate LEDs (as expected)

Usage

• Use them as seven separate LEDs• That is, for whatever you would

normally use an LED for

Typical circuit schematic and layout

• See chapter 7 for example code– It’s just a bunch of OUTH and PAUSE statements

Memory usage• So far we have been writing to individual pins on the Basic

Stamp module• For the seven segment display it would be convenient to write to

multiple pins at one time• The I/O pins are memory mapped to various PBASIC Word type

instructions – INS, OUTS– These are broken down further to Byte type instructions

• INL, INH, OUTL, OUTH (Low byte, High byte)• These are broken down further to Nibble type instructions

– INA, INB, INC, IND, OUTA, OUTB, OUTC, OUTD– These are broken down further to Bit type instructions

» IN0 – IN15, OUT0 – OUT15• Utilizing these instructions will set the direction of the pin

accordingly

Memory usage• Another instruction called DIRS (and all size

variations) is available to set the directions of the I/O pins

• We saw this earlier when we needed to “disconnect” an output pin– Set the bits to 0 for input direction– Set the bits to 1 for output direction– Default power up is input

• This is useful when setting up to do I/O without actually doing the I/O operation

Homework• By changing the value of the capacitor the time decay can be altered

– Book labs had you do this• For this assignment

– Build RC circuits using both 0.1uF and 0.01uF capacitors to create 2 timers (select one resistor value)

– Include a button to select one of the two timer s• Include debug statements to indicate timer decay

– Use the bidirectional LED to indicate which timer is selected• Green – fast (short time decay)• Red – slow (long time decay)

– Include a 7-segment display in your design in some creative way

Deliverables

• Due next week– A functional description of the system– A state-machine diagram depicting the

operation of the system– Source code– A schematic diagram of the circuit– A working demonstration on the Basic

Stamp development board (in class)