Kangaroo pet - Ambulatory Pump; Microprocessor; Power Supply; Power-On Circuit

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3.

circuit

description

(cont.)

ambulatory

pump

Microprocessor

Microprocessor

U4

controls

all

operations

of

the

pump

and

charging

base.

This

is

a

Motorola

MC68HC705C8

8-bit

processor

with

32

I/O

lines

available,

divided

into

four

groups

of

eight.

Port

A

drives

the

LED

display

segments;

Port

B

drives

the

LED

display

digit

driver.

FETs

and

the

keypad

rows,

and

also

reads

the

keypad

columns

and

SW1

outputs.

Ports

C

and

D

are

used

for

miscellaneous

non-bussed

1/0.

The

processor

is

driven

by

a 4

MHz

crystal

oscillator

that

clocks

the

internal

circuit

at

2

MHz,

resulting

in

a

1

us

minimum

instruction

execution

time.

The

processor

(in

the

configuration

used

here)

has

approximately

8

Kbytes

of

ROM

and

144

bytes

of

RAM

internally.

Power

Supply

The

pump

can

receive

power

from

its

internal

NiCd

batteries,

or

from

the

charger

base.

The

pump

contains

three

sub-C

NiCd

cells

with

a

capacity

of

1800

mAh.

The

battery

pack

connects

to

the

pump

circuit

board

via

connector

J6.

The

pump

may

also

operate

from

the

5

VDC

output

of

the

charging

base.

The

charging

currents,

5

VDC,

and

battery

are

prevented

from

backdriving

each

other

by

diodes

D1,

D10,

and

D16.

Power

from

the

acceptable

sources

is

fed

to

switching

voltage

booster

U2.

Voltage

levels

are

boosted

here

because

the

input

to

U2

is

unregulated

and

sometimes

significantly

less

than

5

VDC.

The

output

of

U2

in

turn

drives.

regulator

U7

which

produces

a

regulated

5

VDC.

The

output

of

U2

is

also

used

to

drive

the

pump

motor

connected

to

J2.

The

output

of

U7

drives

the

remaining

pump

circuit

not

driven

by

U2,

U13,

or

U6.

The

5

VDC

output

of

U7

is

also

fed

to

FET

Q7

to

create

a

switched

source

of

power.

U13

regulates

the

output

of

U7

down

to

4

VDC.

This

voltage

feeds voltage

inverter

U6;

outputs

of

U7

and

U6

power

the

drop

detection

circuit.

Power-On

Circuit

The

pump

circuit

may

be

activated

in

two

ways.

The

first

is

by

pressing

the

ON

key.

Activating

this

normally

open

switch

creates

a

negative

going

pulse

(dropping

to

ground

from

5

VDC)

that

is

connected

to

the

IRQ

line

of

the

microprocessor

and

to

U9

pin

2.

If

the

microprocessor

is

already

powered

when

this

occurs,

an

interrupt

is

generated

and

the

processor

turns

on

the

rest

of

the

pump

circuit

if

not

already

turned

on.

U9

and

Q4

and

the

resistors

and

capacitors

connected

to

them

form

a

latch

that

controls

FET

Q18.

Q18

lies

in

the

main

ground

path,

and

is

used

to

completely

remove

power

from

all

pump.

circuits

except

for

the

latch,

which

draws

negligible

power

because

U9

is

a

CMOS

IC.

A

negative

going

pulse

from

the

ON

key

will

turn

on

the

latch

circuit

and

©18

if

not

already

turned

on.

If

the

latch

and

Q18

turn

on,

power

will

be

generated

by

the

regulators

and

a

pulse

will

be

generated

to

the

RESET

input

of

the

microprocessor,

turning

it

on.

The

microprocessor

will

then

turn

on

the

rest

of

the

pump

circuit.

The

microprocessor

also

monitors

/O

line

PC1.

PC1

will

only be low

if

the

ON

key

has

been

pressed,

because

constant

current

regulator

Q10

keeps

C45

charged

even

when

the

latch

is

disabled.

If

the

pump

is

connected

to

an

active

charger

base

while

the

latch

is

disabled,

a

RESET

pulse

will

be

generated

as

above,

and

the

microprocessor

will

turn

on.

The

microprocessor

will

not

see

a

low

on

PC1

however,

so

the

microprocessor

will

turn

on

and

only

activate

timing

processes

in

the

software.

The

purpose

of

this

arrangement

is

to

enable

the

microprocessor

to

start.

quick

charging

the

10