Kangaroo pet - ーDrop Detector; Fail-Safe; 一 Rotor Detection; Frame Detection

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3.

circuit

description

(cont.)

Drop

Detector

The

pump

monitors

fluid

flow

by

optically

detecting

drops

failing

through

the

drip

chamber.

Two

IR

LEDs

are

driven

by

constant

current

source

Q11

and

connected

to

the

circuit

board

through

J3

pins

3

and

4.

A

photodiode

is

likewise

connected

to

J3

pins

1

and

2.

The

photodiode

is

protected

from

the

effects

of

visible

light

by

a

polysulfone

filter

integral

to

the

drip

chamber

yoke.

The

signal

from

the

photodiode

is

amplified,

differentiated,

passed

through

a

sixth

order

low-pass

filter,

amplified,

chopped

and

finally

squared

for

presentation

to

the

microprocessor.

The

signal

from

the

photodiode

is

processed

by

U5

and

the

surrounding

passive

networks.

The

output

of

this

processing

is

then

buffered

by U1

and

then

input

to

the

microprocessor.

Motor

The

pump

motor

is

connected

to

the

pump

circuit

board

by

connector

J2.

Power

to

the

motor

is

controlled

by

FET

Q6.

The

motor

is

also

braked

by

FET

Q5.

Q6

and

Q5

are

never

turned

on

simultaneously,

and

are

time

delayed

so

that

they

never

transition

simultaneously.

The

microprocessor

controls

the

motor

from

port

TCMP.

This

signal

is

buffered

by

U1

and

the

surrounding

RC

networks.

The

RC

networks cause

the

dynamic

brake

O5

to

be

released

before

applying

power

through

Q6;

conversely,

power

to

the

motor

through

Q6

is

always

removed

before

applying

dynamic

brake

Q5.

Fail-Safe

In

the

unlikely

event

that

the

motor

should

continuously

run

and

not

turn

off,

a

fail-safe

circuit

will

crowbar

the

power

supply

to

ground

and

blow

fuse

Fi.

Constant

current

regulator

Q3

gets

its

power

from

the

motor

circuit;

as

the

motor

runs,

Q3

charges

capacitor

C3.

When

the

voltage

at

the

anode

of

Q2

exceeds

the

voltage

on

the

gate

(set

by

divider

R1

and

R2),

Q2

turns

on,

raising

the

voltage

at

the

gate

of

Q1.

When

the

gate

of

Q1

rises

above

ground,

O1

turns

on

and

allows

current

from

the

battery

to

pass

directly

through

it

to

ground,

blowing

F1.

The

fail-safe

circuit

takes

approximately

13

seconds

to

trip.

Rotor

Detection

.

The

microprocessor

monitors

the

rotation

of

the

DC

motor

by

counting

pulses

generated

by

the

interaction

of

3

magnets

on

the

pump

rotor

with

Hall-effect

switch

S1.

The

microprocessor

receives

the

signal

from

S1

on

port

PD5.

Debouncing

of

this

switch

occurs

in

software.

Frame

Detection

The

microprocessor

detects

the

presence

of

the

backpack

frame

on

port

PD3,

using

Hall-

effect

switch

S2.

A

magnet

in

the

frame

will

close S2

when

the

pump

is

fully

inserted

into

its

pocket

in

the

frame.

Pump

Set

Detection

The

microprocessor

detects

the

presence

of

a

pump

set

on

port

PD7,

using

a

Hall-effect

switch

connected

to

the

pump

circuit

board

through

J1

pins

4,

5

and

6.

The

SIPS

magnet

on

the

pump

set

activates

the

switch

when

the

pump

set

is

properly

inserted

into

the

loading

arm

and

the

loading

arm

is

then

closed.

Audio

Alarm

Audible

alarms

are

generated

using

a

piezoelectric

element

connected

to

the

pump

circuit

board

through

connector

J4.

The

TTL-level

oscillation

generated

by

the

microprocessor

at

port

PC3

is

boosted

by

U14

and U15

to a

20

VDC

level.

12