HIGH TECH

CHIPS, INC.

04/30/00

2

2.0 Functional Description.

We will use schematics above to describe HTC750 operation. At power up HTC750 plays melody set

by dip-switch. After finishing melody it goes into sleep mode and drives all outputs to GND. In

prototypes we build using above schematics current consumption was less then 10uA. This current is

negligible enough to leave circuit constantly powered on. When device is in Sleep mode only way of

waking up the circuit is to recycle power. This is done using S1 pushbutton. Note that we are using

pushbutton with normal closed contacts. When this pushbutton is activated power to HTC750 is cut

down and when this pushbutton is released then part will play the melody. One can use pushbutton

with normal open contacts but it could result partial reproduction of melody.

Note the way CNTL output is used to save energy during Sleep mode. Energy saving is achieved by

cutting power to R1 and R2 resistors when part enters into Sleep mode and preventing battery

discharge through those resistors when associated dip-switch is on. T1 and T2 form simple current

amplifier to drive 8-ohm speaker. Almost any small signal transistor could be used in this amplifier.

Note that this amplifier will introduce additional distortions to amplified signal, because transistors are

not biased. This is done intentionally to simplify amplifier circuit and add one distinct character. This

amplifier does not use any current when its input is driven low. Any other amplifier circuit could be

used as long as care is taken to shut down the amplifier with CNTL output of HTC750 to save buttery.

This could be done by external relay. Quality of sound could be further enhanced if low pass filter is

added to output of HTC750. Please see Application note for HTC750.

Pin out description.

Abbreviations used: O - output, I - input, P - power.

Pin

Name

I / O Description

Notes

1

VDD

P

Power

+2.5V to +5.5V

2

NU

I

Not Used

Tie it to GND or VDD.

3

NU

I

Not Used

Tie it to GND or VDD.

4

D1

I

Melody selection input.

Tie it to GND or VDD.

5

D0

I

Melody selection input.

Tie it to GND or VDD.

6

CNTL

O

Control output

This output is driven high when part plays

melody. Can deliver up to 25mA current.

7

MOUT

O

Melody output

Signal on this output is square wave.

8

GND

P

Ground

Connect to ground.

3.0 Melody selection with D[0:1]

D1

D0

MELODY

GND

GND

Number 1

GND

VDD

Number 2

VDD

GND

Number 3

VDD

GND

Number 4