Mini Audio Signal Generator - Elektor.pdf - Elektor - bombelek1410

amplifier of around d 50 W.

The crossover frequency of

the network may be varied

between 50 Hz and 160 Hz with

P 2 . The values of R 3 , P 2 , and

C 1 , are calculated on the

assumption that the subwoofer

amplifier to be connected to K 1

. If this figure is lower,

the value of C 1 will need to be

increased slightly.

It is advisable to open the

volume of the subwoofer ampli-

fier fully and adjust the sound

level with P 1 . This ensures that

the input of the subwoofer

amplifier cannot be overloaded

or damaged.

Make sure that the ground of

the loudspeaker signal line is

linked to the ground of the sub-

woofer amplifier. If phase rever-

sal is required, this is best done

by reversing the wires to the

subwoofer.

If notwithstanding the above

additional protection is desired

at the input of the subwoofer

amplifier, this is best effected by

‘overload protection ’ elsewhere

in this issue.

[984041]

electrical isolation for I 2 C bus

National Semiconductor

Application

When the SDA (Serial DAta)

lines on both the left and right

lines are 1, the circuit is quies-

cent and optoisolators IC 1 and

IC 2 are not actuated. When the

SDA line at the left becomes 0,

current flows through the LED

in IC 1 via R 2 . The SDA line at

the right is then pulled low via

D 2 and IC 1 . Optoisolator IC 2

does not transfer this 0 to the

left, because the polarity of the

LED in IC 2 is the wrong way

around for this level. This

arrangement prevents the circuit

holding itself in the 0 state for

ever.

As is seen, the circuit is

symmetrical. So, when the SDA

line at the right is 0, this is

transferred to the left.

The lower part of the dia-

gram, intended for the SCL (Ser-

ial CLock) line, is identical to

the upper part.

Resistors R 1 , R 4 , R 5 , and

R 8 , are the usual 3.3 k

the system, they may be omitted

here.

The current drawn by the

circuit is slightly larger than

usual since the pull-up resistors

are shunted by the LEDs in the

optoisolators and their series

resistors. Nevertheless, it

remains within the norms laid

down in the I 2 C specification.

[ 984024]

IC1

* siehe Text

* voir texte

see text

BAT85

* zie tekst

IC2 6

SDA

SDA'

BAT85

5V'

SCL

SCL'

BAT85

I C4 6

IC1...IC4 =

4 x 6N139

BAT85

IC3

pull-up

resistors that are obligatory in

each I 2 C line. If these resistors

are already present elsewhere in

984024-11

mini

audio signal generator

Design: T. Giesberts

A small audio test generator is

very useful for quickly tracing a

signal through an audio unit. Its

main purpose is speed rather

than refinement. A single sine-

wave signal of about 1 kHz is

normally all that is needed: dis-

tortion is not terribly important.

It is, however, important that the

unit does not draw too high a

current.

The generator described

meets these modest require-

ments. It uses standard compo-

nents, produces a signal of

899 Hz at an output level of

1 V r.m.s. and draws a current of

only 20 µA. In theory, the low

current drain would give a 9 V

battery a life of 25,000 hours.

The circuit is a traditional

Wien bridge oscillator based on

a Type TLC271 op amp. The fre-

quency determining bridge is

formed by C 1 , C 2 and R 1 –R 4 .

The two inputs of the op amp are

held at half the supply voltage

by dividers R 3 -R 4 and R 5 -R 6

respectively. Resistors R 5 and

R 6 also form part of the feed-

back loop. The amplification is

set to about

Elektor Electronics

7-8/98

has a standard input resistance

of 47 k

3 with P 1 .

Diodes D 1 and D 2 are peak

limiters. Since the limiting is

based on the non-linearity of the

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diodes, there is a certain amount

of distortion. At the nominal out-

put voltage of 1 V r.m.s., the dis-

tortion is about 10%. This is,

however, of no consequence in

fast tests. Nevertheless, if 10%

is considered too high, it may be

improved appreciably by linking

pin 8 of IC 1 to ground. This

increases the current drain of

the circuit to 640 µA, but the

distortion is down to 0.7%, pro-

vided the circuit is adjusted

properly. If a distortion meter or

similar is not available, simply

adjust the output to 1 V r.m.s.

Since the distortion of the

unit is not measured in hun-

dredths of a per cent, C 1 and C 2

may be ceramic types without

much detriment.

220k

1N4148

500k

BT1

330p

100

IC1

25V

100n

TLC271

R10

330p

[984033]

984033 - 11

ultra-low-power

5 V regulator

Design: T. Giesberts

The current drain of the regula-

tor is minute compared with that

of, say, a 78L05: at an input

voltage of 9 V and open-circuit

output, it is just under 50 µA.

The circuit consists of a

straightforward bandgap refer-

ence based on T 1 and IC 1 , fol-

lowed by an amplifier formed by

IC 2 and T 1 .

The reference voltage is

about 1.22 V, which is raised by

IC 2 to 5 V. The output voltage

can be set to exactly 5 V with

P 1 . The input voltage may lie

between 6.5 V and 30 V. The

maximum output current with

the present configuration and

component values as specified

is about 10 mA.

For optimum performance,

T 1a and T 1b need to be identi-

cal, which is why a dual transtor

Type MAT02 is used. Other

types that may be used are the

MAT01, SSM2210 or LM394.

In principle, two standard BC

transistors may be used, pro-

vided they are selected for iden-

tical threshold voltage.

Circuits IC 1 and IC 2 are pro-

grammable op amps Type OP22.

In the case of IC 2 this has the

benefit that the peak output cur-

rent can be set readily by altering

the supply current to the op amp

with R 9 . The level of the current

may be between 500 nA and

400 µA. Bear in mind that a

larger output current requires

6V5 ... 3 0V

IC1

470p

IC2

82k

OP22

547B

T1a

T1b

10mA

MAT02

390p

100n

63V

25k

* siehe Text

984034 - 11

I out = 1mA

= 9V

0V41

0V44

1V22

* voir texte

0V45

1V22

5V65

the use of a more highly rated

output transistor.

Filter R 6 -C 1 prevents any

spurious pulses reaching the

input of IC 2 . Capacitor C 2 im-

proves the stability of the regu-

lator, particularly with maximum

pulse loading.

Note that the circuit has a

high resistance, so that it is

advisable to house it in a

screened enclosure to prevent

undesired magnetic and electro-

magnetic interference being

Table 1

V in (V)

I g (µA)

V out (V)

V ripple (mV rms )

5.002

110

5.002

100

5.002

123

5.002

coupled to the circuit.

The regulator was tested with

a direct load current of 1 mA on

which was superimposed a

square-wave current of 10 mA.

The test results are summarized

in the table, in which I g repre-

sents the current drawn by the

circuit.

[984034]

Elektor Electronics

7-8/98

zie tekst

* see text

Mini Audio Signal Generator - Elektor.pdf

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