voice recording playback

8/2/2019 Voice Recording Playback

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c o n s t r u c t i o n

electronics for youseptember 2004

the microphone networkthrough capacitors.

R e c o r d i n g s i g -nal rom the externalsource can also be eddirectly into the chipusing Ana_In (pin 20),but the connection be-tween Ana_In (pin 20)and Ana_out (pin 21)is still required orplayback. An internalanti-aliasing ilter au-tomatically adjusts itsresponse according tothe sampling requencyselected. Then the sig-nal is processed intothe memory arraythrough a combinationo the sample-and-holdcircuit and analogueread/write circuit. Theincoming voice signalsare sampled and theinstantaneous voltagesamples are stored inthe non-volatile lashmemory cells in 8-bitbinary encoded ormat.

During playback,the stored signals areretrieved rom thememory, smoothedto orm a continuoussignal, low-pass il-tered and then ampli-ed. The signal level atthe speaker terminalsSP+ and SP- (pins 14and 15, respectively) isat about 12mW powerinto 16-ohm impedance. The output rompin 14 (SP+) is urther amplied by thelow-power amplier using LM386 (IC2) asshown in the gure. The recorded messageis reproduced into speaker LS1.

An internal oscillator provides sam-pling clock to the APR9600. The re-quency o the oscillator and sampling ratedepend on the value o resistor R12[R12(A)+R12(B)] connected across OSCR(pin 7) o the chip and the ground.

Table II shows the sampling requen-cies corresponding to dierent resistorvalues, as well as the resulting input band-width and duration o recording. Highersampling rates improve the voice qualitybut they also increase the bandwidth re-quirement and thus reduce the duration.Lower sampling rates use ewer memory

Fig. 2: Random-access mode confguration

cells and eectively increase the record-ing/playback duration o the device. TheRC network (comprising resistor R9 andcapacitor C2 connected) at pin 19 sets theAGC attack time. (The attack time is de-ned as the delay present beore the AGCcircuit begins to adjust gain.)

Message management. The APR9600chip supports the ollowing messagemodes:

1. Random-access mode with 2, 4or 8 messages within the total recordingtime.

2. Tape mode with two options: autorewind and normal opera-tion.

The modes are denedby pins 24 (MSEL1), 25(MSEL2) and 9 (/M8_Op-tion) as shown in Table I,and cannot be mixed.

An important eatureo the APR9600 chip is in-dication o changes in thedevice status through beepssuperimposed on the device

tabLe iirfnc roc Vlu nd Copondng

smplng Fqunc

rf roc smplng inpu Duon

fquncy ndwdh

84k 4.2 kHz 2.1 kHz 60 sec

38k 6.4 kHz 3.2 kHz 40 sec

24k 8.0 kHz 4.0 kHz 32 sec

Note.Rosc table above is for reference only, different lots of ICs will havesomewhat different Rosc value performance


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electronics for you september 2004

output; or example, the start o recordingis indicated by a beep, so the person cannow start speaking into the microphone.This eature is enabled by makingpin 11(BE) high.

General functional description.On power up, pin 23 (CE) is pulled

low through resistor R7 to enable thedevice or operation. Toggling this pinby switch S9 also resets several messagemanagement eatures. Pin 27 (RE) ispulled low to enable recording andit is pulled high or playback. To startrecording/playback, switch the appropri-ate trigger pin as described later. Glow-ing o LED1 indicates that the device isbusy and no commands can be cur-rently accepted. The LED is driven by pnptransistor T1, which is connected to pin 10

(Busy) o the chip. LED2 indicates record-ing in each individual memory segment.It is driven by pin 22 (strobe) throughtransistor T2.

rdom-cce mode

As mentioned earlier, the random-accessmode supports 2, 4 or 8 messages o xeddurations. It allows easy indexing o mes-sages as they can be recorded or playedrandomly. The length o each message isthe total recording length available (as de-ned by the selected sampling rate) dividedby the total number o memory segments/tracks enabled (as per Table I).

Recording of sound. The circuit orrecording/playback o eight xed-durationmessages in random-access mode is shown

Fig. 3: Circuit or recording/playback in tape mode with auto-rewind option

in Fig. 2. Pins 9 (M8_Op-tion), 24 (MSEL1) and25 (MSEL2) are pulledhigh through resistorsR1, R6 and R5, respec-tively. When switch S10is closed, record pin 27(RE) goes low to enablerecording o the messagerom the microphone.The maximum length othe eight sound tracks is7.5 seconds each.

Now to start record-ing the irst message,press switch S1 and holdit in this position. A beepsound is heard and LED2blinks. You can nowspeak into the condensermic. The recording willterminate i switch S1 isreleased or i the record-ing time exceeds 7.5seconds. Similarly, pressswitches S2 through S8to record other soundtracks. For recording otwo or our sound trackso ixed duration, thestatus o pins 9, 24 and25 is as per Table I.

Playback of sound

tracks. Open switchS10 to make pin 27high while keeping otherswitches in the samepositions as in record-ing. Toggling switchesS1 through S8 causesplayback o particularsound tracks. Pressing

the same switch again or switch S9 termi-nates playback o the sound track. Pressingany other switch (S1 through S8) while asound track is being played causes a newsound track to be played. I the switch isheld pressed, the particular sound trackwill play continuously.

tpe mode

The tape mode operation is muchlike the conventional cassette taperecorder, but with auto-rewind and normaloperation options. In auto-rewind mode,the device automatically rewinds to thebeginning o the message immediately aterrecording or playing the message. In normalmode, it must be switched or rewind.

Sound recording in tape mode with


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electronics for youseptember 2004

Fig. 4: Circuit or recording/playback in tape mode with normal option

auto-rewind option. Fig. 3 shows the circuitor recording/playback in tape mode withauto-rewind option. In this conguration,pins 24 (MSEL1) and 25 (MSEL2) are con-nected to ground, whereas pin 9 is pulledhigh through resistor R1. Close switch S10to enable the recording o message. Pressswitch S9 to reset the sound track counter tozero. Now press switch S1 and hold it in thisposition. A beep sound is heard and LED2starts blinking. This means you can speak

into the mic. Recording will terminate whenswitch S1 is released or i the recording timeexceeds 60 seconds. Press switch S1 againand again to record second, third, ourthand other consecutive sound tracks. Eachsound track may have a dierent length butthe total length o all sound tracks cannotexceed 60 seconds. When LED3 lights upduring recording, it indicates the end omemory array.

Playback in tape mode with auto-

rewind option. Open switch S10 to pull Fig. 5: Combined actual-size, single-side PCB or circuits o Figs 2, 3 and 4

pin 27 high while keep-ing other switches in thesame positions as appli-cable during recording.Toggle switch S1 repeat-edly to play consecutivesound tracks. Press switchS9 to reset the sound trackcounter to zero. Duringplayback, LED3 indicatesthat all recorded messageshave been played.

Recording in tape

mode with normal op-

tion. Fig. 4 shows thecircuit or recorcding/playback in tape modewith normal option. Con-nect pins 24 (MSEL1), 25(MSEL2) and 9 (M8_op-tion) to ground. Closeswitch S10 to enable therecording o message.Press switch S9 to resetthe sound track counterto zero. The normal-moderecording is similar to therewind-mode recording,except that ater swichS1 is released, the soundcounter doesnt incrementitsel to the next soundtrack location. To recordthe irst sound track,press switch S1 and holdit in this position. A beepsounds and LED2 blinks.Now you can speak into


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electronics for you september 2004

Fig. 6: Component layout or the PCB

sage will be recorded at the location o therst message.

Playback in tape mode with normal

option. Open switch S10 to pull pin 27high while keeping other switches inthe same positions as during recordingoperation. First, press switch S9 to resetthe sound track counter to zero. Nowmomentarily press switch S1 to play therst sound track. Momentarily pressing oswitch S1 again and again will still playthe rst sound track. The sound trackcounter can be incremented to play thenext sound track by momentarily pressingswitch S13.

The combined actual-size, single-sidePCB or the circuits o Figs 2, 3 and 4 isshown in Fig. 5 and its component layoutin Fig. 6.

To obtain the conguration o Fig. 2,connect connector Con1 to Con2 usingburgstick connectors with ribbon cableor simply using jumper wires. Similarly,conguration o Fig. 3 or Fig. 4 can berealised by connecting Con1 to Con3 orCon4. Note that switch S1 is common orall congurations.

the microphone. To record the next mes-sage, release switch S1 and toggle switchS13. Now press switch S1 again and holdin this position. A beep sounds and LED2

blinks. This means you can speak intothe microphone to record the message. Incase you press switch S1 without togglingswitch S13 to record the message, the mes-

voice recording playback

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