Audio Record/Playback Circuit using IC ISD1820

The post  explains the functioning of the  IC ISD1820 which is a single chip audio message record/playback chip featuring a 20 second audio recording and storing facility in its internal memory and playing it back through a small 8 ohm speaker whenever required.

Introduction

The IC ISD1820 is a device which features a single chip audio message recording and playback facility, and is able to retain the audio message in it infinitely even while the chip in the un-powered state.

The recording-playback and erase cycles can be implemented as many as 100,000 times without any form of degradation, that’s so huge and looks almost infinite in this regard too.

The maximum recording an playback time available from this chip is no longer than 20 seconds.

The technical features of this record/playback module IC ISD1820 can be studied below:

1) Can be operated with DC 2.4V to 5.5V

2) Includes an internal audio amplifier circuitry capable of handling a 8 ohm ½ watt speaker directly at its output.

3) Works with a standard electret MIC as the input audio or voice detector.

Pinout Functions:

Audio Record/Playback Circuit using IC ISD1820

Referring to the proposed 20 second message record/playback circuit diagram using the IC ISD1820:

1) Pin#1 can be seen as the REC (recording) input pinout, which accepts a positive signal for enabling the recording function, meaning this pinout must be connected to the Vcc or the positive line while recording an audio clip,

The REC pinout has the ability to take precedence over the other pinouts marked PLAYE/PLAYL in case it is pulled high while any of the other pinouts were functioning.

Meaning suppose if any of the PLAY button was pressed, and simultaneously REC was pressed, in such case the recording (REC) will be immediately initiated terminating the PLAY action.

The voice recording action can be stopped as soon the relevant button is switched OFF, and the REC pinout is rendered at LOW. In this position an internal EOM or end of message prompt is triggered internally, causing the PLAYBACK mode to get in the ready position. This also causes the chip to go into a power down condition or in the standby condition.

2) PLAY pinouts: As can be noticed in the diagram, the IC facilitates two PLAY pinouts, which are PLAYE, and PLAYL. PLAYE allows an logic edge activated triggering, while PLAYL facilitates a logic-level activated triggering of the playback.

In the PLAYE or edge activated mode, a single press and release or a momentary press of the button will initiate the playback of the recorded clipping through the speaker, and will end as soon as the internal EOM (end of message) signal gets activated.

The PLAYL mode is activated when the attached button is pressed and held pressed without releasing it. The audio playback now continues as long as the button remains depressed, or as soon as the internal EOM is activated. Keeping the button permanently pressed will cause a higher current consumption of the IC.

Other than the REC and the PLAY buttons, this audio record/playback circuit additionally possesses a couple of switches associated with the chip in the form of SW1 and SW2. SW1 is positioned for the “Feed Through” action while SW2 for the “REPEAT” functioning. Let’s understand them in detail.

As may be witnessed, the SW1 is configured with the “FT” pinout of the IC which refers to “Feed Through”.

When actuated in the feed through mode, the signal across MIC, and the MIC_REF pinouts are bypassed through the AGC pinout of the IC, up to the the filter driver stage and finally reaching the speaker points (SP+ and SP-)

The FT input signal is responsible for controlling the feed through mode of the chip. In order to be initiated the feed through mode, the pinout FT is held at the positive Vcc logic, while the REC, and the PLAY buttons are at low logic or with their buttons in the deactivated positions.

SW2 is used for enabling the REPEAT mode, which implies that when this switch is toggled ON the playback goes on repeating the recorded message clip through the speaker non-stop, until the switch is toggled OFF.



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