Datasheet

Record Playback Essentials
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Record Playback IC Pins on the ISD1820
The following table indicates what each pin on the Record Playback IC does:
Pin No
Name
Description
1
REC
The record input
:
when taken and held high causes the device to re
-
record the message.
The IC contains a pull down resistor on this input.
2
PLAYE
The play (edge
activated) input
:
when taken from low to high, the device plays back the
full message. The IC contains a pull down resistor on this input.
3
PLAYL
T
he play (level activated) input:
when held high, the device plays back the message, if
taken low during playback, playback stops immediately. The IC contains a pull down
resistor on this input.
4
MIC
Microphone input. The microphone is AC coupled to this pin via a series capacitor. The IC
contains amplification, so external amplification is not required.
5
M
IC REF
Microphone reference:
the negative microphone connection, used to reduce noise. This
is also AC coupled through a series capacitor.
6
AGC
Automatic gain control:
used to set the gain of the pre
-
amp. Connecting a 4.7uF
capacitor between the AGC pin and Gnd, gives good all round performance.
7
SP
-
Speaker out
-
:
the negative speaker output signal, min impedance 8 ohms.
8
Gnd
Ground:
the zero volts connection.
9
SP+
Speaker out+:
the positive speaker output signal, min impedance 8 ohms.
10
Rosc
Resi
stor oscillator:
the resistor that sets the oscillator speed. Connected between Rosc
and Gnd. Rosc = 80K gives 8 seconds (min record time), Rosc = 160K gives 16 seconds
(max record time)
11
Vcc
The positive voltage connection, typically 3V but will operat
e from 2.7V to 4.5V.
12
FT
Feed through:
this pin is held in a low state by an internal pull down resistor in normal
operation. However can be taken high if the pre-amp stage needs to be bypassed. In this
case the input signal is feed through directly to the analogue to digital converter.
13
RECLED
Record LED
:
this output is normally
high and goes low during record
for the duration of
the recording. It also goes low upon completion of playback and can be used to make
the IC continually replay the message.
14
Gnd
Ground:
the zero volts connection.