June Birth Magoncia

user Electronics Engineer

city Innovuze Solutions, Inc.


  • 240 Seconds Voice Recorder

  • Created: Apr 11, 2016

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Summary

This reference design features a 240 seconds voice recorder that is based on SPH1642HT5H-1 and ISD17240PY devices. The SPH1642HT5H-1 is a top port silicon microphone that has a built-in acoustic sensor, low noise input buffer, and an output amplifier. This microphone has a frequency range of 50Hz up to 10kHz. It has an output impedance of 500Ω and operates with a 1.5V-3.6V-power supply. The ISD17240PY device is a single-chip that can record and playback voices up to 240 seconds. It has an on-chip oscillator, microphone preamplifier with automatic gain control, an auxiliary analog input, anti-aliasing filter, Multi-Level Storage (MLS) array, smoothing filter, volume control, Pulse Width Modulation (PWM) class D speaker driver, and current/voltage output. The device operates with a 2.4V-5.5V-power supply.


In this design, the output of SPH1642HT5H-1 is sent to the auxiliary analog input (AnaIn) of the ISD17240PY device instead of the differential microphone inputs (MIC+/MIC-) since the output is designed for single-ended inputs. The AD8515 op amp amplifies the output of the microphone to drive the auxiliary analog input (AnaIn) of the ISD17240PY. The capacitor C1 acts as a coupling capacitor and with resistor R1, acts as a high-pass filter with a cut-off frequency of approximately 40Hz. The variable resistor R2 adjusts the gain of the AD8515 op amp. In this circuit, the ISD17240PY device is configured to record using its auxiliary analog input (AnaIn) via push-button controls. The seven pushbuttons are for record, play, erase, forward, volume, feed-through, and reset functions. The header J1 extends the SPI port of the device wherein the user can access any location inside the memory array of the device or the analog path configuration (APC) register, which allows flexible configuration of audio paths, inputs, outputs and mixing. The ISD17240PY device can have its output sent to the speaker and to the AUD/AUX output pin simultaneously. The AUD/AUX output pin allows the recorded voice to be amplified by a louder audio power amplifier. The RCA connector J2 serves as a source to an external audio power amplifier.


This 240 seconds voice recorder can record over 100k cycles. It can retain a recorded voice message for about 100 years. Also, the ISD17240PY device automatically power-down after each operation cycle, which saves power especially when it runs from a battery source. This reference design can be used in a situation wherein the user needs to record a short voice message in a business meeting, interview, investigation, etc.

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