Voice record/playback circuit

[bluedishwasher]

hey guys i'm looking to do a voice record and playback circuit. what i'm looking for is jsut something simple that uses an ADC-->microprocessor-->DAC
what i'm looking to do is convert an input signal from a microphone to digital to be stored in the microprocessor and then converted back to analogue and outputted through a loudspeaker. if anyone had any circuit diagrams or suggestions much help appreciated as i am very confused by numerous datasheets i have seen!
regards,
George

 

[HarveyH42]

SAW 3 DIGITAL VOICE RECORDER | AllElectronics.com

$2.00, batteries included, interfaces well with a microcontroller, 30 seconds record/playback. Works well on 3.6 volts.

Using just a microcontroller isn't quite so simple, but can be done. There is a PIC project on the web, but you'll need to find it. I don't use PIC myself (for obvious reasons), but check out the projects occasionally.

 

[Analog]

You didn't mention several key parameters.

1. sampling rate
2. resolution
3. time of recording
4. amount of memory you have

Otherwise buy Harvey's.

 

[3v0]

Simple hardware can mean a lot of software work. See the Mondo site for details for a neat method that uses a digital pot as a DAC.

The purpose made chips can save a lot of work. Futurlec has several.

 

[bluedishwasher]

hi there, thanks for the brilliant responses.
in response to analog the circuit needs a sampling rate of only around 20khz, it does not need to sound amazing. the time recording required needs to be between 10 and 20 seconds. i would be interested in this pic idea although i can not find anything on google?
i have not purchased any memory yet as i have not been able to locate any stand alone chips, however could i not use the onboard memory in a microprocessor?
regards
George

 

[Mikebits]

hi there, thanks for the brilliant responses.
in response to analog the circuit needs a sampling rate of only around 20khz, it does not need to sound amazing. the time recording required needs to be between 10 and 20 seconds. i would be interested in this pic idea although i can not find anything on google?
i have not purchased any memory yet as i have not been able to locate any stand alone chips, however could i not use the onboard memory in a microprocessor?
regards
George

Well, you should do the math. 20KHz sample rate means that for every second, you will have sampled a waveform 20,000 times. Now depending on your A/D that can be 8 to 16 bits per sample. With 8 bit, we have 160,000 bits being stored/sec or 1.6 million bits/10 sec. Figure an 8 bit memory device so 1.6 million divided by 8 gives about 200Kbyte of memory. Add on code memory and other bits that I missed and you need about 256 kbyte of memory for 10 sec, not including code.

Someone should double check my numbers as I have been drinking hic...

 

[Analog]

Someone should double check my numbers as I have been drinking hic...

That just means you're probably right!

 

[3v0]

The examplae on Mondo Tech I mentioned in my first post uses a PIC but the sample rate it 8KHz. Select speach EEPROM from the sidebar.

 

[HarveyH42]

Guess I was mistaken. Searched, and found the project, but it's only to play, not record...
Official Home Page of the Roman Black

Might help you see what you getting into, and might give some direction. Obviously a PIC is barely up to the task of playing the audio. Maybe it was an AVR projected that did the playback and recording... (just kidding)

 

[3v0]

The Roman Black is 1 bit recording. It is interesting but about the lowest rung on the ladder.

 

[radiofanatic]

How about this schematic Voice, sound recorder circuit schematic it looks to me that is very good but I dont know if you can find the IC...