>Unfortuantely, on the ISD1000 (I don't know about the others), when the
>chip is not playing, both outputs are forced to ground. Using one for a
>single-ended output produces a "thump" when the chip starts and stops
>playing.
This is true of all the chips.
{Quote hidden}>>>Also, any ways to copying the recordings from one ISD chip
>>to another?
>>
>>The only way that i am aware of is at the analog level - 1
>>chip is set to play back and the other records. This is not
>>ideal but you do not have access to the inner workings of
>>the ic.
>
>This is generally the process. Of course, don't use the microphone
>amplifier and AGC on the destination chip. Put a gain adjustment between
>the two chips and adjust so both reordings are the same level. You
>should use the external clock feature to clock both chips at the same
>rate. The recordings should then end up at exactly the same address,
>regardless of variations in the internal clock generators. If preserving
>the signal frequency content is more important, use the internal clock
>generators. The clock rate can't be increased to speed up the process
>because the analog lowpass filters in the chips are not driven by the
>clock, so they would excessively filter a faster-sampled signal. ISD
>mentions they sell a box to replicate a chip's content either singly or
>in gang. I didn't see any details about the "programmer"'s availability
>or price.
There is however a subtle issue when copying chip to chip which may
be a problem in some applications. When you stop recording, record
continues to the end of the segment (50ms). There is also a delay
between starting playback and the playback actually commencing. What
this effectively means is that if you copy from chip to chip, the
copied message will tend to be one segment longer than the original.
I've found that you can do chip to chip copying at least 4 or 5 times
between chips with no noticeable drop in quality.
For the analogue interface, you need to use a differential amplifier
to avoid the abovementioned clicks at the start/end.
The cct below gives the correct level for chip-chip copy on ISD14xx
parts:
+>9V
|
|---[10K]-------|
SP- --[10K]---[ - | | 1uF
[ 1/2lm358 >--------[22K]----[]|--->AIN
SP+ --[10K}---[ + |
| | 1K
10K | |
| GND GND
+5V
Note that the lm358 is assumed to be running from at least 9v, so the
5v reference is far enough from either rail for sufficient swing.
For a 5V-only system, you should be able to connect the + input of the
opamp to the junction of two 20K resistors, one to +5v, one to 0V
____ ____
_/ L_/ Mike Harrison / White Wing Logic / .....wwlKILLspam
@spam@netcomuk.co.uk _/ L_/
_/ W_/ Hardware & Software design / PCB Design / Consultancy _/ W_/
/_W_/ Industrial / Computer Peripherals / Hazardous Area /_W_/