Instant Replay
the WMS72xx series, a family of 256-tap, nonvolatile,
digitally programmable potentiometer ICs aimed at communications, industrial, and consumer applications; and
the I16xx ChipCorder series of single message
record/playback ICs.
The I16xx is the first series of ChipCorder devices
designed to operate from 2.4V to 5.5V. Furthermore, the
I16xx series features 6. 6 to 40 seconds in record/playback duration, pushbutton operation, LED indicators,
nonvolatile message storage, and an integrated speaker
driver, which provides both PWM and current-mode
speaker outputs. By varying a user-determined external
oscillator resistor, the I16xx series (1610, 1612, 1616,
and 1620) can be programmed for a 4 to 12 kHz
sampling frequency. Likewise, this variable sampling
frequency also determines the length of recording time.
Finally, this is a fully integrated system-on-a-chip with support functions that include: AGC, microphone preamplifier,
speaker drivers, oscillator, and memory. All of this in a
neat 16-pin DIP. Perfect for hacking into an FM radio.
In this hack, we are going to turn an ordinary FM radio
into a digital message center. By inserting a ChipCorder
I1610 device (with support components) inside a radio,
you can instantly record a short message that can be
played back on command. If you elect to switch to a different ChipCorder series IC, you can add several of these
digital recording devices in series and make a variety of
messages that can be individually played back. You are
only limited by the space available inside your selected FM
radio (or other electronic project).
Figure 3. While the prices of these
radios are great for hacking, they
don’t have the best performance.
So buyer beware.
Figure 2. Some ChipCorder
family members. The two
top ICs are I16xx series
chips (e.g., I1610 and I1620,
respectively), while the third
one down is ISD5116 and
the bottom IC is ISD4004.
one record pushbutton. Or,
you can add three pushbuttons. In this hack, you could
use a single edge-activated
playback pushbutton along
with one record pushbutton.
While we’re on the topic of choosing your interface,
you might want to consider adding a separate power switch
for the ChipCorder circuit. Otherwise, the recorded message will only play during operation of the radio. This could
be distracting. I had to omit this switch from my “Instant
Replay” due to space limitations — there wasn’t enough
room inside the radio’s case for holding another switch.
You might have better luck, however. If so, be sure to
Hacking Instant Replay
What Went Wrong
Step 1. Cracking this Oyster. Opening up my cheapo FM
radio was incredibly easy (see Figure 3). I just had to remove
one screw and pry it apart with my fingernails. Be forewarned, however, I have seen some inexpensive radios that
have the cases glued shut. If this is the case with your radio,
use a small knife blade for cutting away the glue from the
plastic. Then you can glue everything back together again
when you’re finished with your “Instant Replay” hack.
While there aren’t very many components in a ChipCorder circuit,
the wiring can be somewhat tricky. Double and triple check your
wiring. If you think that the FM radio speaker and/or your own microphone connections are at fault, attach a spare eight-ohm speaker to the
ChipCorder circuit’s output for checking the speaker connection and
another spare electret microphone to the MIC input for verifying the
microphone connection. Finally, use your multimeter to make sure that
the ChipCorder IC is receiving ample power. The different members of
the ChipCorder family have differing power requirements. Refer to the
ChipCorder Family Members sidebar for more information.
Step 2. Opt for the Pre-Made Board. If you want to
save yourself some time, you can purchase a ready-made ChipCorder recording board (see Figure 4). Just
install this board inside the radio, attach a power supply,
and connect its output to the radio’s earphones socket
or speaker terminals. Otherwise, you can easily and
inexpensively wire your own board. Whichever circuit
you choose, beware of electric short circuit. Insulate
your ChipCorder with some inexpensive antistatic foam.
Step 3. Let Your Fingers Do the Recording. At the
least, you can build a ChipCorder circuit with only two
pushbuttons — one playback (e.g., either PLAYL; level
activated or PLAYE; edge activated) pushbutton and
SEPTEMBER 2005
Figure 4. This prebuilt Winbond
I16xx evaluation board is great
for quickly adding an “Instant
Replay” recording circuit to
any electronic project.
Figure 5. My “Instant Replay”
circuit had to be mounted
externally on my FM radio.
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