FM Scanner IC

D

Denis M

Guest
Curiosity drives me to ask what IC all those throwaway cheap FM scanner
radios
are based on. At their cheapest they are promo keyrings.....
I have one that has failed. It has an IC that seems to be marked TDA 7888 J
(or T) . 317840 DnD9709
Possibly Phillips logo and marked THIALAND. And that guessed at under a
strong magnifiying glass ;)

Why do assemblers seem to scratch off all markings ? Is it so competitive
out there that even in the cheapest assembler in China must protect
against being ripped off by his neighbour ?

Den
 
"Denis M" (dmahony@iol.ie) writes:
Curiosity drives me to ask what IC all those throwaway cheap FM scanner
radios
are based on. At their cheapest they are promo keyrings.....
I have one that has failed. It has an IC that seems to be marked TDA 7888 J
(or T) . 317840 DnD9709
Possibly Phillips logo and marked THIALAND. And that guessed at under a
strong magnifiying glass ;)

Why do assemblers seem to scratch off all markings ? Is it so competitive
out there that even in the cheapest assembler in China must protect
against being ripped off by his neighbour ?

Den
Click to expand...
You need to be more descriptive. Your subject header suggests a traditional
scanner, ie one that covers two way radio frequencies.

You're talking about those $1.99 FM broadcast radios that tune up when you
press the scan button. And go down to the low end of the band when you press
the reset.

The IC is a variant on the old TDA7000, which converts down to about
70KHz where active filtering can be done relatively easily. Not
the greatest of radio schemes, but suitable for a lot of cheap stuff.
The IC in these new radios adds the circuitry for that two button tuning
scheme.

The IC is in fact the Phillips TDA7088. Datasheet is here:
http://www.semiconductors.philips.com/pip/TDA7088.html

I discovered it when I bought one of those $1.99 radios, and looked
up the TDA7000 datasheet, just in case that was in. Pin count didn't
match, but then the website pointed to some similar ICs, and the 7088
was a match (and once I knew what the IC was supposed to be, the weak
print clearly showed that number).

The tuning is analog, the scan button starts a ramp voltage that
tunes the local oscillator of the radio. Then there is some circuitry
inside the IC that senses a signal, which stops the ramp. Press scan
again, and the ramp starts, at the voltage where it stopped, and so
forth. Pressing the reset button sets the ramp voltage 0.

My take on the marking was that it was just cheaply manufacturered.
I suspect some of the ICs may even be knockoffs. I remember getting
ICs from Polypak decades ago, and they tended to have those weak
markings, while most manufacturers are proud to mark their ICs.

Michael
 
Thanks Michael,

That's exactly it

Regards

Denis

"Michael Black" <et472@FreeNet.Carleton.CA> wrote in message
news:chb176$6kk$1@freenet9.carleton.ca...
"Denis M" (dmahony@iol.ie) writes:
Curiosity drives me to ask what IC all those throwaway cheap FM scanner
radios
are based on. At their cheapest they are promo keyrings.....
I have one that has failed. It has an IC that seems to be marked TDA
7888 J
(or T) . 317840 DnD9709
Possibly Phillips logo and marked THIALAND. And that guessed at under
a
strong magnifiying glass ;)

Why do assemblers seem to scratch off all markings ? Is it so
competitive
out there that even in the cheapest assembler in China must protect
against being ripped off by his neighbour ?

Den



You need to be more descriptive. Your subject header suggests a
traditional
scanner, ie one that covers two way radio frequencies.

You're talking about those $1.99 FM broadcast radios that tune up when you
press the scan button. And go down to the low end of the band when you
press
the reset.

The IC is a variant on the old TDA7000, which converts down to about
70KHz where active filtering can be done relatively easily. Not
the greatest of radio schemes, but suitable for a lot of cheap stuff.
The IC in these new radios adds the circuitry for that two button tuning
scheme.

The IC is in fact the Phillips TDA7088. Datasheet is here:
http://www.semiconductors.philips.com/pip/TDA7088.html

I discovered it when I bought one of those $1.99 radios, and looked
up the TDA7000 datasheet, just in case that was in. Pin count didn't
match, but then the website pointed to some similar ICs, and the 7088
was a match (and once I knew what the IC was supposed to be, the weak
print clearly showed that number).

The tuning is analog, the scan button starts a ramp voltage that
tunes the local oscillator of the radio. Then there is some circuitry
inside the IC that senses a signal, which stops the ramp. Press scan
again, and the ramp starts, at the voltage where it stopped, and so
forth. Pressing the reset button sets the ramp voltage 0.

My take on the marking was that it was just cheaply manufacturered.
I suspect some of the ICs may even be knockoffs. I remember getting
ICs from Polypak decades ago, and they tended to have those weak
markings, while most manufacturers are proud to mark their ICs.

Michael
Click to expand...
 
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