tachometer question v8-v6

[Terryk]

I just did a search on LM1819 and there it was.

Terry

----------
> From: Ludis Langens <ludis at netcom.com>
> To: diy_efi at efi332.eng.ohio-state.edu
> Subject: Re: tachometer question v8-v6
> Date: Thursday, December 11, 1997 4:38 AM
> 
> Terry K <terryk at foothill.net> wrote
> >The LM1819 stuff is on the net at National Semicompactor. The tach
schemo
> >is in the data sheet. But it is PDF. 
> 
> Where?  I looked on the National web pages a few days ago (when this part
> was first mentioned.)  I couldn't find mention of an "1819" - either with
> the search engine, or by browsing.
> 
> Adding some useful info:  Some time ago I traced out the schematic of the
> tach in my car.  It uses a 16 pin chip - perhaps this LM1819.  First
there
> is a freqency to voltage stage.  Then there is an (analog) voltage to
> dual coil gauge driver stage.  The FtoV works with an RC circuit.  The C
> is probably 0.033 uF.  The R is on the top layer of a hybrid resistor
pack.
> It looks laser trimmed.  Considering that the cap needs to have a low
> thermal coefficient, I'd change the resistor when converting a tach.
> (Unless you're a tech at NASA or someplace...)
> 
>                    unsigned long BinToBCD(unsigned long i) {unsigned long
t;
> Ludis Langens         return i ? (t = BinToBCD(i >> 1), (t << 1) + (i &
1) + 
> ludis at netcom.com                 (t + 858993459 >> 2 & 572662306) * 3) :
0;}