tach adapter

[Don.F.Broadus at ucm.com]

On the factory tach look for a fairly large capacitor (non electrolytic)
,this is usually the integrator cap. Doubling the stock tach  4cyl cap value
gives 8 cyl readings so somewhere in-between will be 6 cly. Check the chip
if it is a LM2917 or close to this number it will be easy to look up the
national semiconductor web page. I have tach circuits for LM3900 OP Amps
that I could Fax you if the stock tach cant be modified. Most new tachs have
an air core meter movement  if the tach needle doesn't go to zero with the
key off. It probably is an air core meter. National has IC's for this type
also. 
  









  

> -----Original Message-----
> From:	cwagner at info2000.net [SMTP:cwagner at info2000.net]
> Sent:	Friday, October 29, 1999 2:44 PM
> To:	diy_efi at efi332.eng.ohio-state.edu; gmecm at efi332.eng.ohio-state.edu
> Subject:	tach adapter
> 
> I have another project that I am working on for a friend.  He has a 
> Toyoyta vehicle that had a 4 cyl engine that he dropped a v6 into.  
> He wants to use the factory tach in the dash instead in getting a 
> new one.  Does anybody have any ideas for a tach adapter to 
> convert a 6 or 8 cyl signal to a 4 or 6 cyl tach?  I am hopping that I 
> could make one thing that can do all this, like convert a v8 or 6 cyl  
> to a 4 or 6 cyl signal in one package by changing some dip 
> switches.  Would a 555 or a op-amp work on something like this.  
> If so, does anyone have any diagrams or schematics?