Bill;
The only issue with that method may be the .7 volt drop between each
diode. What will that do to the accuracy of the tach reading?
Ed Barnard
Bill Babcock <BillB@bnj.com>@autox.team.net on 08/08/2001 11:11:26 AM
Please respond to Bill Babcock <BillB@bnj.com>
Sent by: owner-fot@autox.team.net
To: Ian Cowie <ianhome@acohs.com.au>, FOT <fot@autox.team.net>
cc:
Subject: RE: Smiths tach
I'd use steering diodes externally to make it impossible to connect it
incorrectly. Basically you make a full-wave rectifier and connect it to
the voltage inputs for the device, then cover those inputs with epoxy or
some other insulator and provide only the inputs to the rectifier for
connecting the power. The lead from the coil os a pulse and probably it's
polarity doesn't matter. This way whether someone connected the power
forwards, backwards, or even applied AC it wouldn't matter. If you want to
go overboard you can add regulation so thy can't screw up the voltage. You
can actually get all that functionality in some integrated circuits, or
you could make it from discrete components.
Most good quality electronics come with some of this stuff built in. Even
the cheap stuff usually has blocking diodes to keep you from toasting the
gear.
-----Original Message-----
From: Ian Cowie [mailto:ianhome@acohs.com.au]
Sent: Wednesday, August 08, 2001 3:10 AM
To: FOT
Subject: Smiths tach
Hi fellow FOTers',
Just been given by my friend and mentor (Chris Swingler) his 10,000 RPM
Smiths tach he ran in his Spitfire back in the seventies. I am privileged!
The tach has no markings other than it is Smiths from UK and four
cylinder.
I do not have a hook-up diagram, however, more importantly because of the
period it is POSITIVE earth. As an old sparky I know what that means and
what to do. However, I would much prefer if it were at all possible to
reverse the polarity 'cos you can never fully rely upon the other fellow
understanding the significance or difference for that matter and we will
run
negative earth.
Can any one help with this, otherwise it is into the old plastic tube etc
etc.
Regards to all, and yes we are progressing sloooooowly, pre-fitting stuff
like manifolds and stuff - getting ready to paint - and so on. One day I
will put it all up for you to see.
Ian
777
TR4A
SuperSpit
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