Subject: [Shop-talk] Need a variable 85-285 ohm resistor

From: Darrell Walker <[email-masked]>
Date: Tue, 12 Mar 2013 15:11:35 -0700

I'm looking at putting a oil pressure gauge in my TR8.  I've decided that an
electric gauge would be preferable over running a line of hot oil into the
passenger compartment.

I've located a Jaguar gauge that looks good in the instrument panel (in place
of the clock), so now I need a sender.  I've identified what I believe is the
correct sender, with the following specs:

0 PSI - 250-285 Ohms
10 PSI - 250-275 Ohms
60 PSI - 85-115 Ohms

(seems like a lot of overlap at the low end!)

Since the sender is around $40, I'd like to verify that it is right for my
gauge, plus I would like to verify the gauge actually works.  To that end,
need a way to setup resistance values in that range.  My first thought was a
potentiometer, but looking at Radio Shack, they are listed as "5K" and "10K"
ohms, but no more details.  I assume these would be 0 to 5K ohms?  That would
make it very sensitive, so I'm not sure that would work well.  There is also a
25 ohm rheostat, but that is too low.  I could get some discrete resistors,
but it would be nice to check that the gauge moves smoothly.  I don't think
that I need to handle much amperage in this application.

So, any other ideas on how to make a cheap test rig for my gauges, preferably
using easy to obtain materials?  I'm a software guy, not an electronics guy,
so I apologize if this is an EE 101 type question!

Thanks,
Darrell

--
Darrell Walker
66 TR4A IRS-SC CTC67956L
81 TR8 SATPZ458XBA406206
Vancouver, WA, USA
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From: [email-masked]
Date: Tue, 12 Mar 2013 18:34:01 -0400

I thought a 300 ohm potentiometer would work but find that a 500 ohm model
is much cheaper.

http://www.ebay.com/itm/500-OHM-Linear-Taper-Rotary-Potentiometer-B500-Pot-/280672832335?pt=LH_DefaultDomain_0&hash=item4159678b4f

> using easy to obtain materials?

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From: Randall <[email-masked]>
Date: Tue, 12 Mar 2013 22:43:06 +0000

Radio Shack unfortunately doesn't carry much in the way of components any more.  You're lucky if they get even close to what you want.

But in this case, I think that
http://www.radioshack.com/product/index.jsp?productId=2062307
will do well enough.  You won't be using its full range, but since it is 15 turns from 0 to 1K, you'll still get about 3 turns between 85 ohms and 285 ohms.

Randall

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