DIY-WB02 display

[Clare Snyder]

Thanks to Bruce Roe for his input and listening ear, I think I have solved
my display connundrum for my DIY-WB02 test unit.
I have a lab grade milliameter mfg by Yokagawa in the mid seventies -
somewhere around 5 inches square- with a nice mirrored scale, sensitive to
0.1ma full scale.
By putting 14250 ohms and a red LED in series with this meter, it will read
1.3 to 2.8 volts - just about perfect for our purposes. By adding a 25000
ohm resistor in series for free air calibration, it will read  roughly 5.25
volts full scale, and a switch will short that resistor out for normal
operation.
14.4 will be roughly 3/4 scale.
If I do not compress the scale, and let the meter read from 1.4 to 4 volts,
14.4 will be center scale and the operational range will be roughly 3/4
scale. Either way it sounds good - what say you?
The circuit board will fit right inside the case - the 5 leads for the
sensor will attatch to the existing 5 binding posts. A set of power leads
will need to be added.
Now - another question. Aside from the heater current, how much does this
baby draw? Reason I ask is, could we (I) add a 1.5 volt battery inline with
the power from the car to get the board voltage to stay consistantly above
13 when running off battery?

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