| After wasting
probably too much money on trying different kinds of meters that were available
in the UK (without any success) I invested in two LCD meters from Datel.
These are the same meters that Mark Munro
uses in his displays and his design is extremely simple. The meter generates
a reference voltage which gets compared to the voltage generated by the
oxygen sensor. The ratio between the two is displayed on the meter, and
this ration can be adjusted with a potentiometer to give a meaningful display.
For example, the sensor generates 10.5mV in air so adjusting the reference
voltage can make the display read 0.21. The circuit consists of the meter,
the input, the potentiometer and a jumper wire across a couple of pins.
Unlike the DPM18s I've been using there is nothing on the board that needs
removed/replaced. The meters also have a backlight which can be switched
on or off. The picture shows a quick test, reading 0.212 for air. |
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Another advantage
of the Datel meters is there size. The DPM128s are huge. As can be seen
in the picture, the Datel meters are almost a quarter of the size of these.
Two of them will easily fit inside the housing. |
| The next step
was to mount two meters on a board with the calibration pots. I also added
a 4-way switch so that the meters can be switched on and off individually
and the backlights of each meter can also be controlled seperately. |
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This is the
back of the board. If I can find someone who can make up PCBs then I will
get a few printed. At the moment all the connections are hard-wired and
the whole thing sealed with silicone. |
| Finally here
is the display mounted inside the lexan housings made by Jake Doktor. |
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