29 Aug 2010

For some reason I had a mental block on wiring up the oil temperature and pressure sensors. Don’t know why since the issues creating all the angst are resolved. Today it was like having pushed off the yucky vegetables until last. Anyhow, some time back the sensors were calibrated, so with the resistance values on-hand the scalings were entered into the dash. Then there was snaking the new wires through the existing harness, a reminder than it isn’t done until it’s done. The wiring behind the dash had to be changed, too, adding the additional inputs I’d failed to plan for.

Race Technology references sensor readings to 5 V, and trouble starts when using cheap sensors like the ones used with pointer gauges. The trouble is that the cheap sensors tend to have very low resistance at one end of their scale. Race Tech provides a +5V voltage reference for the sensors, but they conveniently assume users will use the expensive sensors that have higher resistance (that they just happen to sell.) For that reason they used a weenie voltage reference capable of only outputting 50 ma (0.05 amp) and unfortunately, using just one low-resistance sensor means it may draw 50 ma on its own, leaving nothing for additional sensors. Soooo, higher power precision voltage references were going to be added, capable of supplying 150 ma apiece, but I forgot I’d need perf board or circuit board material. Whining aside, that’ll be picked up this week, the reference wired in, and the issues will be put to rest.