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Code and circuit works great on the bench. Ready for install, but it seems that to ensure a stable install in a a noisy environment, I may be well suited to protect the signals with either components in the circuit, or wiring, or code. I have searched through posts here and some are relevant but some advice either feels like a guess or does not have an explanation.
QUESTIONS (see below for current circuit and details that may help with answers):
- What would should I add to the circuit for filtering or protection?
- Would shielded cable or twisted wires help or be necessary? 24g wires okay?
- 0.10% resistors necessary or 1% is good?
- Why pullup vs pulldown for reference resistor? Should I change?
- Should I have a delay between my 5 data samples for a reading?
I have not calibrated for absolute accuracy, but it reads as expected and the resolution sweeps great at 0.1°.
DETAILS:
- For the 10k thermistors, I use steinhart equation with specified constants, resolution coded to 0.1°c.
- For the 2 Delphi coolant sensors, the spec sheet only has a lookup table, so I fit steinhart best I could and is within 0.1°c through the working range.
- Time constant of fanChange->tempChange creates a PID cycle that requires temperature readings about every 5 seconds, but my display refreshes at 2Hz so that is when I get readings.
- Resolution is more important to me than absolute accuracy (but I'd like to be within 1°c absolute). I just want to make sure transitions are smooth without jitter for each PID cycle at 0.1°c readings.
- Critical working temp ranges have thermistor resistance range from 1,250 ohm->130 ohm and total non-critical range starting at 50k ohm downward.
- Code reads the resistance using 10k pullups and converts to 0-1023.
- Code averages 5 immediate looped readings to get a value.
- I have started wiring with 24g leads from Arduino under dash to thermistors under hood, about 6 foot run and potentially passing some noisy stuff but I'm isolating best I can.
- 4 thermistors & 1 pwm fan signal will all be run through engine compartment where things can get noisy.
THANK YOU for any help. I'm a hobbyist so any detail you can provide with your suggestion would be helpful so I don't screw up your good advice! Exact spec of suggested component, where to wire, and polarity if necessary. Any help received will certainly be passed on as anyone might ask me for help.
- Scott