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Re-wrote the code with a proper stepper motor driver. Added ballistics, acceleration etc. Needle is much better behaved and moves smoother now. ADC is reading dummy data and displaying on the gauge. Ready to add thermocouple interface.
Last edited by dvallis; 02-23-2017, 10:30 AM.
Reason: Typo
"And then we broke the car. Again."Mark Donohue, "The Unfair Advantage"
Neat. The most cost effective method for finding a sensor for rotor surface temp would probably be to tear down a commercially available infrared pyrometer and either find a datasheet on the sensor or reverse engineer the unit it for signal interpretation. You'd need to make a custom housing with an IR-transparent lens though, might be prohibitive if you don't have machine tools, but even then I think it would probably be cheaper to have something turned out on a lathe and weld a bracket to it than the $600 per sensor mentioned earlier in the thread. That's if you must have rotor surface temperature, the commercially available thermocouple embedded in the brake pad is a fine solution you'd just have to account for conduction.
IR measurements are typically inaccurate on shiny, varying surfaces like the braking surface of a disc.
That would only be an issue when something hotter is radiating IR which is bouncing off of your reflective surface, in the case of brakes where they'll be very hot and emitting a lot of IR, there would be no issue.
I'm going with a 2000F thermocouple attached to each brake pad. Much simpler and more robust at the hot end than an IR thermal sensor. Thermcouple does not need cleaning like IR sensor. Downside is thermocouple requires high precision analog front end for sensing, but I know how to build that. Already have a source for bulk thermocouple raw materials so I can make my own for a fraction of retail price.
Built a thermocouple test circuit this morning. Used a precision soldering iron to generate temperatures around 750F and measure it with PSOC. Worked perfectly. Next step is translating the thermocouple output onto the gauge. See video below.
"And then we broke the car. Again."Mark Donohue, "The Unfair Advantage"
What are you going to do about the power supply for the gauge's front end? Going to need some serious filtering with the noise on the car's charging system. If you look at the +12V with a scope and resolve down to μV level it would look like you're watching some heavy metal music waveforms.
From my experience with amateur radio transceivers even those designed for mobile use will pick up noise from the charging and ignition system, it's more difficult to filter that noise when you're drawing tens of amps though, as in the case with a radio that is transmitting. In some cases it's nearly impossible to eliminate alternator noise completely on transmitted audio.
Yes, noise is a problem in automotive electronics. I'm using a 12V/5V DC/DC converter called the S6BP201A1AST2B000. It's a synchronous buck/boost designed for automotive applications. Takes care of surge loads, cold cranking noise and generally turns the nasty thing called 12V in cars to something usable for semiconductor electronics.
"And then we broke the car. Again."Mark Donohue, "The Unfair Advantage"
That's a nice bit of kit. Little ripple on the spec sheet wave form, no problem, will settle down a little under load and if needed be clean as can be with a little bit of extra capacitance on the output.
Thermocouple analog interface is working. Here it is reading my brake simulator (aka Soldering Iron) temperature. It takes about 1 minute to heat up and 5 minutes to cool down. Analog interface has a bias issue that won't let it red below about 90F. Not a big deal since we're interested in HOT, but something I'll solve eventually. Data looks nice and clean though. Declaring Victory and calling it a night.
"And then we broke the car. Again."Mark Donohue, "The Unfair Advantage"
I decided to go with a digital display. I can make it cheaper and there are less moving parts. Should be more reliable overall. Will be something like this, minus the decimal place.
"And then we broke the car. Again."Mark Donohue, "The Unfair Advantage"
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