Wednesday, March 14, 2012

I may finish this yet...

I've quit and come back before, but not so long. Actually, I got some feedback a month or so ago. Someone was offering a suggestion on the thermocouple hardware. Bill offered:

  Analog Devices chips that make thermocouple interface a whole lot easier. What 
 are your thoughts on this. 
  PS I like the Dangerpants ADI(air data system)

I think the analog devices are about the only ones I didn't consider.  They are about $5.00 each, and only available in SMT packages. They sure look like they are easy to use, but at that price, it might be a challenge without multiplexing the the inputs.

There is the Arduino Thermocouple Multiplexer Shield that will take 8 K type thermocouples in (4 cylinder EGT/CHT monitoring eh?). Well, $49 puts it in the 8 individual interface chip price range. It is already assembled, so it might be a solid option. The page shows the chips that are used to do the conversion are the MAX6674/6675 chips which are about $12each, and they talk SPI (not supported directly by the Arduino). But the multiplexer the board uses is the ADG608, which is about $5 in homebuilder PDIP packaging.

Over the summer and into the fall I was thinking I'd like to build my own 3D printer. I get the Sparkfun 4 channel stepper controller. It works, but not in bus mode. My thinking was, bus mode would save a lot of wiring, but alas, I had to use a lot of wire to get even 3 steppers going. It isn't a shield, it was all point to point wiring.

I am trying to get the Android SDK components installed on my laptop while I type this in the other window. That is taking a while, so I can go back to working on this blog. The download speed is screaming along at about 125K ick! Anyway, that will get installed, and then I can start working on the GUI for this.

I still want to do the 8 thermocouples, for the CHT/EGT monitoring. If I had a 6 cylinder, I'd still do 8 channels for thermocouples, 6 for the CHTs, and 2 for the EGT. The actual EGT doesn't really matter in a carburetor equipped engine. You want to see peak temperature, and adjust the mixture around that. Knowing if there are differences isn't really important, other than maybe to know if there might be something up with the sensors. (I know, in a fuel injected engine, the EGTs will tell the state of the individual injectors).

I want to also monitor RPM. This can be done multiple ways including:
  1. Spark Plug Firing
  2. Mag/EI outputs
  3. Pulse measuring with sensors on the engine
  4. Optical measuring the propeller.
What I thing the design will allow is some external circuit to present pulses in. This will allow multiple choices of one of these options to be chosen by the builder. I have an EI (PMAG) that has a tach output, that I will probably use.

Pressure sensors are already available on the engine to measure fuel and oil pressures. These will output between 0 and 12volts. The sensors will need to be calibrated, and probably can run in parallel with the analog gauges to do so. Same with the oil temperature sensor, it exists, and can probably run in parallel to allow calibration with the new system.

Again any thoughts or ideas, let me know.

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