Part Prices

I was looking at laying out a prototype board, something better than the proto board I am using now. I really like the MAX6675 for the thermocouples. The protoboard is looking good with 4 of the Arduino modules on there. I've built some braces for the modules, and it should be good for ground testing. 

I can buy the Arduino modules with the cap from the data sheet, 0.1" pins and a screw terminal for about $4.00 all day long. If I want to buy the bare chip, it is $9.00-$11.00! Why? I thought the Arduino modules might be using a clone chip, but when I magnify the chip, it clearly says MAX6675ISA. Is it counterfeit? I would thing MAXIM, or whoever would be catching these at customs if that were true. I just don't get it. 

I need to do some more research. Find out if there is some magic I am missing. I am sure I could request samples, and probably get what I need for very little, but if someone were to want to reproduce my work, well, it could get very expensive. 

I know I said I ordered 3 meter thermocouples, I was wrong. I ordered 2 meter cables, and boy are they long! I could have gotten away with meter and a half cables for the two front (rear) cylinders, and 1 meter for the back cylinders. Anyway, they aren't built well, so I may need to modify them anyway. The crimp joints don't have any strain relief, and that is where things are likely to break. I 3D printed a brace to support the modules.

The code has been modified for talking to all 4 modules. I think I'll only have 4 on this board, due to space. Eventually I'd like to use 4 more of the same module for the EGT temperature measuring. I am also using the Hall Effect Linear Current Sensor Module ACS712 for Arduino for measuring current to the panel. I haven't the software for that yet. 

I am printing a proto mount for the firewall now. I use tinkercad for these parts. The links are here, if you want to use them. Let me know if you do. 

ProtoMount                       ModuleBrace

      

The Mask is Off By One

A common software mistake, off by one errors happen occasionally. Indexing starting at 0 instead of one, you got ten things, so the last on is 9, not 10. What about hardware, you go pins, and they are numbered, or sometimes labeled. Dang it, wouldn't you know it, the labels on the board were off by one.

If you look at those labels, you can see the ground and 3.3V labels and that is where I am connected. Trouble is, if you look on the board this shield plugs into, the labels are off by one.

Starting with the pin labeled 5.0V on the shield, that is connected to RESET on the MEGA128 board that I am using. The next pin, is labeled  3.3V, but the traces in front of it are connected to the 5V. The next pin, labeled GND but the trace in front of it is really 3.3V. See these two pictures.

I believe I may have cooked my chip. All I could get out of the code was a 0. Over and over again. I should check the other writing to make sure I am connected to the proper pins. 

I have a spare MAX31855, so I am not totally dead in the water yet. I want to connect it to the right voltage, incase it does a shutdown on over voltage, and not leak smoke only. (I never saw any smoke).

Unsoldering the chip may be possible as well.

I really am trying, I just kept fiddling with the software, until tonight when I checked the voltage. (trust me the software is monkey see monkey do. I am using the SPI library included with the Arduino code.

I am an idiot. The 50, 51, 52 ... pins at the end start with 2 ground pins. I didn't count. So it is completely wired wrong. I need to take another whack at that part before I get around to calling my chip bad.

I am blaming it on being out of hardware practice. Can you take 5 years off from something and pick it up in a weekend.

Ever be so dumb yourself?

I re-did the connections. I am, using the ICSP header for both the SCLK and MISO. I've got it connected to 3.3V and it seems to be outputting data. 0 with nothing connected and some random data when the thermocouple is connected.

I've found the Adafruit libraries for the MAX31855, and want to try them, but am out of time for tonight. I'll get to looking at them another evening when I have more time.