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

      

Chips Are Getting Smaller

I started building with integrated circuits in about 1976. Radio Shack started carrying the 7400 series chips sometime around then. In school I had learned about half and full adders, so I knew what AND, OR and NOT gates were. I imagine they were a couple bucks each back then, but I wanted to build something. I quickly soldered up a half adder using these chips on a piece of Formica, dead bug style.

Over the years I built many projects hand soldering huge boards of chips. In high school, me and three other guys (Scott and Steve) built Don Lancasters TV Typewriter II. We etched the board our selves, but without plated through holes, ended up soldering sockets on both sides of the board (Steve pulled his hair out troubleshooting the thing, eventually removing about half the sockets, soldering the chips in, on both sides). I built many expander boards for the various computers I've had in the last 40 years.

Tonight I soldered in the MAX31855KASA chip I got as a sample a couple months ago. Fun, cool, challenging. I cleaned the heck out of the soldering iron, had to refile the tip to get it sharp enough, and it happened. The first time, I got 4 of 8 pins, the second time I got 6 of 8, and finally with some heat, I got the other two. It doesn't look pretty, but it works, and no shorts. Mass production will require solderflow, if I am to use these chips.

Yesterday and today, I did some research. Yes, the Arduino supports SPI. There is a nice SPI reference library as well. The MAX31855 only does serial out, so I connected the pins like:

   44  - IO44  - Chip Select of the 31855
   50  - MISO  - Serial out of the 31855
   52  - SCK - Serial clock input of the 31855

I used my standard color coding, that I have been doing for over 30 years:
   Blue - Ground
   Red - Vcc
   White - Signal

Then the rainbow ribbon cable is:
   Red - T+ Thermocouple +
   Orange - T- Thermocouple minus

The results look a little messy:
   

I am a little nervous that the chip is at one end of the board and the SPI is at the other end, but that is the layout of this proto board. There is only one thermocouple input in this chip, so that also disapoints me, but who knows, working in eagle, and maybe it won't matter. 

I tested the K-thermocouple that I have using a soldering iron and my vold meter. It is hard to read the voltage in the meter, but it looks like 15mv:

I haven't written the code yet, but I'd like to as soon as I can. Maybe tomorrow.