The Usual Tech Ramblings

Tinkering with Temperature (Part Deux)

As a follow up to the previous Tinkering with Temperature post, here is more on what I did, and how.

I made some alterations to my original schematic, as I was originally going with a serial to RJ45 conversion. I figured I’d save myself some headaches, and use one of the Cisco console cables I had laying around1. This had a slightly different pinout on the RJ45 end, compared to the serial cable I was going to make. Pinouts for the cable can be found all over the internet, including Cisco’s own site, but I used this as a reference.

Temperature Sensor Board Now I had my new schematic, I put it onto a board. As with my schematic, KiCad helped out here too. It mocked out the basic components, I just had to rearrange them, and then draw tracks. I did read somewhere that there is an auto-route feature, but I couldn’t find/figure it out, not that mine was complicated, and I couldn’t figure out a few lines. So I ultimately ended up with the image to the right.

Image Once drawn out, a simple case of printing on special paper, or you can do it the cheaper way of using magazine pages. I went with the later. When printed, it’s just a case of taping the paper to the board, and applying heat.

Ironing PCB When applying heat, you must remember to turn off the steam options, otherwise it won’t work properly. This can take some time, depending on the toner, paper thickness, and the iron involved. Once you’re satisfied with enough transfer, time to get the paper wet. This will dissolve the paper, but leave the toner on the board.

Board Inspection Now is a good time to inspect the board, and make sure that any missing traces are covered. Usually you can get away with a sharpie, but you can get special etch-resistant pens. I went over all the lines again just to make extra sure.

Trim PCB At this point, we could etch the board, but it’s still a little large, so I trimmed off the larger side, and left the shortest excess attached. This gave me a good point to hold, as well as a good indication of how well it was going.

Now it’s etching time. Following the instructions carefully, I did this outside in a well ventilated area2, with poor light. Okay maybe I cannot follow all instructions well, but I did wear gloves, and did this away from anything metal.

Etch Board After about 15 minutes of agitation3, and careful inspection, the board was etched. Note that part of the board wasn’t etched in the picture, but that was part that was in the excess area. Another quick trim to remove that excess piece, so it’d fit nicely into the housing.

[Drill Holes11 I borrowed Jeremy’s drill4, and a bit from Rick5. I quickly drilled the parts, and got to work soldering6. One thing to note is that when soldering, and constructing, follow your diagrams closely. I originally soldered one of the diodes in backwards, so it wasn’t working until I desoldered it, and put it back in correctly.

Case Compare I’d carefully designed the size of the PCB to be oversized, I could have clearly chopped an extra inch or so off, because it was to fit inside an old Linksys workgroup switch box. This ended up being about 4x6. The RJ45 connectors were a little low profile for the case, but it doesn’t matter too much, as it’s going to be hiding in the server room away from careful inspection of most people.

Final Product The final product looks like this. Sits nicely inside the chassis, and looks pretty good. It was a 5 port workgroup switch, with port 5 being disabled if you had an “uplink” cable in place. In my case, port 6 is going to be the serial port.

Now for Monday, build some cables, once I’ve figured out all the lengths I need. I did do a quick breadboard test with a RJ45 connector, and 2 wires crimped down to a breadboard to ensure it was working, and got good readings (compared with my fluke tester).

I’ll power additional pictures once I have all the cables in place, and tucked into the racks.

  1. We probably have a draw with about 7 of them in at the office 

  2. At 2200 one night isn’t the best time, but I was eager to get it done 

  3. That’s me getting agitated that it’s not going fast enough 

  4. I really do need to get one, and maybe a small Dremel with stand too 

  5. Not many people have tiny drill-bits but he apparently has a huge kit of them 

  6. Sorry, no pictures of me soldering today