I had some space left on the TinySensor v1.0 PCB, plus I left myself few days to think before ordering the first batch, so I decided to throw in a SD card port. I didn’t want it to be anything fancy like the impossible to solder SMT card slots, so I decided to go for a quite rough but easy solution based on Getto SD card slot idea, also used by Nathan Chantrell in his SD shield project:
Nathan has put up a simple schematic for the SD card pin layout:
So the idea is to use either straight or right angle pins on the PCB and solder the SD card adapter to the PCB, then insert an micro SD card in it.
Here is the modified PCB:
The SD card can be Chip Selected via PA2 or PA7 pin, select-able by a jumper. Basically it is a SPI interface, so any 3.3V SPI device can be hooked, not just a SD card.
Following the fiasco with the first version of the PCB, I have decided to create a single sided PCB so that the DIP socket that was causing me trouble is on the top. Here are the results, the PCB works great and the temperature is being sent every 60 seconds using the DS18B20 sketch.
Apart from the pathetic etching job on the PCB I described yesterday, I found out this morning that I also managed to etch the kitchen sink and made wife unhappy. It have been warned not to pour ferric tri-chloride in it, but few drops seem to have found their way.
I drilled the holes today and tried to solder the 14 pin DIL socket, but of course solder would not pass through the holes since they are not metallic as in a normal PCB. The socket is low and that means I have no access to the top side to apply solder as well, this resulted in bad connections all over. So I consider this project a failure, except for the learning part.
My next steps after I recover from the damaged ego, are to rework this as a single sided PCB and try it over. (114)
As I mentioned in my other post, I wanted to re-do the temperature sensor, this time on my own PCB. Driven by the hunger for instant gratification, I have overcome my fear of home-made PCBs using toner transfer and ferric tri-chloride etching method. Ordering single prototype to a PCB fab house means I have to wait couple weeks, and I
couldn’t didn’t want to wait. So here I am, spending a day on educating myself in the mysteries of home PCB fabrication. After checking out half the Internet on this subject, I laid out quickly my designs in Eagle.
There is an six pin ISP that will be used for programming the ATtiny and later for powering the board. Initially I wanted to insert a CR2032 coin cell battery, but since I son’t have that part, I preferred to leave it. I had a small box that I wanted to accommodate the project, so the PCB is sized accordingly. The PCB is intended for a room node where extreme temperatures will not occur (hopefully), so I will use the TMP36 temperature sensor, not the DS18B20 as my strip board version for the water tank temperature monitoring does.
I made probably 10+ attempts before I could transfer the toner without either smearing it or not adhesing it sufficiently. Another challenge is that it is a double-sided PCB, so both sides must be aligned precisely. I managed by cutting the PCB in exact same size as the paper printout. Finally it worked out and I started etching. I over-etched it as it is obvious but for a first ever attempt, please be forgiving . I tested the tracks with multimer and to my surprise they all work, there is no shorts.
It is late already and I will be doing the drilling and mounting the components another time.
Some pictures of how it worked out: