It was a rainy day today so I finally had the time to render the kitchen into a second electronics workshop and solder the All-Out-Board I designed.
Apart from the fact that SMT parts are a real pain in the gluteus maximus, more so if you’re 40+ years old, things worked great. I discovered that I by now have difficulty seeing the normal sized pins and wires with my everyday glasses. Not funny.
Back to topic. The board soldered very well. To cope with the SMT parts I manufactured my own solder flux from rosin and Isopropyl alcohol. I made a mixture of 1/2 rosin and 2/3 Isopropyl alcohol and filled it in a little bottle that has a brush in its cap. Please be aware of the following: Isopropyl alcohol is a chemical substance. DO NOT DRINK, DO NOT SPILL, DO NOT APPLY TO SKIN UNDILUTED (minimum dilution 50/50). And of course, make sure you do not violate local laws when trying to buy this stuff.In Germany you can get Isopropyl alcohol at the pharmacy. If asked, take the 100% pure stuff. And again: It has the word “Alcohol” in its name, but it is poisonous. DO NOT DRINK. Rosin (or colophon or Kolophonium [Germany]) can be bought at music stores where they sell instruments. It is used by violinists on their bow strings to increase friction between the bow and the string of the instrument, thus producing a clear tone.
Take a look at the picture with all the SMT parts soldered on. The board has not been cleaned in this picture. Generally it is a good idea to clean excess flux immediately with isopropyl alcohol and lots of Kimwipes.
As happy as I am that the board is, in fact, working as designed, I made a couple of design errors. One can be seen in the picture above. Take a look at the circle on the left. This is where the buffer battery (a coin cell) for the real-time clock (RTC) has its place. Notice the text? Yes, the positive side of the battery goes on the board which is not really how coin cells on PCBs normally “behave”:
Positive side is up. It is even engraved on the coin cell holder I am using on the board. So what happened here?
I changed to another coin cell holder in the middle of designing the board. The original holder was a plastic one where the coin cell would fit in and had two pins to be soldered on the board. But this holder was not in stock at my supplier so I changed. And didn’t correct the schematic and the board accordingly (I just changed the part outline on the board). But no harm done, with a piece of aluminum foil and the coin cell put in upside down (plus down) everything works fine.
Second, well, it’s not an error, I could have used the DS1307-chip (the black rectangle next to the battery outline) in normal dimension, not as an SMT part. There would have been enough space. And I wouldn’t have spent 45 minutes searching for the marking on the SMT-chip that should show where pin 1 is. Usually there is a white dot or white line printed on the circuit, or a small dent is clearly visible. Nothing with this chip. After looking at it under indirect light with a 20x magnifying monocular I discovered a small dent at the edge of the chip, just at the connector. This had to be it. And luckily it was.
Look at the complete board with all parts on it and all jumpers (the green ones) configured for pin output (I used a wide-angle macro lens, so the parts on the outer sides look like they are bent outwards. They are not!):
The third design “flaw” is with the pin header on the lower left that connects the Raspberry Pi. Pin 1 is the left one on the bottom line. This is not crucial, but to connect my board and the Raspberry Pi the flat ribbon cable need to be twisted.
But, again, it works. I made a small video to show it but just discovered that I can’t upload videos to my blog. So I created two animated GIFs (sometimes it’s good to be old-school…). Sorry for the bad quality.
This is the output of my first test program to quickly check if things are working. On the left, you guessed it, “Blinken”, and on the right it’s “Cylons” or “Knight Rider”, whatever you prefer.
So this concludes part 2, which is sort of a proof of concept. I am in the process of documenting my “All-Out Board” in case anybody wants to build one.
I do have some spare PCBs, so if you are interested please feel free to drop me a note.