2017-05-20 (Sa) Weekly Summary

Tim and I have been doing a three-part series on human longevity, this time through medical means. Our third episode was about extending life by stopping and reversing the effects of aging. If you think science has played God in the past...
It may be beyond the lifetime of anyone reading this but it sounds like the next generations may watch their great-great-great-great-great-great-grandchildren graduate college.

Brian - Left _____ Tim - Right

Circuit board etching is a pretty straight-forward procedure. It is simple enough that small errors may not lead to failures and some large errors can still be corrected. It is relatively inexpensive so even a catastrophic error may simply cost time. The most dangerous aspect is the acid used to  strip away the unwanted copper.

The transfers made with a laser printer worked well but there were a couple problems. The first problem was that footprint pads for the transistor were too large. This was a problem with the footprint, not the printing or the process. It was a simple matter to cut away the unwanted toner with a sharp blade. Another problem, this time with the transfer process, was that a couple of the traces were broken. In other words, the toner was not present where it should be. This fix was even easier because a simple Sharpie marker can fill in those gaps.

Making the circuit board at home allowed me to find problems like the transistor pads so the problem can be fixed before boards are professionally manufactured.

Fixing a bad footprint

A different recipe for the etchant, a chemical solution for removing copper, was tried. Normally, ferric acid is the fluid of choice but a bit of advice from the internet said that a mixture of hydrochloric acid and 3% hydrogen peroxide would etch a board as quickly, or more quickly, than the traditional recipe.

I mixed the ingredients in the wrong proportion and had no luck etching a board. Shown below is a picture of the proportions I used but the correct recipe should be 2 parts hydrogen peroxide combined with 1 part hydrochloric acid.

Don't follow the proportions shown in this picture

Before I realized that I had the proportions wrong, I bought ferric chloride, AKA, ferric acid. Every board I have etched in the past has used ferric acid so I had no doubts it would work. The most effective method for using the acid is to place the board in a large vat of warmed acid which is constantly being stirred. Instead, I used a shallow bath of room-temperature acid. I was able to stir it regularly though.

Timer next to my ferric acid bath

As mentioned earlier, etching circuit boards is relatively easy, so, despite my cool, shallow acid bath, the results were spectacular. One area which had been repaired with a Sharpie was damaged and the trace was broken.

The tagger circuit board, on the right, turned out marvelously

The transistor footprint was not divided with a sharp blade on one of the two boards made that day. Fixing a problem like this is more difficult after the etching process but far from impossible. Instead of simply making a cut in thing toner, the copper had to be cut away using a blade. This took torque. Eventually the copper was cut away, even if it wasn't pretty. Just another example of recovering despite screwing up.

Divided transistor pads

The broken trace mentioned before needed repair but in this case copper was missing. To bridge this gap a short bit of wire was placed across the divide and soldered in place. Fortunately, in this case, the trace was isolated so it was no trouble to get it positioned without short anything else.

Repaired trace

With the traces in the best shape possible, a Dremel drill press and tiny bits were used to drill all the little holes for the component leads. Three different sized bits were used. The transistor leads were  small while the screw terminals were much larger. Water was spread across the board to keep dust from getting airborne.

Drill press with small bits

Some of the drilling wasn't exactly centered on the hole and some damage was done with the small holes but all of the components should be able to be mounted and soldered in place. The soldering job on the problematic areas may be more difficult than commercial boards but at this point the importance of these boards is to test the circuit before ordering professionally made boards.

Drilled boards

Discovering the improper transistor footprint was a big problem and it was addressed by the next iteration of the board. Thicker traces were also used since it was a simple matter of increasing the width before running the autorouter.

A new revision with thicker traces

After the second major revision, a third revision was made. This one had the Arduino turned 90 degrees and allowed for a much shorter board. The previous version was shortened enough to fit two copies on a 50mm x 150mm (2" x 4") board. The third version was shortened as much as possible since the cost of having boards fabricated is based on area.

Circuit layout, board view, and B/W copper traces

On a completely different subject, one of my implants had to be removed. It was not pleasant or painless. The experimental coating failed and eventually lead to a lot of tissue surrounding the offensive metal in my finger. The bulge seen below is from the protective tissue. For the gruesome pictures of the extracted magnet and tissue see the actual post.

Bulging finger


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