My nose in the books during y’day’s rainstorm found me reading up on 7-segment displays. That is our trivia for today. These are those neat tubes that showed numbers, and when you looked into the tube you could see they were 3-D. They were the precursors of flat 7-segment LEDs. Remember those 1975 Casio wristwatches you had to press the button to see the time? That’s what I mean.
I had a 1976 calculator with a tube 7-segment display, the one you turned it upside down to spell various words like 07734 for “hELLO”. It used a set of batteries every four days even when turned off. I believe it needed six volts to operate. Rusty laughed when I spent $40 on it but we later planned nine years of our investments with that gadget. Proving again, it is not the calculator, but the man behind it, that really counts.
I discovered the workings, that the display requires an integrated circuit to input a 4 digit binary number which gets translated into a 7-segment display. As luck would have it, there was one (shown here) in my toolbox. Thanks to my studies with LEDs, a different technology, I was able to see the chip was upside-down in the package and I knew exactly the significance of “common cathode”.
I also discovered the digital readout on many gas price signs is a 7-segment display because LCDs themselves are too fragile for outdoor temperature changes. That’s the gas signs guys, known as a “totem”, and not the gas pumps. Notice the display is slanted slightly to the right. There is a reason for that, too. If becoming a mad scientist is fun, how come I have to work so hard at it?
I believe I have the knowledge to unintegrate the circuit, that is, to get this thing to display without resorting to a factory-made chip. What an accomplishment that would be (for me)! Let me check my records, hang on. Back. The lamp cost $1.99 making it far cheaper than a LCD, but still expensive enough that I will calculate the voltage from the Arduino pins, something I have avoided before. Don’t even ask me how to display a two-digit number at this point. It is now 6:50 AM.
Less than two hours later, I report complete success. Please read the meeting minutes for details. Using only components in my tool kit and planning the entire Arduino code on the fly (as I typed it in), I got the entire setup of code, brainboard, breadboard and components to work the first time. The only snag was it took me a few minutes to realize I needed two delays between the flashing digits rather than one. Well, because if it doesn’t flash, how do you really know it is working? Congratulations if you can figure out why.
In celebration of this landmark achievement, I’m spending the rest of the day in the library. But not to get carried away, I still do not have any practice or good methods of wiring circuits permanently. That is an area I will eventually need to concentrate on, which probably means learning to etch printed circuit boards.
Wait, there’s more. Didn’t I mention sewing? I signed up for a $35 sewing course. It’s a basic “how to” on a machine, since I have no intention of learning to sew by hand. This type of skill is, in my opinion, going to be important soon, although it has not been worth much over the past 40 years. But today, it does not make sense to pay $18 to get a cuff put on a $4 pair of thrift store trousers.
I have three goals with sewing, and I’m not likely to forget typing class, where I was the only man in a room full of single women. That was a long time ago, but man that was a fun class and for six months afterward. I want to cuff my own pants, I want to make all my shirts short-sleeve, and I want every t-shirt I own to have a “tit” pocket that fits a DVD. These are noble causes, and you’d agree if you ever made the mistake of wearing a long-sleeve shirt in Florida. I have a right to bare arms.
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