Since Sep 2020, it has been apparent to me that I have unconventional ideas about numerous technical topics. This includes my approach to hardware construction. I would like to share a minor innovation which is very probably unoriginal but has been hugely beneficial to my own efforts. Specifically, I have made about 20 5V tolerant, reversible LED indicator modules.
Many people are dissuaded from constructing an 8 bit computer due to cost. This includes test equipment, such as digital multi-meter, oscilloscope and logic analyzer and - for the unwary - parts and board manufacture which should cost less than USD100 can easily inflate beyond USD400. All of this is unaffordable for 1/3 of the people in one of the richest nations of the world and is probably unaffordable to more than 90% of the world population. Instead, we need more USD50 projects like
MCL65+.
I therefore intend to build a computer upwards from the chips without fancy test equipment. While I am currently able to afford a good oscilloscope, there have been occasions when this was not possible. I also have a large pile of junk which is under-utilized. I don't want to add an expensive oscilloscope to the pile when I intend to spend the majority of my time programming. My intention is to make a computer with USD50 of tools and USD50 of parts. Admittedly, I have already blown this budget with component orders which include 3000 LEDs. However, the reason for my enthusiasm should be apparent when I explain my non-innovation.
It is apparent that I require some form of test equipment to make anything complex and that I'll have to buy it or make it. I liken this task to a carpenter who shakes his head at a Black And Decker Workmate and then makes his own A-Frame. (Hence the name of the project.) In programming, there is a similar process of tool-smithing. This may be an iterative process where tools are used to make better tools which are used to complete a useful objective.
As a lazy programmer, my laziness extends to not bothering to calculate the value of a current limiting resistor for use in conjunction with an LED. Instead, I use two LEDs in series. This works best with 2.7V red LEDs. You are strongly dissuaded from using 3.3V gallium green/blue/purple/pink LEDs because the result may be dim or ineffective. (Hmmm, I wonder why 3.3V circuitry often uses blue power lights?)
In a further example of laziness, I cannot be bothered with the polarity of LEDs. I am therefore glad to confirm that it is possible to arrange two pairs of LEDs back-to-back and make a reversible indicator. This is a simplified application of Charieplexing. In this case, any two of the four LEDs glow when there is sufficient current.
In a final non-act of laziness, I have found that it is possible to get a 4*4 scrap of 0.1 inch prototyping board and insert a ring of 5mm LEDs which can then be soldered so poorly that I laughed at my own work. (Hey, I've not soldered for more than one year.) Although it is possible to arrange the same circuit on a 5*3 scrap board, the symmetry of 4*4 has better center of gravity. It also facilitates the choice of the best opposite corners to attach the fly leads. With the most symmetric board, there the most options to avoid your own soldering disasters.
As my health allowed, I spent about six hours over three separate sessions making 25 indicators. I was shocked that the first 10 worked flawlessly. This is especially true given that I laughed at the quality of my own soldering. Of the next 10, one failed to work in either orientation before one of its fly leads fell off. That was easily rectified. Of the next five, two were unsalvgeable and were discarded. (A one pin LED is particularly useless.) It is quite obvious that quality decreased as I became tired. One indicator has subsequently dimmed and this has also been discarded.
Anyhow, the result has been very worthwhile. I have 22 indicators which work like LEDs except that they work either way around, work at 5V and have longer, insulated leads which are less likely to break. When I'm working on a breadboard, I can just grab them from a pool and place them anywhere without thinking. The effort to make these indicators has already saved time elsewhere. Furthermore, this has only required about USD2 of parts and has been far more useful than a multi-meter.
The first task using the indicator lights is to make a
chain of 74HC161 binary counters. From this, it was immediately apparent that I would be using indicators almost exclusively in pairs. Therefore, my profligate use of LEDs extends to clusters of eight. The first pair of indicators was used as power lights at each end of a breadboard. This eliminates the ambiguity of the whole board being powered, especially for variants which have split power rails or no power rails. All other pairs have been used from ground to signal and from signal to power. Due to persistence of vision, logarithmic response and the varied angle of indicator lights, it is surprisingly difficult to distinguish a high frequency signal with 1/2 duty ratio from a high frequency signal with 1/16 duty ratio. However, when indicator lights are paired, it is quite trivial to determine if duty ratio is approximately half or significant deviation from half.
I highly recommend making dozens of these indicators - even if it takes you more than one day to complete the task. If you have terrible soldering due to inexperience or a long absence, it is the ideal project to get started. It is not a particularly useful project in itself. However, like a carpenter's A-Frame, it will save you time as a project progresses. I estimate that you may break even after three or four days of experimenting.
I found that it is possible to make 12 or more indicators from a 5cm*7cm prototyping board. However, it may be difficult to break a board cleanly into scraps of suitable size. My first board snapped perfectly. Possibly due to over-confidence, my second board was a disaster and this may have contributed to the latter failures. I recommend snapping the board lengthways and then repeating the process so that you have four long strips. This is the most likely process to produce 10 or more fragments with a minimum of 4*4 holes. I also recommend using general purpose tack to hold LEDs in place while soldering. This reduces the wonkiness of LEDs. It is also useful to hold the small project in place when you have molten solder.
I am so keen to share this technique that I am willing to mail examples globally at no expense. I expect all good plagiarists to be retailing indicator lights over the next two months or so. Regardless, this is your opportunity to get the original model which has already been used to bootstrap success projects. This offer is probably of most benefit to newbies without access to good test equipment. Regardless, experts may be amused by my atrocious soldering and therefore the offer is open to all. I will also include general purpose electronic components to help newbies get started. This includes 22pF capacitors, 2222A transistors and one 555 timer chip. I may also include unrelated surprise items. (I like mailing random stuff but no everyone likes surprises.) Send your details and indicate if you do *not* want the unrelated surprise items. Finally, don't spoil the surprise when you receive it!
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