what few notes can u write on decimal counting assembly DCA?
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This sounds like a school homework assignment. So I will answer with some notes that are correct, and may educate or entertain readers with info about older technologies, but are not likely to be a good substitute for students paying attention in class or doing assigned readings. The breadth of the notes points out that if you want a good answer to your question, it helps to state the question more specifically. Including details that can help limit the scope of the question will make it more likely that you get useful and relevant answers. This is true whatever you are asking about.
But first, to answer Boss, a Decimal Counting Assembly can refer to any of a wide variety of mechanical, electromechanical, or electronic assemblies capable of counting, with output available in decimal format (either displayed or activating one of n lines). They may be single or multiple decade. The term is so generic I can think of hundreds of different version and applications you can find them in - though they might not be called that.
Choosing a suitable DCA involves knowing the application for which you will be using the DCA.
Some application requirements to consider:
What is the maximum counting speed needed? This will determine whether a mechanical solution is workable, or a purely electronic one is required.
Is audible indication that counting is taking place required? If so, mechanical DCAs may more than satisfy the requirement with no addition parts or speaker needed.
Is visible display of the current result required? If so, what are the viewing conditions? (These include viewer distance, ambient light level, and whether it is being viewed directly or recorded on film or video. Some display methods use multiplexing, which can result in incorrect values being perceived if recorded at film/video rates incompatible or unsynchronized with the multiplexing rate.)
Does the result need to be non-volatile (maintained without power)?
Most of the mechanical solutions inherently provide this capability.
It can be provided on some electronic DCAs as well, though if the DCA is to display the result, you need to be careful about selecting a type of display that is also nonvolatile. (Think e-paper.)
Is unidirectional counting sufficient, or is bidirectional counting needed?
(Your first answer to the question might miss some thinking-outside-the-box opportunities. I designed a pinball machine with a bidirectional one in 1974, that instead of halting further counting when "tilted", simply reversed the direction of counting. The longer you kept your ball in play after tilting, the more you worsened your score.)
Is reset-to-zero ability required and/or prohibited?
What should happen if asked to increment when already at maximum count (or decrement when at zero)?
How many decades (full or partial) are needed?
Do you need only decimal assemblies, or do you need duodecimal as well?
What power source is available?
What endurance is required?
What resistance to physical shock is required?
What are size/space constraints?
Are outputs comparing the result to fixed or user-adjustable limit values required?
Is tamper detection required?
What are the specifications (ie, volt, current, pulse width) of the input signal to be counted?
Is gating of an internal oscillator needed?
What connectors (or mechanical or optical interfaces) will be used for input (and if applicable, output) signals?
Should the result display and/or entire assembly have a steam-punk look to it?
For some related interesting vintage techniques, see http://www.one-electron.com/Archives/Tube/Signalite/Signalite_Vol3_No3.pdf.