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I was watching some videos on building an 8-bit computer and plan to do so myself, however, I wondered if it was possible to make something like an EPROM or 555 timers from scratch using basic electronic components?

P.S. I am relatively new to electronics, so I'm sorry if this is a dumb question

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    \$\begingroup\$ 555 timer can be built from discrete components (and it would be a good exercise). Building an EPROM from discrete components doesn't make sense to me. \$\endgroup\$
    – misk94555
    Apr 19, 2023 at 20:38
  • \$\begingroup\$ It is possible to build a wheel oneself. It is impossible to build an infrastructure for production and use of wheeled vehicles all by oneself. Be sure to have goals formed (and kept record of) before investing a significant amount of time. A 555 may be instructive, a sizeable PROM boring, the exact mechanisms of EPROMs - well - ambitious. \$\endgroup\$
    – greybeard
    Apr 19, 2023 at 20:41
  • \$\begingroup\$ understood! thanks. just for my learning, as to how an EPROM works, any schematics I could look at? was able to find some for the 555 timer and it helped \$\endgroup\$
    – 0xfffe
    Apr 19, 2023 at 20:47
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    \$\begingroup\$ You can actually purchase a kit for building a 555 from discrete components. There's even one for a complete 6502 CPU! But an EPROM depends on a special device -- the floating-gate MOSFET -- that is not available in discrete form. When building from discrete parts, a diode matrix usually serves as a ROM. \$\endgroup\$
    – Dave Tweed
    Apr 19, 2023 at 20:51
  • \$\begingroup\$ just looked up diode matrix and found this wintergroundfairlands.com/2013/10/… very helpful \$\endgroup\$
    – 0xfffe
    Apr 19, 2023 at 20:57

2 Answers 2

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You can, theoretically, build the equivalent of any IC from discrete components. (You may have to invent some yourself, like EEPROM cells...the demand for individual transistors with floating gates isn't high enough to get them into the Digi-Key catalog.) The performance will not be the same, though:

  1. Size. Naturally, your component parts will be substantially larger than their IC equivalents.

  2. Speed. Your larger components, and the longer leads used to connect them, will have substantially larger capacitances, inductances, and resistances than an IC design has to contend with. All these will contribute to reducing the operating speed of your design.

  3. EMC. Your longer wires are more effective antennas for unintended communications between devices. Self-interference is even a worse problem, despite the increased distance between circuits.

  4. Cost. A transistor from Digi-Key will cost a few cents, maybe under a cent in bulk, but individual transistors on an IC cost almost nothing.

  5. Reliability. You'd think a large device would be stronger than a small one, but metallization held nearly rigid by silicon backing is substantially more durable than macroscopic solder connections, and the square-cube law weighs heavily in favor of the smaller implementation.

So, I'd say pick your fights...hand-build a 555, but buy your EEPROMS off the shelf.

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  • \$\begingroup\$ thanks! that does make sense. any schematics for EEPROM that I could refer to know how these are built? looking up for some on google shows schematics of how it is being used as a component, but not of itself \$\endgroup\$
    – 0xfffe
    Apr 19, 2023 at 21:02
  • \$\begingroup\$ There aren't usually full schematics for EEPROMs, since they're extremely redundant. This page shows a number of representational schematics, as well as the floating gate structure that will be difficult to find in discrete components. google.com/… \$\endgroup\$ Apr 20, 2023 at 12:24
  • \$\begingroup\$ But you can make some interesting secondary memory at home - paper tape or magnetic cassette tape, maybe :) \$\endgroup\$
    – user253751
    Jul 24, 2023 at 11:55
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yes you can lookup 555 schematic diagram and you will find a ciruit to build for an eeprom i don't know but since it's an IC meaning INTRRGRATED circuit it should be possible

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    \$\begingroup\$ Can you expand your answer? \$\endgroup\$
    – Voltage Spike
    Apr 19, 2023 at 22:05

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