I absolutely agree you get a better design following guide lines in the data sheet. I just would not limit the design to the suggestions in the data sheet and text book.
My LED flashlight, and probably yours also, works just fine with battery and LEDs. No resistors needed.
Good theory suggests not charging batteries in series, but every rechargeable battery pack does so.
The data sheet for TTL chips may say 4.75 to 5.25 V for VCC. Of course we can run them at voltages outside these suggestions but performance may vary outside the specs on the data sheet. Most work just fine at 4.5 or 6 V. You may even get some to operate at 9 V, but I would not market such a product.
Filter caps on battery powered circuits? Well, I have omitted them on occasion, but again ... I would not put such a product on the market without them.
Suggested current for an LED may say 20 mA. That doesn't mean you MUST drive them at 20 mA. If you don't need full brightness they may work just fine at 5 or even 1 mA. You can drive an LED from a CMOS logic chip/ I just would not try to drive other logic gates from that same output.
Drive an LED, cathode to ground, from a TTL gate or op amp? Sure. use the current limiting high side driver as the ballast resistor.
Drive an LED from TTL, anode to VCC through a resistor, and still use it to drive other logic gates? Sure, just keep the current down to a few mA and use a parallel resistor to give a good high out.
My LED flashlight, and probably yours also, works just fine with battery and LEDs. No resistors needed.
Good theory suggests not charging batteries in series, but every rechargeable battery pack does so.
The data sheet for TTL chips may say 4.75 to 5.25 V for VCC. Of course we can run them at voltages outside these suggestions but performance may vary outside the specs on the data sheet. Most work just fine at 4.5 or 6 V. You may even get some to operate at 9 V, but I would not market such a product.
Filter caps on battery powered circuits? Well, I have omitted them on occasion, but again ... I would not put such a product on the market without them.
Suggested current for an LED may say 20 mA. That doesn't mean you MUST drive them at 20 mA. If you don't need full brightness they may work just fine at 5 or even 1 mA. You can drive an LED from a CMOS logic chip/ I just would not try to drive other logic gates from that same output.
Drive an LED, cathode to ground, from a TTL gate or op amp? Sure. use the current limiting high side driver as the ballast resistor.
Drive an LED from TTL, anode to VCC through a resistor, and still use it to drive other logic gates? Sure, just keep the current down to a few mA and use a parallel resistor to give a good high out.