Is there a rule of thumb governing the choice of logic chips/discreet components or microprocessor? I have a number of intro to electronics books but none seem to address this question.

 

Is there a rule of thumb governing the choice of logic chips/discreet components or microprocessor? I have a number of intro to electronics books but none seem to address this question.

Such a choice is heavily dependent on what the circuit is intended to accomplish.

hgmjr

 

dedicated logic is faster ( generally ) but can get complicated for complicated logic. a uc is much more flexible given a limit of a few chips. ( all more or less )

 

There are so many factors - usually speed, size and cost. Other factors can be power consumption, expandibility, reprogrammability etc. One main use of descrete is also because it will allow for a much large range of input signal, protection against overvoltages etc. etc.

Speed can often mean you have to use descrete logic chips. For example it might be very hard to find processor that can do 100mhz+ that is only a one square centimeter and is cheap.

Once you have to many descrete components it usually becomes cheaper to use a programmable logic device. I often find that the cheapest/faster for many things is to use latches/shift registers connected to a cheap tiny processor. So the processor might only have 8 or so I/O lines but you can use shift registers and latches to get at tonnes of digital inputs.

 

In the consumer electronic industry the rule of thumb is cost But this do not always apply to hobbyist projects. If your hobby project cost a few $ extra it will not hurt you