18 Jun
2013
18 Jun
'13
11:16 a.m.
A functional USB interface can be done in an 8 pin
microcontroller that
probably costs an order of magnitude less than the sockets used in your
20 MSI package implementation.
Since when has cost had anything to do with complexity?
And if that's an 8 pin microcontroller, then if you use 2 pins for power,
and 2 pins for the USB signals, you only have 4 pins left to tlak to
wahtever. Which probably implies a serial interface on that side too. So
more circuitry is needed to link that to whatever yoy are working with.
It appears that you measure complexity by the number of devices you
solder to the PCB, or perhpas the total number of soldered joints. I do
not. I consider things like the number of active devices (or gates, or
whatever) inside the ICs, the number of states of state machines, etc.
let me ask you a simple quesiton. You have to flash an LED at about 1Hz
-- the exact frequency is not important. Nor is the duty cycle (within
reason). You also have a suitable supply line (so no need to consider 3
terminal regualtors, etc)
Now, off the top of my head there are 3 obvious solutions (there are many
more too, of course ) :
A discrete component multivibrator -- 2 transsitors, 4 resistors, 2
capacitors, LED
A 555 astable --555 Timer IC, 3 resistors, 1 capacitor (2 if you are a
purist and want to decouple 'control voltage), LED
An 8 pin microcotnroller, 1 resistor, LED
Which of those 2 you consider to be the simplest?
232C and USB are both bit serial, but USB has higher speeds, friendly
voltage levels, power from a host included and well-defined protocol.
Actually, the 'friendly votlage levels' could be a minus-point in that it
is likely a USB interface conenctor is connected directly to some large
and complex IC, while an RS232 port will almost certainly invlove a
simple buffer IC or two. So that if you accidentally connect too high a
voltage to the cable, in the case of USB you have a lot of work to do, in
the case of RS232 it's one cheap IC that will take a few minutes to
replace (even if soldered in).
And the USB protocol is significantly more complex than RS232 and that to
me is a major disadvantage _where the extra capabiliities of USB are not
needed__. As an interface to large-ish remveable memory devices it seems
fine. As am interface to a fairly low-speed ADC system it seems ridiculous.
-tony