12 Nov
2022
12 Nov
'22
5:41 p.m.
On Sat, Nov 12, 2022 at 12:18 PM Chuck Guzis via cctalk
<cctalk(a)classiccmp.org> wrote:
On 11/12/22 02:28, Tony Duell via cctalk wrote:
Yes, that, plus since many products have a hardware team and a
firmware/software team, the hardware can be designed to general
requirements and sent out for manufacture while the software team has
time to write the firmware (and make changes long after the hardware
is set).
One of the first times I encountered this was stripping some old
emergency exit lights for parts c. 2008. The switching supply had an
8-pin PIC for the oscillator instead of a 555. Yes, a 555 could have
done it, but the PIC didn't need any external components to set the
frequency, components that can drift with age, and components that
take up board space. Even if the 555 and MCU were identical in cost
for the IC, the MCU was cheaper because of the smaller footprint.
Additionally, the designers had some flexibility. To change the
frequency with a 555 after manufacture is an expensive proposition.
With an MCU, if it's flashable in-circuit (clip or possibly
programming pads near/at the MCU), then one can change the behavior
without melting any metal or purchasing components. While one may
never need to change the frequency of a SMPSU oscillator after initial
design, there are plenty of products where it's handy that the
hardware guys can say "here's an output that can go from 1/10Hz to
20Khz - what do you want it to be?" and not worry about design
limitations, just set the frequency in the firmware and it does that.
You can build some generic hardware (X inputs, Y outputs with Z mA
current drive) and fine tune things later, or have variations on what
the inputs mean and not have to change the PCB.
Yeah, the 555 is extremely simple and is well known and is fairly
cheap, simple MCUs are simple (and cheap) even if they aren't 100%
deterministic like a chip with 20-30 transistors. There's economic
advantage in flexibility.
-ethan
... This is the sort of
thing I'd do with a couple of transistors or an NE555 depending on
which turned up in the junk box first.
One thing that a small MCU has over a 555 is that it can be programmed
once and you can be assured of its frequency stability. No fooling with
pots and caps to get the thing to work the way you'd like.