Curiosity killed my clock oscillator :)

[[email protected]]

I'm more of a hobbyist than a hardcore electronics whiz, so I figured
I'd ask someone with more knowledge than I. In my spare time, I'm
building a hydroponics system that's interfaced with my PC using a
pic18f4550. Most of the hardware is finished, and I've already got a
Visual C++ program and some PHP scripts that take care of all of my
software needs. My only problem is the external oscillator I'm using
for the pic. I mistakenly ordered a 3.3V clock oscillator, while
everything else is operating off of a hacked PC power supply
generating 5.0V. The oscillator is 16Mhz, and I'm using PLL to run
the pic at 48Mhz. I went ahead and stuck the oscillator in b/c I
didn't feel like spending more money. It worked well for a month or
two, but now it's acting pretty flaky and the pic freezes up
randomly. So... that being said, my question to you is: What are the
consquences of running a clock oscillator like this, at 5.0V when it's
only rated for 3.3V? There's the obvious risk of ruining it, but I'm
curious as to whether the voltage alters the frequency or output
waveform at all. Mainly, I'm worried that I may have to swap out my
18f4550 now.

Thanks,
Aaron

 

[[email protected]]

I'm just using it b/c that's what was on some of my old schematics.
I'm not worried about power comsumption or anything - I've got 15A
available from my power supply, and I'm only using ~600mA. I did
order a crystal to replace the oscillator though, so my problems
should clear up, I hope. Thanks for the info guys.

Aaron

 

[Michael Black]

Running a power supply at such a small percentage of it's design power is
pretty inefficient. You can run something like that more efficiently with
just a 5V SMPS designed for cell phone or other 5V power sources, have a
smaller footprint, and use the PC power supply for something more demanding
to boot!

At my office, we've accumulated a number of 5V, 12V, and 5V/12V switchers
from various devices which either died or got used with POE instead, and
they're incredibly handy for small electronics projects. They're never as
close to 5V or 12V as you get from a PC power supply, but still within the
specs of all 5V or 12V gear I've seen... say, within a quarter volt.

I'll second that.

Too often we see people asking about how to use a "computer power supply"
as a bench supply, and then they have to load it down because they have
no need for the high current the supply outputs.

Most of the computer supplies I've brought home after finding them
waiting for the garbage truck have been scrapped, I pull out boards
(and strip off the parts) and then use the cases for project boxes.
At the very least, they make great boxes for analog power supplies,
using transformers I've pulled out of some other piece of electronic
junk.

The beginner doesn't even realize that there is a world of switching
supplies out there that aren't "computer power supplies". I've gotten
surplus switchers that are far more appropriate for average use, since
they are smaller and put out more reasonable current levels.

And yes, other scrap electronics is a good source of lower current
switching supplies. VCRs increasingly have switching supplies, though
they tend to be part of the main circuit board (so it's less easy
to extract the power supply). Inkjet printers are a great source
of lower current switching supplies, not only are they lower current
but they tend to be built as a separate board and may even be in their
own casing. Plus, you can get all the inkjet printers you could
possibly want, just waiting for the garbage trucks.

When I needed a 24v supply to run a laptop, I took apart the first inkjet
printer I put my hands on, and there was a nice 24v supply of the needed
current capacity. Just when I was about to build up an analog supply.

Michael

 

[[email protected]]

Hmm. I'll check out some of the junk printers, vcr's, etc. that I've
got lying around. I really didn't notice any problem with using the
supply I've got. I'm gonna be adding several relays to control some
24V AC valves, so I may actually end up needing a couple amps. As far
as inaccuracy, that's not too big of an issue - I think a 5V regulator
is like $1.50 at Radioshack. Thanks for the constructive criticism.

Aaron

 

[[email protected]]

The supply is actually from an elderly Mac that I scrapped out years
ago. I used it simply because it's ultra-compact, but still fairly
high output.

Aaron

 

[T]

I'll second that.

Too often we see people asking about how to use a "computer power supply"
as a bench supply, and then they have to load it down because they have
no need for the high current the supply outputs.

Most of the computer supplies I've brought home after finding them
waiting for the garbage truck have been scrapped, I pull out boards
(and strip off the parts) and then use the cases for project boxes.
At the very least, they make great boxes for analog power supplies,
using transformers I've pulled out of some other piece of electronic
junk.

The beginner doesn't even realize that there is a world of switching
supplies out there that aren't "computer power supplies". I've gotten
surplus switchers that are far more appropriate for average use, since
they are smaller and put out more reasonable current levels.

And yes, other scrap electronics is a good source of lower current
switching supplies. VCRs increasingly have switching supplies, though
they tend to be part of the main circuit board (so it's less easy
to extract the power supply). Inkjet printers are a great source
of lower current switching supplies, not only are they lower current
but they tend to be built as a separate board and may even be in their
own casing. Plus, you can get all the inkjet printers you could
possibly want, just waiting for the garbage trucks.

When I needed a 24v supply to run a laptop, I took apart the first inkjet
printer I put my hands on, and there was a nice 24v supply of the needed
current capacity. Just when I was about to build up an analog supply.

Michael

I'm happy as a clam since I finally got a power supply that puts out 5V
with a nice constant current up to 3A. It's a Delmot HY1803D, 0-18VDC at
0-3A. Right now I've got it powering two Bare Bones Boards (Arduino
Clones) and 5 LED's and it's only drawing 60ma, about what I'd expected.
It's also allowed me to experiment and find that I can run the BBB's on
2.7VDC at 20ma.

When things die around here they get checked to see if they can be
easily repaired. If not they get harvested.

 

[Don Bruder]

When things die around here they get checked to see if they can be
easily repaired. If not they get harvested.

<chuckle>

Thus speaks a fellow 'lectroni-geek