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USB function generators?

J

Joerg

Jan 1, 1970
0
Gents,

Unless it rains on Sunday and I have some time I might just junk this
dreaded Wavetek Model 23 generator. Looked around for USB-based
generators and found a nice li'l scope/gen combo:

http://www.allspectrum.com/store/product_info.php?products_id=2778

Not a lot of info, seems it has no galvanic isolation from the computer
like some others <knuckles turning white ...>. However, unlike many
others it does go down to 5 millihertz so can be used in machine, stress
and vibration testing which I need to do at times.

What do thee think?
 
N

Nico Coesel

Jan 1, 1970
0
Joerg said:
Gents,

Unless it rains on Sunday and I have some time I might just junk this
dreaded Wavetek Model 23 generator. Looked around for USB-based
generators and found a nice li'l scope/gen combo:

http://www.allspectrum.com/store/product_info.php?products_id=2778

Not a lot of info, seems it has no galvanic isolation from the computer
like some others <knuckles turning white ...>. However, unlike many
others it does go down to 5 millihertz so can be used in machine, stress
and vibration testing which I need to do at times.

What do thee think?

USB isolators are probably not expensive.
 
J

Joerg

Jan 1, 1970
0
Nico said:
USB isolators are probably not expensive.

In this case it would be a bit more challenging because the thing is
also supplied via the USB jack. I could fix that, but ideally I'd like
something I can plug in and it just works.
 
M

Martin Riddle

Jan 1, 1970
0
Joerg said:
That could work, if it's happy with 400mA. Unfortunately a lot of
stuff these days exceeds even the max load of 500mA, in particular
disk drives.

I couldn’t say if it actually sources 400ma since our USB devices have
their own power source.

On another note, My laptop's USB port cannot supply power to 2 2.5"
drives at once, nasty head movement occurs.

Cheers
 
J

Joerg

Jan 1, 1970
0
Martin said:
I couldn’t say if it actually sources 400ma since our USB devices have
their own power source.

I think that's what the Keterex datasheet says.

On another note, My laptop's USB port cannot supply power to 2 2.5"
drives at once, nasty head movement occurs.

Well, that's the other problem. I've usually already got some lab stuff
hanging on the laptop and while this is a ruggedized computer there will
be a limit. The Velleman datasheet isn't exactly forthcoming with data
like that.
 
J

Joe G \(Home\)

Jan 1, 1970
0
Analog devices have a USB isolator IC, but you still need power isolation.

Joe
 
M

Martin Riddle

Jan 1, 1970
0
Joe G (Home) said:
Analog devices have a USB isolator IC, but you still need power
isolation.

Joe

That’s what is in the Keterex box.

Cheers
 
N

Nico Coesel

Jan 1, 1970
0
USB is always a driver hassle. I try to buy USB devices that also work
in Linux, so if the company goes bust, you can at least run the box
under linux.

$300 would get you a nice function generator at a ham swap meet. My
PM5191 was $125 in a freakin' store (RA Surplus, now defunct) years
ago. You can't get much money for low bandwidth generators these days.

Well... a good HP3314A still sells for a couple of hundred. More
recent Agilent generators fetch even more. AFAIK those are USB and/or
ethernet controllable.
 
N

Nico Coesel

Jan 1, 1970
0
Joerg said:
I think that's what the Keterex datasheet says.



Well, that's the other problem. I've usually already got some lab stuff
hanging on the laptop and while this is a ruggedized computer there will
be a limit. The Velleman datasheet isn't exactly forthcoming with data
like that.

If its from Velleman I'd stay away from it. They also sell kits. You
can download the schematics from their website. The designs are far
from brilliant and kits that are intended to be connected to the mains
only meet the PCB design rules minimum clearance.
 
J

Joerg

Jan 1, 1970
0
Nico said:
If its from Velleman I'd stay away from it. They also sell kits. You
can download the schematics from their website. The designs are far
from brilliant and kits that are intended to be connected to the mains
only meet the PCB design rules minimum clearance.

Yes, it is from Velleman.
 
P

Paul Keinanen

Jan 1, 1970
0
In this case it would be a bit more challenging because the thing is
also supplied via the USB jack. I could fix that, but ideally I'd like
something I can plug in and it just works.

Indeed, the USB isolator and a self powered USB hub would be quite
nasty.

Perhaps a miniature laptop with big batteries could be floated with
the test equipment, but the stray capacitances could cause problems.

Doing measurements with the test system floating on the mains voltage
would also be dangerous.
 
J

Joerg

Jan 1, 1970
0
Paul said:
Indeed, the USB isolator and a self powered USB hub would be quite
nasty.

Another challenge in many of my jobs is the EMI that some of these
converters kick out.

Perhaps a miniature laptop with big batteries could be floated with
the test equipment, but the stray capacitances could cause problems.

Doing measurements with the test system floating on the mains voltage
would also be dangerous.

In that respect I am quite brazen but I make sure nobody gets too close
to my lab bench while this stuff is running :)
 
J

Joerg

Jan 1, 1970
0
The HP3314A has a control panel, so it's not like you are buying a
black box USB device from a Chinese company that won't exist in a few
years. Black boxes can become bricks if the drivers are history. ...


How do drivers become history? With all my black boxes they came with
the box. Ok, I do not change operating systems at every whim some guys
in Redmond might publish. If a "new and improved" OS is not backwards
compatible with my legacy stuff I won't buy, I'll stay with the old OS.

... Think
about all the ISA controlled items that have become bricks. ISA GPIB
boards are valueable only for their trade in value with Nation
Instruments. Anybody need a scsi drive? Now ethernet is another story.
It doesn't need drivers.

Huh? You can buy plenty of brand new PCs with numerous ISA slots.
Regular quality or industrial stuff. And I'd venture to say that you
will find a similar selection 10 years from now.

I've seen the similar Fluke or Tek function generator that cuts out at
11Mhz go for about $200. I think Joerg's issue is a lack of local
geeks. ;-) In the bay area, these items are very common on the used
market. Probably LA as well.

Yup, out here there's abosultely nothing going on of what you have in
the Bay Area in terms of electronics stores. IOW, out here there are
none left.
 
J

Jamie

Jan 1, 1970
0
Joerg said:
Another challenge in many of my jobs is the EMI that some of these
converters kick out.

Not using potted or toroidal coils in the buck area usually causes this
and a few bypassers here and there.

Nice EMI radiator using open coils :)
 
J

Joerg

Jan 1, 1970
0
Jamie said:
Not using potted or toroidal coils in the buck area usually causes this
and a few bypassers here and there.

Nice EMI radiator using open coils :)

Potted or "shielded" inductors have a surprisingly large air gap,
camouflaged by using a potting compound in "ferrite color". A guy from
the German NG recently did a test. Soldered an LED to an inductor of
same type, held it over the other ... and there was light :)
 
J

Joerg

Jan 1, 1970
0
John said:
It's raining here, headed slowly your way.

Yup, that's why we just walked the dogs :)

Got leaks?

We had one that I diagnosed as too short chimney flashing, when rain
storms in sideways. Just like Forrest Gump said, there's sideways rain,
upside down rain, big old fat rain ...

Rain in May is unusual here. We had a very wet winter, lots of
snowpack, long hot (indoor) showers in the forecast. I hope it's a
trend.

My wife just lit a load in the wood stove. In May! Global warming ...
ROFL ...

Anyhow, two cords of wood 10 years ago, then three, now four, and next
year we'll order five because we almost ran out this time.
 
M

Martin Riddle

Jan 1, 1970
0
Joerg said:
Yup, that's why we just walked the dogs :)



We had one that I diagnosed as too short chimney flashing, when rain
storms in sideways. Just like Forrest Gump said, there's sideways
rain, upside down rain, big old fat rain ...



My wife just lit a load in the wood stove. In May! Global warming ...
ROFL ...

Anyhow, two cords of wood 10 years ago, then three, now four, and next
year we'll order five because we almost ran out this time.

Must be a trend. I've see quite a few front yards here where wood has
been delivered.
Big unsplit logs. Looks like a lot of work, they must be more than 3
cords each.

Cheers
 
J

Joerg

Jan 1, 1970
0
Martin said:
Must be a trend. I've see quite a few front yards here where wood has
been delivered.
Big unsplit logs. Looks like a lot of work, they must be more than 3
cords each.

Well, it's _hugely_ less expensive than heating with propane or electric
heat pumps.
 
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