VFD and Audio

E

EEng

Guest
Has anyone used a VFD in audio/RF circuitry? Have you noticed any
noise problems? I'm wondering if the controllers charge pump to
create the VFD rails (internal DC-AC conversion) has created any
picket fencing or other noise problems.

I'm using the MAX6850 from Maxim to drive a 12 character VFD
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=3636

My alternative is to go with 14seg LEDs and the MAX6954
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=3410

If it did produce noise for you, was shielding enough to eliminate it?
I'd really like to use VFD instead of LED but the circuit 2" behind
the display is all audio processing in the human voice ranges and DTMF
encoding. LCD is not an option due to harsh outdoor environment and
sunlight.
 
"EEng" <unmaileeng@budget.net> wrote in message
news:gugib0tr6u7ggt88qqvmeup1i89qmjsrct@4ax.com...
Has anyone used a VFD in audio/RF circuitry? Have you noticed any
noise problems? I'm wondering if the controllers charge pump to
create the VFD rails (internal DC-AC conversion) has created any
picket fencing or other noise problems.
Click to expand...
Charge pump?? You need a small smps for this. Even small VFDs end up eating
about 2.5W.

Short version, no. I wouldn't expect problems like this, but I would be
careful about making this a subsystem, with it's ground and power paths
separated from the audio part of the system.

The audio system also should always be designed with high rejection of noise
on the supply rails.
Check your op-amp specs carefully, some have good PSRR in audio frequencies,
but absolutely lousy up in the 100-500kHz band.

Proper supply bypassing, and PCB layout will go a long way to making this a
non-problem.
 
On Sat, 29 May 2004 19:22:43 -0700, the renowned EEng
<unmaileeng@budget.net> wrote:

Has anyone used a VFD in audio/RF circuitry? Have you noticed any
noise problems? I'm wondering if the controllers charge pump to
create the VFD rails (internal DC-AC conversion) has created any
picket fencing or other noise problems.

I'm using the MAX6850 from Maxim to drive a 12 character VFD
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=3636

My alternative is to go with 14seg LEDs and the MAX6954
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=3410

If it did produce noise for you, was shielding enough to eliminate it?
I'd really like to use VFD instead of LED but the circuit 2" behind
the display is all audio processing in the human voice ranges and DTMF
encoding. LCD is not an option due to harsh outdoor environment and
sunlight.
Click to expand...
Have you considered an organic LED character display? Very wholesome..

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
On Sat, 29 May 2004 19:22:43 -0700, EEng <unmaileeng@budget.net>
wrote:

Has anyone used a VFD in audio/RF circuitry? Have you noticed any
noise problems? I'm wondering if the controllers charge pump to
create the VFD rails (internal DC-AC conversion) has created any
picket fencing or other noise problems.

I'm using the MAX6850 from Maxim to drive a 12 character VFD
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=3636

My alternative is to go with 14seg LEDs and the MAX6954
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=3410

If it did produce noise for you, was shielding enough to eliminate it?
I'd really like to use VFD instead of LED but the circuit 2" behind
the display is all audio processing in the human voice ranges and DTMF
encoding. LCD is not an option due to harsh outdoor environment and
sunlight.
Click to expand...

The Agilent 34401A DVM - at least the one I have - has a huge bunch of
spikes that come *out* the input terminals from the VFD drivers. They
cleverly software-zapped low AC measurement levels to hide the
resulting background. The kickout has been enough to disturb some
low-level circuits being measured.

I use VFDs in most of my instruments that have displays, some of them
120-dB range analog thingies. Noritake mostly, some 4x20 intelligent
dot-matrix modules, some bare 8-char 16-segment tubes, software
scanned. But you need to take reasonable care to keep the HV supply
and the VF drivers away from any sensitive analog stuff. Mechanical
shielding isn't likely to be needed, although planning for a flat
electrostatic shield (sheet of aluminum maybe) if the geometry forces
low-level things close to the VF or its drivers.

The VFs seem absolutely reliable as long as you don't plain break
them. We've seen no segment dimming problems in units that have been
running for 10 years.

John
 
EEng <unmaileeng@budget.net> wrote:

Has anyone used a VFD in audio/RF circuitry? Have you noticed any
noise problems? I'm wondering if the controllers charge pump to
create the VFD rails (internal DC-AC conversion) has created any
picket fencing or other noise problems.

If it did produce noise for you, was shielding enough to eliminate it?
I'd really like to use VFD instead of LED but the circuit 2" behind
the display is all audio processing in the human voice ranges and DTMF
encoding. LCD is not an option due to harsh outdoor environment and
sunlight.
Click to expand...
A lot of car-radio manufacturors solve this problem by having the VFD
converter in a separate lump attached to the radio.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
 
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