AMB Laboratories DIY Audio Forums

[linux-works]

here it is, proof of concept. LCDuino thinking its a VFDuino













the last image shows what I did to connect it via the pin headers we use for the arduinos and lcds. pin3 (from the left) is missing since, on lcd's that a contrast pin - there is no contrast concept on vfd's so as a safety, I removed that pin from the header. similarly, the on right, the final 2 pins (15,16) are removed since those are for the backlight and, again, the vfd does not 'do backlight' like an lcd would. lcd's take an analog or pwm voltage for backlight but vfd's have just 4 brightness levels and they are NOT set via pins and voltages; they're set via a command protocol with 2 bits on the bottom byte being set to 1 of 4 brightness values.

if you plug in this vfd it seems to 'just plain work' as is. I have not done any testing other than a simple smoke test; and I can stay that there was no explosion when I powered things on. that's usually a good sign

I did this experiment to see how compatible this $30 vfd is. I'll continue to watch this and see how it works over time. I can't guarantee that the vfd will be a formally supported option by first-ship of the lcduino firmware but for those who want to try it, it does seem to work.

remember, there are high voltages on the back and its pretty exposed back there. there are some precautions you have to follow or be aware of - see the vfd spec sheets.

anyway, its nice to know that its at least possible with one of the special 5v compatible hitachi style VFD displays. $30 for the raw part, though (deep sigh).

[bcg27]

This might be a dumb question, but what are the advantages of the VFD over a LCD?

[amb]

This might be a dumb question, but what are the advantages of the VFD over a LCD?

The way I see them:
VFD: Brighter, more contrast (always dark background), wider viewing angle.
LCD: More background/foreground color options, more attractive characters (less pixelated), low voltage, much less current consumption.

[linux-works]

also, for same-ness matching. I have a logitech SB3 that uses a blue/green (seems more blue, to me) vfd display and if I have a vol control or dac next to it, it would be kind of nice to have it match in style and color.

with the 16x2 displays, the one I picked was the same exact size as the 'standard' lcd in 16x2. the chars are not bigger bbut they sure are brighter and more contrasty. there is no angle view issues on vfd. there -may- be some transformer singing either early on or over time as the dc/dc ages and that's a down-side. so many times the transformers whine and you 'hear' the backlight. modern led based backlights on lcd's are simple 2-4vdc and they are noise free. we'll have to see how noise free this vfd unit is.

some lcd's are transmissive color and some are transflexive; dark background or dark letters on a color background. vfd has less choice in color.

the lcd backlight is also analog and when you pwm drive it, you sort of get 100-200 levels that you can set. if you run a for-loop you can get nice fade up/down effects. that's impossible on the vfd; nothing fades on this; its 4 levels of bright based on 2 bits in a control byte.

[amb]

One thing just occurred to me -- these VFD displays have an onboard DC-DC converter to produce the needed high voltage from 5V DC, and it might radiate noise and interference. It's just conjecture at this point since I have not done any testing with them, but it's possible. The Newhaven datasheet doesn't specify what frequency the DC-DC converter operates at, but even if it's ultrasonic, it might still produce sub-harmonics in the audible band. Something to test later.

[linux-works]

definitely seems more risky for noise.

might try doing a noise test thru an a10 (rmaa) with an lcd and then another run with the vfd plugged in. if it matters, it should be visible on the tests (imho). if the graphs are pretty much the same, then I'd feel safe using it.

some people have put their lcd displays inside metal boxes. the old style lcd's had dc/dc either on them or as backpacks and the EL backlights were high voltage. so this is not a new problem for audio. it will be interesting if this is going to need special treatment or shielding or not.

the nice thing about the relay atten is that the power goign to it does not matter; control is control and audio path is audio path. even if the vfd is noisy on the dc supply, that should not get into the audio path at all.

[DorkVader]

If it's emitting electrical-field noise, won't that be "fixable" by just putting up a grounded metal plate between the VFD-unio and the rest of the amp?

This is an interesting option. While I may want to start with an LCD, the possibility of "upgrading" to a VFD is pretty cool. I really like the look of them, even though they may be more pixellated. It may be prudent to have a "dimer switch" option on a remote, or a light-sensor that auto-dims it based on ambient light. I wouldn't want a bright VFD lighting up the whole room while I listen to music at night.

[amb]

If it's emitting electrical-field noise, won't that be "fixable" by just putting up a grounded metal plate between the VFD-unio and the rest of the amp?

Maybe, but I'd have to determine if it is a problem in the first place.

This is an interesting option. While I may want to start with an LCD, the possibility of "upgrading" to a VFD is pretty cool. I really like the look of them, even though they may be more pixellated. It may be prudent to have a "dimer switch" option on a remote, or a light-sensor that auto-dims it based on ambient light. I wouldn't want a bright VFD lighting up the whole room while I listen to music at night.

A light sensor that controls display brightness is an idea that I had for the future (there is an "aux sensor" Molex connector on the LCDuino-1 which goes to an unused A/D input pin, which could be connected to a photocell), but currently there is no support for it in firmware. At any rate, as linux-works already mentioned, there are 2 bits to control the brightness on the VFD, so you only get 4 levels of brightness. With an LCD however we have much finer control of the LCD backlight, so we could make it adapt to ambient light very smoothly. No promise that this feature will ever be implemented however -- it's low on the wishlist because what we have now is pretty good already. We may find some other more important use for that input.

The current firmware lets you toggle between three display modes with the remote:

1. Normally low brightness, but if you do anything (e.g., use the remote, press the power button, or turn the volume knob), the display goes bright. After a few seconds of inactivity the display smoothly fades back to low brightness again.
2. Display is always bright
3. Display is always dark (backlight off)

The "bright" and "low brightness" levels are each adjustable via the remote as well.
Can't do this with the VFD, though.

[Shaman]

Good stuff guys!
Let us know when you get round to looking into the potential noise problems of VFDs.

On one of my projects the VFD will be in the "dirty" (power supply) chassis so I don't mind much, but in the case of my a20 preamp everything (except the transformers) will go into one box. I plan on using a piece of metal to separate PSU-LCDuino and stuff from the audio circuits but still...

[linux-works]

there it is, in its first test install. I removed an older lcd, simply plugged in this vfd (with no software changes at all; I did not bother to update any code at all on this unit) and powered it up. it said hello and the functions work (motor pot, IR remote, relays click, etc). have not tested it via audio yet but so far, it looks hopeful.

the vfd is not mounted, its just sitting there on the box floor and the wire tension holds it in place while I take photos of it. the sandwich is screwed together - but just not TO the front panel, yet. I'll get a thin layer of smoked plexi when the store is open and then reconnect it all again.

this demo box was setup with a delta-1 meant for subwoofer control. I picked 0.1dB steps and 8 relays. that gives 25.5dB range, which is more than you need for a slaved subwoofer and the .1db spacing gives quite a lot of fine control.

that motor pot was a strange surplus thing that had 2 audio tracks and 2 linear tracks along with the motor. its alps brand and its really deep so it steals a lot of the box space. but, it had at least 1 linear track and a motor and so it met the goal

the small hole to the right of the display is the IR input area. the large bulgin is the single 'config button' to mute, turn off, turn on and sometimes select in/out.

this is powered by an s25 that is fed by an AC wallwart, 9v at 1A. its not powered by usb; not sure I trust that quite yet.

so, a direct drop-in is possible, at least at the functional level.