24 January 2009

Seven-Segment Vacuum Fluorescent Display (VFD)

Do you ever go to surplus electronic stores just to wander the aisles? Years back, I used to go to Skycraft Electronics in Winter Park. It's still there. On pilgrimages back to the homeland, I occasionally will stop by but it's not the same. Back then I'd go alone or with a fellow geek and be able to spend hours digging around. Now days I have a wife and/or kids in tow that have zero patience and it's rush rush rush. It seems that the beach, Disney, or Universal is more important to them than junk heaven. They need priority adjustments.

My current area had a junkier place called Misener Electronics, formerly Pembleton Electronics, that has potential but they keep moving locations and they may be gone for good. Current rumour is that they moved from the Volleyball Courts to 500 Coombs Street. No one answers the phone and I drove by the empty looking building today. I think we've lost the only electronic junk store in town.

When Misener was open last year, I found a box of an interesting FIP (Fluorescent Indicator Panel or Vacuum Fluorescent Display (VFD)) for about 25¢ each. I grabbed a handful and added to my junk pile. These look pretty nice but what can I do with 'em? Any idea how to drive them? I started Googling the part number and few a limited number of hits. Part number NEC FIP6C15A at least reveals these specs but doesn't give any pinouts.

NEC Electronics FIP6C15A
Seven-Segment Vacuum Fluorescent Display - 7-Segment Numeric
Package Style (Basic)=SIP
Number of Digits=6
Character Height (mm)=15
Vsup Nom.(V) Supply Voltage=3.7
Iseg (A) Segment Forward Cur.=150m
Lv Typ.(fL) Luminance=700

BTW, I also found a nice description of VFDs at http://hem.passagen.se/communication/vfd.html which is where I grabbed that image of the "Expoded" (sp) VFD. Seems that a common source of VFDs is old VCR displays.

Using the ATX PSU that I put in test mode, I applied +3.3VDC across the filaments (on this VFD, the two out side pins that I labeled as Element for some dumb reason), and then randomly picked a grid (which is one of the leads not below one of the yellow blocks on the back) and stuck +12VDC on it. Then applied +12VDC to various segments which are the pins below the yellow blocks.

The result was that many segments lit depending on the combination of the grid a segment(s) I had powered. Pretty cool. I called over to my son Will who then made it his life's work to light as many segments as possible. During his investigation, he shorted a segment to the filament and we got a nice spark show and the PSU shutdown. I was worried that we blew out the VFD but after a brief power cycle, the fun returned.

This was pretty cool but obvious that it would be tough to control this with an Arduino to make it a useful display. A Maxim's Application Note 1154 lists VFD Tube Manufacturers' Web Sites. In that appnote is a list of Maxim tube driver chips that would be great for interfacing to my VFD. The MAX6934 looks about right.

Of course after tiring with the NEC VFD, we then had to rip a more complex one out of an abandoned VCR in the garage. This one (no pictures) was odd. After hooking up the filaments to +3.3VDC, any other pin that we put +12VDC on caused stuff to light. On the NEC FIP6C15A VFD, the grid had to be powered separately, then segments were lit by putting power to pins. This VCR VFD seemed skip the grid power need. ?? Doesn't seem right but that's what it was doing.

20 January 2009

PC Power Supply for the Lab Bench

Seems like everyone has converted an old PC Power Supply for use in the lab. I've been using old wall warts for most of what I need so I haven't really paid much attention to the weekly instructable or hack that gives the step-by-steps. I admit, it sounds great. Plug in the supply and you have instant regulated +3.3VDC, +5VDC, +12VDC, -12VDC, -5VDC, and +5VSB. Yup, sounds great.

Wait. +5VSB, what's that? It's the 5 Volt Standby voltage. It's the voltage that remains running when the power supply suspends and is used to power the "wake on" devices such as network cards and modems used to bring the computers out of suspend mode. It's been around on PSUs for quite some time, I guess just haven't noticed it.

Since the wall warts are ok for me, why am I writing about a PSU? Because Spoofee told me about a dirt cheap one. Buy it, rebate, and it's almost free! I love almost free 'cause it's really cheap. Okay, I did the buy and rebate thing and now have a PSU sitting on the bench. I guess the instructables are needed.

But first a warning. All I'm doing here is simply putting the PSU into a test mode so I can vampire the juice from a connector. Although the volts are regulated, the current can zap the crap out of your circuit if you short something. Check out the instructable above to see how you can do this better. Read the comments to that instructable to see the many cons on using a PSU for your project. I'm lazy and just want quick power to run a VFD that I'll blog about soon. You, are not lazy and will do this better. If you do this to a PSU, be careful.

Here's a real decent pin-out that I found at Help With PCs. I especially like the color coding 'cause it helps my old eye find the right volt pin quickly.

The Ultra X-Connect PSU that I have has a ATX 2-pin, 6-pin Xeon, 4-pin Pentium 4, and five 4-pin Molex connectors.

A problem with ATX PSUs, they won't power up without the Main Power connector being hooked up. To power up an ATX or ATX-2 PSU for testing, short pin 14 (PS_ON) with one of the grounds.

I just stuck a wire in the 20-pin main power connector and shorted pin 14 (PS_ON) to pin 15 (GND). Just like that pic over on the right.

The PSU rumbled to a start and viola, free power. VFD, here I come.