Author Topic: Vacuum fluorescent display to clock display  (Read 50158 times)

0 Members and 1 Guest are viewing this topic.

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #100 on: September 29, 2016, 10:33:33 pm »
Can you find a 74LS164 and two 74LS395 chips?  We can use them to build a fake '595 style shift register.   See attached schematic.   Ignore all /Qn pins.  The top '395's Q0-Q3 pins are equivalent to '595 Q4-Q7.   If you need to daisychain take the output from the '164 Q7 pin.  The functionality is identical to the genuine 74xx595 apart from /OE which we don't need and haven't implemented.

If not, lets get going with a string of 4013 D type flipflops then.  It wont give us the simultaneous outputs updated by a separate latch pin that a '595 would (unless we double up on the D types and add a parallel latch) but will get you happy sending bytes out of the Arduino SPI style.

I took a look at the Sparkfun link + the onwards link to billdr, and although they're good on the hardware side of things, they are bitbanging the data transfer.  The AVR on the Arduino has a SPI peripheral, the eventual aim is to be busily updating a lot of VFD digits while running a clock in realtime without loosing any ticks, so relatively slow bitbanging is a crutch you need to discard as soon as you know the '595 is hooked up correctly and working.

Take a look at http://www.appelsiini.net/2012/driving-595-shift-registers.
« Last Edit: September 30, 2016, 03:54:46 am by Ian.M »
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #101 on: September 30, 2016, 09:08:35 am »
i wont guarantee i dont have them, i might finish this then find them for all i know the boards are anarchy little bit of everything everywhere, but i dont remember seeing them.
in case your wondering how i got my hands on over 200 circuit boards i went to an auction that had a guys stuff and he was a life long hoarder of anything electronic but his collection is a bit iffy when it comes to shift registers or other "specialized" ics i quote specialized because i have found ics i didn't even know existed (parity trees) but shift registers seem to be at a deficit
« Last Edit: September 30, 2016, 09:16:52 am by neo »
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #102 on: September 30, 2016, 11:13:22 am »
i just de-soldered 8 4013 D type flipflops at 2 flip flops a chip i have 12 to play with assuming 100% success rate which is non practical, one problem however is that their leads are not long enough to breadboard
« Last Edit: September 30, 2016, 10:15:55 pm by neo »
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #103 on: September 30, 2016, 11:45:23 am »
Leads too short  to breadboard?   There are only two reasonably practical options - solder them in some tripad or matrix board (gets expensive if you are just hacking around with dodgy chips) or dead-bug them. That's take a sheet of stiff card or similar and some STRONG double sided tape.  Stick each one down with its legs in the air and IMMEDIATELY write at its pin 1 end the part number.   Wire pin to pin with Kynar wire wrapping wire.  You can also use the sort of magnet wire that has solder-through enamel.  Any other type of wire is more trouble than its worth.

Chips with short leads are virtually unusable for prototyping.  You might as well not have them.  However for ONE OR TWO chips it could be worth trying to extend their pins, so see if you can find that 74LS595 and a 74LS138 (or any other logic family variant of those two part numbers)   
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #104 on: October 01, 2016, 02:47:42 am »
or i could just solder them to cheap perfboard i have lying around
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #105 on: October 02, 2016, 03:25:20 am »
OK, connect each 4013 Q output to the D input of the next flipflop in the chain.  Connect all the CP pins together.  Connect all the CD pins together and  connect a single 1K resistor for the whole chain from there to 0V.  Do the same with the SD pins. 4 chips will then give you an 8 bit shift register without a latch.  If you want it latched then you need to T off sideways from each D output of the chain via another flipflop.  All the latch flipflops are clocked together like the main chain, and apart from their D wiring should be wired like the main chain.  If you use 8 chips, you can use one half of each chip for the chain and the other for the latch.   That gets you something very similar to a '595 chip.

Meanwhile I've been digging out parts.  I have a couple of 74HC595 chips on a breadboard with some ULN2803 chips as level shifters and a HNM-05SS62T 7 segment 4 digit VFD clock display.  I need to add some NPN active pullups to get that to drive the display properly.   I've already had the VFD illuminated with 1.5V DC on the filament and 24V between the filament and the grids and anodes from a little 1W DC-DC converter module, 5V in 24V out, just to check the voltages and currents will work before I assemble the driver circuit.   I'm forgoing my usual choice of a Microchip PIC to drive it with an Arduino, so will have something somewhat similar to your project on the bench here.
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #106 on: October 02, 2016, 08:02:06 am »
if what i saw when i googled that is right then i have some similar out of old microwaves
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #107 on: October 02, 2016, 11:53:25 am »
Current problem: Finding 16 small NPNs of the same type in my transistor 'odds&sods' bin with Hfe>100 and Vceo>45V for the hgh side VFD drivers. I've found a moderate stock of 2N929, but the Hfe's a bit low (40 - 120), and they're only good for Ic<30mA.

If you've still got any of the boards the small VFD came off, take a look at them and see if you are lucky enough to find a VFD driver chip0 you can use.   Its most often something fairly custom but occasionally you'll find a SPI one
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #108 on: October 02, 2016, 08:10:21 pm »
as i believe i have said i did not desolder these samsung 8 digit 14 segment ones but i have a couple microwave ones, 34s02 from nation semiconductors, mp7552 from TI,  D8049hc from NEC, hd61412op from hitachi and finally lm6059 (or lc6065 thats also there) from sanyo. im assuming their the vfd drivers given that their the biggest chip on the board, also i found nothing in my searches
« Last Edit: October 02, 2016, 10:17:28 pm by neo »
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #109 on: October 02, 2016, 08:39:20 pm »
D8049 is a fairly crappy MCU
HD61412 is an even crappier 4 bit MCU

You actually have to check which chip most of the VFD pis go to.  Its a long shot because if you are doing millions of units per annum, the cheapest option is to get a MCU with I/O pins that can go below ground. and run the filament at -30V or so relative to logic 0V, with the MCU pulling up to +5V and pulldown resisors on each pin to the -30V rail.  That's cheaper than open drain  HV outputs because it does't need external high side drivers.
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #110 on: October 02, 2016, 10:42:50 pm »
what about hitachi 7407 if it is what it claims on this datasheet then its a hex buffer/driver with open collect hv output
http://pdf1.alldatasheet.com/datasheet-pdf/view/122979/HITACHI/HD7407.html

also with the flip flops im going to assume CP= clock however when it comes to CD and SD im not sure what you mean though before we get too carried away with flip flops i have '595 chips meant to be here any day now
« Last Edit: October 02, 2016, 10:56:07 pm by neo »
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #111 on: October 03, 2016, 12:40:43 am »
Yes. Real Bipolar TTL 7407 or 74LS07 are hex non-inverting buffers that have have open collector outputs rated for up to 30V.  Their inverting equivalent is 7406 or 74LS06.   They wont directly drive a VFD because VFDs need a driver capable of sourcing current from the HV rail, but they make very good level shifters to drive either a PNP high side switch or a NPN emitter follower + diode pullup booster.
At 6 level shifters per chip, if you can find a couple of them  you could make a start with your VFD, but  you'd need 4 to do the whole job, + enough bits of shift register to drive them.   They are one of the few original TTL chips I bother saving when I find them.

N.B. as the HT for the VFD in the typical driver circuit 'stacks'' on top of the 5V logic supply to permit negative grid bias relative to the cathode to get good cutoff, using an '06 or '07 as the low side of your level shifter will effectively limit you to 25V Vak to avoid exceeding their 30V rating.

CAUTION: DO NOT USE any 74xx06 or 74xx07 with a 'C' anywhere in the 'xx' for level shifting as the CMOS equivalents have a parasitic diode from the output open drain to the Vdd rail.

The problem with 4000 series logic pin names (and to a lesser extent 74xx00 series), is that many of the manufacturers like to do their own thing.  The chips are generally fully compatible but they seem to want to call each pin something special of their own.
I was referring to the NXP (ex-Philips) datasheet: https://www.nxp.com/documents/data_sheet/HEF4013B.pdf and if you look at the pinout in that all would be clear. 

If you've got the time and inclination to hook up 4x 4013 in a chain as I described earlier with LEDs + resistors between their /Q outputs and +5V, before your '595 chips arrive, it will let you practice writing code to shift out data bytes.  However as you said they are short pinned pulls that you cant breadboard with, so that may be more trouble to you than its worth.   
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #112 on: October 03, 2016, 12:49:19 am »
i got 4 hd7407p and unlike the 4013 chips i have these are on a regular circuit board, with regular solder so i would be pretty confident at my abilty to get them off without over heating being a risk. The 4013 chips are part of old industrial circuitry.
« Last Edit: October 03, 2016, 01:02:47 am by neo »
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #113 on: October 03, 2016, 01:09:16 am »
Great.  Original 74xx series TTL is generally fairly tough so as long as you aren't pulling them by barbecuing the PCB, they should be fine.   Do they have long enough pins to be usable on breadboard or have they been cropped?  You can test them with a simple LED and 330R resistor between the outputs and +5v.  TTL inputs float high on their own, so all you have to do is ground each input pin and check the LED lights, without even the slightest glimmer when the input isn't grounded.

Do you also have EITHER 24x small signal PNP transistors with Vceo>-30V, 24x 33K or 47K resistors. 24x 10K resistors, and 24x 100K resistors OR 24 small signal NPN transistors with Vceo>30V, 24x small diodes and 24x 33K or 47K resistors?  If so you can build and test a practical parallel input driver stage for your VFD before any of the other parts arrive.  The PNP setup is simple but uses a lot of resistors.  The 33K to 47K resistors (any value in that range will do) go between the 7407 outputs and the transistor bases, the 10K resistors go base-emitter, all the emitters go to the HT rail and it also needs 100K from the collector to ground.  The PNP transistors invert, so logic '1' in will give 0V out and '0' in will give +HT out.

The NPN version uses the configuration I posted back in reply #29 (top 3 components only, driven by the '07 in place of Q2, with NO MORE THAN 30V for the HT rail.   At 30V the anode currents wont be so high, so Q1 needs less base drive, which is why I'm suggesting increasing R1 to the 33K to 47K range which also reduces the load on the +HT supply.  Depending on your VFD and the gain of your transistors you *may* be able to go up to as much as 100K, just check the voltage drop is acceptable when Q1 is ON and loaded by a working VFD anode.
« Last Edit: October 03, 2016, 01:14:01 am by Ian.M »
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #114 on: October 03, 2016, 01:14:50 am »
i have 80 or so mpsa42 npn transistors, as for the resistors id have to look around on old circuits to find enough, i dont have a great stockpile of loose parts but i have a gigantic stockpile of stuff on boards
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #115 on: October 03, 2016, 01:49:09 am »
MPSA42 is good, I must rummage through my shop clearance stock to see if I have any.  IIRC we had a little draw of them, but it may have gone to my ex-boss, as he cherry-picked the stockroom when we cleared it.

Its *NOT* worth salvaging ordinary 1/4W resistors.  The leads are almost always too short to do anything useful.   However I suppose you could scrounge enough parts to build one or two channels of the post#29 level shifter, extending the leads as required, just to gain experience with it.   

I've just finished sorting a couple of E12 resistor kits into a 12 compartment storage box, by first two digits, labelling each piece of bandoleer tape with the value for speed of access,  to have enough on hand for more complex projects.  Even at high-street prices it was under 2 cents a resistor, and I'll replenish any values that get used up individually, probably x50.  I also keep a good sized box of ex-breadboard resistors (with full length leads) that I tend to rummage through first when I just need a few of any value for anything non-critical so as not to chew through my sorted new stock. Once you've got your eye 'in', picking E12 three band resistors from a heap on a tray with a pair of tweezers is pretty quick - often quicker than getting a new part out.  I do however find 4 band codes a bit more of a PITA, expecially if there are E24 or higher series mixed in to confuse me. Some of the resistors in there have been my breadboarding companions for nearly 40 years - they get the  green pan-scourer treatment to clean the oxide off their leads before use.  I generally prefer to stick to the fresher ones, but I have more higher power ones from the old days.  I don't keep the few carbon composition stick 'body tip dot' resistors I inherited from my Grandpa in there, they aren't really suitable for breadboarding!
« Last Edit: October 03, 2016, 01:52:32 am by Ian.M »
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #116 on: October 03, 2016, 04:56:26 am »
i found 24 70k ohm resistors but their carbon (im guessing) if they wont do then i dont have any 40-70kohm resistors that will, or rather im sure i do but if it isnt on the surface then id have to go through three gigantic boxes looking for one value 24 times over which would take me days. Alternatively i could series a bunch of lower ohm ones
« Last Edit: October 03, 2016, 06:44:44 am by neo »
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #117 on: October 04, 2016, 07:46:45 am »
i could use a pin out for the HD7407P
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #118 on: October 04, 2016, 08:21:11 am »
Check the carbon resistors - they tend to go high with age.  If they are still in tolerance they are fine for breadboarding.   Just avoid using them for anything that is either important, or you plan to keep over a decade, or needs close tolerance parts.

Its 7400 series logic, second sourced by many manufacturers. Google is your friend, but just use the bare part number.  You should get several sources for the Texas Instruments or Fairchild version in the first page of results.  If you do a bit more digging and try hitachi 7407 datasheet you'll find the actual HD7407 datasheet.
« Last Edit: October 04, 2016, 08:27:23 am by Ian.M »
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #119 on: October 04, 2016, 07:48:16 pm »
The saga of my Arduino=>SAMSUNG SSED HNM-05SS62T VFD interface continues:
I didn't find any MPSA42 transistors, but I did find 450 of PIHER 2N4287, which are minature NPNs good for 45V Vceo, 50mA Ic, with HFE in the range 150-600 which should do nicely as the high side VFD drivers.   The anodes are getting 100K pullups, which should give me 1.5mA drive for 1V drop across the base pullup resistor, and when pulled low, pass 0.33mA to the ULN2803 collector.   The grids would probably work with the same, but I was short of 100K 1/8W resistors so decided to try a much lower value - 22K which should give 6.8mA drive for 1V base resistor drop.   The ULN2803 will be sinking 1.36mA to drive those.   All have small signal silicon diodes  base-emitter, k to b so the ULN2803 can pull the load down hard. 

The HT rail is from a AM1S-0524SZ 1W 5V:24V isolated DC-DC converter stacked on top of the 5V rail to give me 30V.  That should give me up to 42mA with 78% efficiency - a lot better than I could have cobbled together quickly and in a fraction of the breadboard area. The filament needs 60mA @ 1.5V, and to get started I'll be running it on DC  >:D so with a 60R series resistor as the 5V supply I am planning to use runs a little on the high side.  The resistor goes between one end of the filament and ground so the centre of the filament will be sitting up at approx 4.25V to give me some negative bias when a grid or anode is pulled low to get a proper cutoff.

Next job is to hook up all the VFD pins and the ULN2803 chips to the 12 high side drivers I've assembled and do a static test hard-wiring the ULN2803 inputs to light up various segment patterns, before I start hooking up the shift registers and Arduino.

I need to look at designing a 'Joule thief' style boost circuit for the HT which hopefully will be able to feed the filament from another winding - if I can get away with only three simple windings on a ferrite ring that will be great.  If it only produces just enough HT current for all segments lit, then I stabilise it with a 33V Zener, the filament drive should remain fairly constant.

Edit: The hardware is up and running - I tied the shift and store clocks together and clocked in random garbage by simply bringing my finger near the floating input wire (Joys of CMOS  :-DD )  Tying Din high blanked the display when I clocked it, tying it low lit everything and letting it float displayed random garbage.

The DC-DC converter was running a little warm, so I increased the digit grid base resistors to 150K - that's a little high so I need to find some more 100K sub-miniature resistors.  That part of the breadboard is a little crowded - I've got 12 transistors, 12 diodes and 12 resistors in 18 contact strips, it would be  4 less except that each driver needs two holes in the HT rail, so I really don't want to use normal 1/4W parts.

The Arduino in its little plastic protective frame is 'stapled' down with a heavy wire through each mounting hole and is hooked to the 74HC595 chain using its hardware SPI port. 

Now to write some software . . .
« Last Edit: October 05, 2016, 12:31:14 am by Ian.M »
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #120 on: October 05, 2016, 12:23:18 am »
when i say 70kOhm resistors i mean i went through and individually tester and found 24 resistors within a 10% tolerance, and when i actually build it ill either use modern ones or just make a note to replace them later
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Offline Buriedcode

  • Super Contributor
  • ***
  • Posts: 1610
  • Country: gb
Re: Vacuum fluorescent display to clock display
« Reply #121 on: October 05, 2016, 12:47:23 am »
I don't want to break the flow here, but Ian. M - you sir, deserve some form of medal for your patience, and careful explanations.  You have helped many of us out, but this is true dedication.

Neo:  I hope your project is going well. If you count the posts Ian has made, and the length of each one, just imagine how much time and effort has gone into this.  It is one thing to provide schematics, hints, and recommended part numbers, but Ian has had to change so many of his recommendations so far I'm amazed he has kept up.  I hope you're taking it all in!
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #122 on: October 05, 2016, 12:56:30 am »
I hope you don't mind me hijacking your topic to blog the build of my version.  At least it means I now have similar hardware to try stuff on if you get stuck writing the code.

Did you find the HD7407 pinout OK?
Don't worry about the carbon resistors, I'm using a mix of 100K and 150K with no problems so far so if they go high a bit it doesn't really matter. 

Ideally the resistors should be chosen to keep the load on the +HT supply constant.  When the open collector level shifter output is high, all the current goes through the segment, which takes I(seg) mA* by the nature of the VFD.  When the level shifter output goes low, the VFD segment doesn't get any current and the shifter has to sink whatever the resistor permits.  If you make the resistor V(+HT)/I(seg) (in K if you calculate with mA), the current will be the same as the segment would have took and the load on your +HT supply wont change.   In practice, I(seg) is not well controlled as it depends on filament temperature, +HT and aging, but for mains powered applications where efficiency isn't a big issue, you can certainly balance some or most of I(seg) and maybe get away with an unregulated or poorly regulated +HT supply.

* as specified in the VFD datasheet

What are you planning to use for your +HT supply?

@Buriedcode: No problem, its inspired me to get off my ass and build my own version, currently occupying most of a Boss Bimboard 3 next to my PC.  :-+
« Last Edit: October 05, 2016, 01:01:10 am by Ian.M »
 

Offline neoTopic starter

  • Super Contributor
  • ***
  • Posts: 1694
  • Country: us
  • The specialist.
Re: Vacuum fluorescent display to clock display
« Reply #123 on: October 05, 2016, 01:30:30 am »
Thank you ian, you are an excellent teacher and i am learning a lot despite my thick skull at some points, for the hv supply i was thinking of taking a 20 volt transformer i got from an oven if 20-30 (bridge rectifying amplification) isnt enough then i will probably use a cockcroft walton generator to step it up, alternatively i have a gigantic 30 v switching supply good for several amps (out of an old computer monitor) but im saving it i dont know what for but for something
Also yes i did find a datasheet though from TI rather that hitachi, and i dont mind at all that your "hijacking your topic to blog the build of my version."
« Last Edit: October 05, 2016, 02:42:24 am by neo »
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 12807
Re: Vacuum fluorescent display to clock display
« Reply #124 on: October 05, 2016, 03:09:00 am »
Cockcroft Watson doublers/triplers etc. need *VERY* large capacitors to work effectively at 50Hz or 60Hz, also for the few tens of mA you need, that's a horribly clumsy way of doing it unless the transformer is a micro-miniature 1 or 2 VA one.

My four digit VFD + driver is currently averaging 4mA from the +HT rail (I have a 100R resistor in series I simply measure the voltage drop across), so there is absolutely no way you need more than a few tens of mA for your 6 digit one.  To get started and find how much you actually need, either use a 30V bench supply with the current limit set at no more than 50mA, or if you don't have a 30V bench supply, use three PP3 9V batteries stacked in series.   They can be the absolute crappiest dollar store 'special' Zinc Carbon ones, though if you've got Alkalines on hand, you might as well use them.  If you split the battery clip so you have separate + and - clips, you can stack as many batteries in series by clipping them together as you need to get the +HT you want.  Connect battery - to Gnd or to +5V for more choice of voltages.   I'd start at 18V (2 batteries,  - to Gnd) then go up in steps till you are happy with the brightness.  You should see something at 12V Vak if the filament supply is correct, then up the voltage till you are happy.

Once you know what voltage your display likes, a small DC-DC converter is the best way of getting it.  Either order one or roll your own . . .

CAUTION: Don't exceed the voltage rating of your level shifters - 7407 is only good for 30V so don't go over 27V (three batteries, - grounded).
My ULN2803 chips are rated 50V and high side transistors 45V, so I can go up to 43V HT+ if I want to drive the VFD really hard.  However, I don't want to wear it out so I wont be doing that for more than a brief test.

I've currently got it counting in hex from 0000 to FFFF as I've hacked together a crude sketch to drive it.  I'll hold off posting code till I've fixed a few things - somehow I got the segment bits backwards so I've got seven VFD pins to rewire!  |O
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf