I'm going to make three clocks (Christmas presents for girlfriend, brother and sister), but I'll see if I can get samples approved with my university email. Thank you for your generous offer to send me some samples but I'll first try to get my own samples at a reasonable price.
Op dinsdag 19 november 2013 23:09:11 UTC+1 schreef Adam Jacobs: > > Hi Gideon, > How many of these clocks are you planning to build? If it is just a few, > then I wouldn't sweat the costs too much. Both of those companies (used to > be - I assume still) are very generous with samples. I agree that the > Supertex and Maxim parts can be difficult to obtain for a low price in > individual quantities from normal vendors. I've got a drawer full of > Supertex and Maxim samples, I'd be happy to mail you the parts. FYI, > requests for samples get a much more positive response if you use a company > or university email and describe a plausible project in the request. Any > time that I can't find some obscure part that is listed for a project, I > move to the obscure part manufacturer's website and request a sample. No > problem. > > Contact me off-list with your address & parts request and I'll see what I > can do. Of course, if you're designing a clock for mass production, then > all bets are off. :) > > -Adam > > On 11/19/2013 11:39 AM, Gideon Wackers wrote: > > I know the difference between a nixie and a VFD tube but I have to say > that your explanation is very nice to summarize all the loose bits of > information in my head. > > So If I have a 6 volt supply for my four filaments (in series) I would > not need a resistor. I think the 7806 won't get that warm with roughly > 400ma going through it but I can always take a simple switching psu for it > or attach it to my (metal) enclosure. I will simply use a DC filament > supply then to keep things simple (this project is going to be complicated > enough). > > My only remaining concern is the driving method, I would like to order > all my parts off ebay and/or tayda electronics. Places like mouser etc have > (in my opinion) ridiculous shipping rates so I would like to avoid them. > Another point is that the max6921 costs around 6-7 dollar a piece +1 euro > for a plcc socket, I am trying to keep the costs down a bit. So a method to > avoid using these drivers is preferred. > > HV5812: cheap but shipping costs are 40-50 dollar > MAX6921 expensive and/or high shipping costs > > > Op dinsdag 19 november 2013 20:06:50 UTC+1 schreef Adam Jacobs: >> >> Hi Gideon, >> >> I think that you have some confusion regarding how VFDs are driven. VFDs >> are not nixie tubes or anything even similar. Nixies are not vacuum tubes, >> they are cold-cathode (neon) tubes. With nixies, we place ~180vdc across >> the anode & cathode via a current-limiting resistor. The reason for >> current-limiting in a nixie is because as current increases, nixie >> impedance decreases, causing the neon tube to rapidly begin dissipating a >> catastrophic amount of heat. Nixies, being neons, regulate voltage to their >> maintenance voltage. Any reasonable voltage above the striking voltage will >> work fine. >> >> VFDs are triodes: Hot-cathode vacuum tubes. Ideally, the filament is >> driven with an AC supply of the designed voltage (via the two filament >> pins, usually a couple of volts) and the anode segments are driven with a >> voltage regulated DC supply at the designed voltage (usually 20-30v for >> direct and ~60v for multiplex). The grid is driven exactly the same as an >> anode segment and is used to turn the display 'on'. There are no >> current-limiting resistors used for driving the anode segments or the grid! >> >> In my VFD clocks, I used the trick (which I learned from here) of driving >> the filaments with DC. This works fine if you are using individual numeral >> VFD tubes, I wouldn't try it if you are using the big multi-numeral VFD >> display tubes. The (known) current draw of the filament is used for >> calculating a resistor-divider. One leg of the filament is tied to ground, >> the other leg to +5vdc via the resistor. If you go with this approach be >> sure to do your math on the front end. These filaments draw a lot of >> current, which means a lot of heat dissipation in the voltage-divider >> resistor. Driving this setup via a linear regulator supply would need a >> very large heat-sink. I would recommend using a switching supply like the >> LM2575. Obviously, if you have an AC supply that is the correct voltage for >> the filament then no resistor is needed. >> For a schematic: http://elbastl.sweb.cz/6-digit-VFD.zip >> >> I liked Maxim IC's 6921 driver IC. I know you specifically called it out >> as not an option, but it worked well for me. Specifically, I used the PLCC >> package because I work exclusively in protoboard and there are easy DIP >> PLCC sockets. There are numerous advantages in my opinion to the dedicated >> VFD driver chip. Instead of 8 dedicated GPIO pins (7-segments + grid), the >> 6921 uses a standard SPI interface. This would be even more advantageous on >> 16-segment VFDs. >> >> One thing you mentioned: Yes, 60v applied to the anodes will be VERY >> bright, even if multiplexed. I had to move my VFD clocks to bright places >> like my desk at work. a LOT brighter than equivalent nixie designs. I spent >> some time dialing back the supply voltages before finally giving up and >> accepting that VFDs are just designed to be bright. >> >> -Adam >> >> >> >> On 11/19/2013 5:09 AM, Gideon Wackers wrote: >> >> I want to build a four digit VFD clock (three of them actually) without >> using drivers like the max6921. I have two possibilities at this moment, >> one is this http://i.imgur.com/D4FGaV1.jpg and the other being this one >> http://i.imgur.com/5fMc7ty.png . Which would be best? >> >> Another question is the resistor that I will need: >> 0.0035/25*3 = 0.00042 >> 60/0.00042 = 140k = 130K or 150K ohm for R1 and 100k for R2 >> >> For the grids the same circuit applies but with a slightly different >> value for R1 due to the different current. >> But this implies that I use 60 volt. A few people said that the tubes are >> very bright at the recommended 50-70 volt for multiplexed tubes so if I >> lower the voltage to 40 volts I would suddenly need only 100K for R1. Will >> I bump into problems if I lower the voltage to lets say 40 volts but when >> my resistors are calculated for 60 volt? >> >> I want to make the filament supply with a 7806 and wires them in >> series, AC will be generated by four bs170 mosfets. Do I still need a >> filament resistor if I match my voltages this exact? >> >> Suggestions are welcome, my PCB can be roughly 9 by 5 cm so maybe there >> are other (cheap) alternatives to using resistors as drivers? I first got >> this idea because everything had to be stuffed onto a smaller pcb so maybe >> now that I have more space I can now use some IC's instead? >> -- >> You received this message because you are subscribed to the Google Groups >> "neonixie-l" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to neonixie-l+...@googlegroups.com. >> To post to this group, send an email to neoni...@googlegroups.com. >> To view this discussion on the web, visit >> https://groups.google.com/d/msgid/neonixie-l/62997dbb-f1ac-4b11-8e24-42f3eec74ad6%40googlegroups.com >> . >> For more options, visit https://groups.google.com/groups/opt_out. >> >> >> -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to neonixie-l+...@googlegroups.com <javascript:>. > To post to this group, send an email to neoni...@googlegroups.com<javascript:> > . > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/679846e1-8f29-4f22-b190-322f6477af14%40googlegroups.com > . > For more options, visit https://groups.google.com/groups/opt_out. > > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/5f92eacf-aa41-4fa6-9ae0-ea3156a195d5%40googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
