#avr Logs

May 24 2019

12:48 AM rue_shop1: polprog, I have a circuit I'm gonna show ya
12:53 AM rue_shop1: polprog, remember that the CENTRE voltage of the filaments ac supply should be at 5V
12:53 AM rue_shop1: you can capacitor isolate it
12:53 AM rue_shop1: the lm393 make good oscillators, up to 2.5Mhz
01:11 AM rue_mohr: arg, I forgot to grab that schematic
03:13 AM eichiro_ is now known as eichiro
03:34 AM polprog: 07:42 < rue_shop1> polprog, remember that the CENTRE voltage of the filaments ac supply should be at 5V
03:34 AM polprog: what do you mean?
03:35 AM polprog: ah i think i know
03:35 AM polprog: yeah in this design even if the osc failed, tit would just get to 2.5V DC which is good
03:35 AM polprog: it would*
03:35 AM polprog: no tits here
06:19 AM day: polprog: wouldnt a center voltage of 5V mean (5V +- 2.5V)?
06:20 AM day: so incase of 0 VAC you end up with 5V DC and not 2.5V DC
06:39 AM polprog: yeah
06:39 AM polprog: but why have 5V dc bias on the filament
06:40 AM polprog: it will just make the voltage between grid and filament 5V lower
06:41 AM polprog: right now the filament is driven by an h bridge that puts 2.5V on its sides with alternating polarity
06:41 AM polprog: i dont know why would the centre voltage need to be at 5V
06:54 AM day: is AC even a requirement?
06:56 AM polprog: not really, it works wth DC but larger segments light up uneven
06:56 AM polprog: and its a sort of elegant solution
06:56 AM day: right, i think ive read something about thta
06:57 AM day: but i think the center voltage should be 0V :/
06:57 AM polprog: why
06:57 AM polprog: or rather, 0V in reference to what :D
06:57 AM day: why would you need a DC voltage on the filament?
06:58 AM polprog: there needs to be a DC difference between the filament and grids/segs
06:58 AM polprog: the filament is a cathode as well
06:58 AM polprog: not a spearete heater like many valves have
06:58 AM day: its the electron emitter iirc
06:58 AM polprog: yeah
06:59 AM day: but as long as it is powered it will emit
07:00 AM polprog: yes, but there needs to be a voltage difference between the grids and the filament so that the electrons can be attracted to grids
07:06 AM day: but doesnt the more even illumination is a result of having the electron flow switching directions in the filament?
07:07 AM day: but isnt*
07:07 AM polprog: yes, thats what the h-bridge is doing
07:08 AM day: and with a center voltage of 5V +-2.5V you would only end up with a "pulsing"
07:09 AM day: maybe my electronic understanding has some fundamental flaws though :p
07:09 AM polprog: im not sure what is the centre voltage now
07:09 AM polprog: i reckon 2.5V *0.5
07:09 AM polprog: cause the filament ends are once at 2.5 and once at 0V
07:09 AM polprog: alternating
07:11 AM day: i would interprete that as a center voltage of 0V because it should be equivalent to -2.5V/+2.5V against GND
07:12 AM day: or 0V/5V against 2.5V
07:14 AM polprog: hmm
07:39 AM day: in a sense this would also be identical to putting DC on the filament and physically rotating it ^.^
08:05 AM polprog: day: yeah thats what i figured out as well :D
08:50 AM rue_mohr: polprog, its AC
08:50 AM rue_mohr: polprog, it goes up and down by, lets say 2V
08:50 AM rue_mohr: so when that is centered at 5V
08:50 AM rue_mohr: it means it goes from 6V to 4V
08:51 AM rue_mohr: not 0V to 2V
08:51 AM polprog: why not
08:51 AM polprog: anyway, thats a case ow changing gnd on the bridge to vfil and putting 5v on top
08:51 AM polprog: of*
08:51 AM rue_mohr: the 5V bias to because your supposed to have the segments negitivly biased when their off
08:51 AM rue_mohr: the bias is fromt he filament
08:52 AM rue_mohr: this sounds like a good thing to cover in my document
08:53 AM rue_mohr: polprog,
08:53 AM rue_mohr: did you see this...
08:54 AM rue_mohr: http://ruemohr.org/~ircjunk/oldsite/vfd.htm
08:55 AM rue_mohr: funny enough, the filament AC does not need to be sine wave, it can be out-of-sync square wave
09:30 AM polprog: rue_mohr: have you seen my schem?
09:46 AM Sam47 is now known as sam_vagabond
09:46 AM sam_vagabond is now known as Samed
09:46 AM Samed is now known as Sam47
09:46 AM Sam47 is now known as sam_vagabond
02:37 PM day: polprog: https://www.noritake-elec.com/wp/wp-content/themes/noritakeelec/inc/part/operation/img/fig38.gif
02:37 PM day: i dont believe the DC filament offset thing
02:37 PM day: source: https://www.noritake-elec.com/technology/general-technical-information/vfd-operation
02:40 PM day: obv. the waveform does not matter at all
02:41 PM polprog: yes
02:41 PM polprog: me neither. The bias would lower the voltage between thr filament and grid
02:42 PM day: well i just stumbled over 5.3 on the noritake page
02:42 PM polprog: but it can allow more power thru the filament, so both approachea are fine
02:42 PM day: that seems to show some offset, but i havent quite gotten why
02:43 PM cehteh: mhm
02:56 PM polprog: no, its a centre tapped trafo, theres no offset
02:57 PM day: polprog: i mean the little graph, the V1 looks larger than V2
02:58 PM polprog: the second graph
02:58 PM polprog: fig 13?
02:58 PM day: yes
02:59 PM polprog: the areas are the same, V2 is lower so its longer, V1 is higher so its shorter
02:59 PM day: true. but why is it lower in the first place?
02:59 PM polprog: hmm, no idea
05:05 PM polprog: i wonder if i put diodes on both sides of the inductor could i get performance
05:05 PM polprog: probably not
05:25 PM cehteh: you mean drop performance? :)
05:26 PM polprog: why drop :p
05:26 PM cehteh: 2x diode drop
05:27 PM polprog: not like that
05:28 PM polprog: forget it, it was nonsense
05:28 PM cehteh: is the filament heated or cold?
05:34 PM polprog: heated
09:38 PM day__ is now known as day
11:26 PM day__ is now known as day
11:40 PM rue_mohr: polprog, your schematic assumes standing wave tho :)
11:44 PM rue_mohr: Everyone seems to be interested in ignoring my advice....
11:46 PM rue_mohr: er, heh, woke up, yea, Its not standing wave its votlage divider heh
11:54 PM rue_mohr: I dont think its worth posting how to create a transformer that would do filament drive and voltage boost at the same time
11:59 PM rue_mohr: I wonder why the pushpull driver didn't work for you
11:59 PM rue_mohr: second pass we had the coil polarities right