Hello and thank you for your pointers - right now, the display seems to be running evenly and looks good - no significant heat is being generated in the electronics though presence of a bunch of 5W resistors seems somehow out of place when the display should only be using mA ! - Richard
On Friday, 31 October 2025 at 23:27:28 UTC Dekatron42 wrote: > I've dug through my documents and I've been thinking about that 1M > resistor in the cathode keep alive electrode and its effect on the driving > of these tubes and I think it is an error to have it there as, even though > it will only flow a very low current through it, it will affect the common > ground point for all of the driving circuits and that will affect the level > depending on how many bars that are lit up. I've never seen a circuit that > incorporates that 1M resistor in the keep alive electrode for the cathode > and thinking about it it looks incorrect. > > Please correct me if I am wrong but that is my opinion on how these tubes > should be driven. > > /Martin > > On Friday, 31 October 2025 at 13:26:11 UTC+1 leo oel wrote: > >> IGT1-203 Self Scan bar graph display >> >> https://dotdisplay.blogspot.com/2017/08/igt1-203-self-scan-bar-graph-display.html >> >> пятница, 31 октября 2025 г. в 12:27:23 UTC+2, Dekatron42: >> >>> There are few professional designs in the audio business and in the >>> ventilation flow control business who completely skip that extra 68V supply >>> - I haven't checked the data-sheet what it says but they don't bother with >>> that extra voltage. Some designs use a SN75468/9 IC (75469 in case of CMOS >>> and 75468 if TTL is used) instead of transistors and no pull-up resistors, >>> just hook the 68V signal to the common pin on the SN75468/9. >>> >>> For all of the designs I've seen there is not one that uses a 1M >>> resistor on the keep alive cathode, only on the anode, they all just ground >>> the keep alive cathode pin directly. >>> >>> Some designs uses a voltage between 50-80V for the 68V voltage. Some >>> designs uses a voltage doubler/tripler to supply all voltages from a low >>> voltage AC transformer, so maybe use a switcher with say 62.5V DC output >>> and the quadruple that to 250V DC if there is the possibility of hooking >>> into the circuit before rectification/smoothing? >>> >>> /Martin >>> On Friday, 31 October 2025 at 06:57:04 UTC+1 Richard Scales wrote: >>> >>>> Does anyone have any experience in driving these panaplex-like bargraph >>>> displays? >>>> >>>> I have some IGT2-203R and am using a well publicised circuit from here: >>>> https://stromrichter-org.translate.goog/attachment.php?aid=4116&_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=wapp >>>> >>>> [image: Pic1.jpg] >>>> >>>> I have made various changes, I'm using an Arduino Nano for the >>>> controller, an HV module for the 245V and I changed out the R2/D2 >>>> combination for an LR8 HV regulator as I found that R2 was getting a lot >>>> warmer that I would like. >>>> >>>> Now I am looking at the anode supply which is controlled by R8+R18 (I >>>> am only using one channel so don't have R7/R17. >>>> >>>> It seems that when Q8 is off, the Anode is connected to the 245 supply >>>> via 36K for current limiting purposes - that's all good. When Q8 is on, >>>> then the anode is fed from what is now the voltage divider combination of >>>> R8+R18 (98V) - also good. >>>> >>>> However, that combination of 24K+36k is drawing about (245/60)mA - 4mA >>>> - the power being almost 1W - so they get a little warm. I have over >>>> specified and used 5W parts. >>>> >>>> What I have works just fine, and, in fact I even doubled up on the >>>> resistors to share the load even further but I wonder if there is perhaps >>>> a better way which might not generate quite so much heat? >>>> >>>> It might seem overkill but I could make 98V using another LR8 and then >>>> use high side drivers to 'switch' between the two (like a couple of Opto >>>> Couplers or a bunch of 42/92 transistors). >>>> >>>> ... or am I being over cautious? >>>> >>>> - Richard >>>> >>>> -- 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 [email protected]. To view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/8c548e61-3ebe-4b0b-966d-a7cedd70c925n%40googlegroups.com.
