Those values were left over from the 5v circuit. I was more concerned with the level shifting from the PIC at 0 to +5v. Peter
On Mon, Feb 15, 2021 at 6:48 PM Jon <dekat...@nomotron.com> wrote: > I'd had a similar thought about increasing the bias resistors - it's not > necessary to run so much current (5mA) through that part of the circuit. > > OK, so your proposed conditions are that the dekatron will see are 400V > anode to main cathodes; guides swinging from +25V to -25V with respect to > main cathodes. Tube current will be about 345uA. > I've replicated these on my dekatron tester using a nice NIB GS10C/S as > the test subject and can confirm that they do work - the tube stepped fine > up at speeds up to over 4kpps once I'd woken it up a bit. > > Caveats: > 1) I only tried one tube. > 2) My circuit is rather different to yours so although the static voltages > are the same, the pulse shapes are almost certainly different. And we > didn't even talk yet about pulse durations, so I've no idea what your PIC > is spitting out. But as long as you're not trying to cut things too fine, > there's lots of latitude to find patterns that work. Keep things north of > 100us per phase and you'll be fine unless you've got a really reluctant > tube. > 3) I was running at slightly lower current (300uA) so you've probably got > a bit more margin for speed than I had. Recommended operating conditions > are 325uA +/- 20%, so we're both inside that range. But a little more > rather than less current is useful when pushing higher speeds. I'm guessing > though that you're looking for a much slower stepping speed for this > application though. > > If you've not already done so, I'd definitely second Martin's > recommendation to take a look at Michael Moorrees' dekatron work (he looks > in here from time to time too). He used a couple of elegant design tricks > which simplify the interfacing of dekatrons to modern electronics / > microcontrollers - I've followed his approach in pretty much all the stuff > I've built and it works a treat. Not to say that other approaches aren't > equally useful too of course. > > Jon. > > On Monday, February 15, 2021 at 9:39:13 AM UTC Dekatron42 wrote: > >> I'd raise the resistance to at least some 100k for the two bias resistors >> R5 & R6 in your diagram above. >> >> I'd also use the correct bias voltage and just use an MPSA42 with its >> emitter to common ground for the driver to simplify the circuit as Ronald >> Dekker and Michael Moorrees with their dekatron circuits. >> >> Different dekatrons need different bias and pulse voltages on the guide >> electrodes to count properly so accomodating for those requiremenst will >> remove a lot of problems and keep down the fault finding time. >> >> /Martin >> On Monday, 15 February 2021 at 03:05:12 UTC+1 bung...@gmail.com wrote: >> >>> You are absolutely right. 5v was not high enough despite Ronald's and my >>> confirmation that it would work. >>> I am changing to +25v and -25v and will have an optocoupler with the >>> diode driven from the 5v PIC and the transistor at the bottom of the >>> resistor between the two power supplies. It keeps it simple. I have to >>> order the optocoupler because none of my old ones have higher than 30 v >>> rating. >>> I will have to think about the extra two power supplies. Maybe I can't >>> avoid them. It will be a few days until I get the parts. >>> Peter >>> [image: Dekatron Circuit.jpg] >>> >>> On Sun, Feb 14, 2021 at 3:18 PM Jon <deka...@nomotron.com> wrote: >>> >>>> Interesting approach - not seen it rigged up quite like that. Let us >>>> know how it goes! >>>> >>>> My immediate question is whether there's a big enough potential >>>> difference between an inactive guide and a main cathode to get a reliable >>>> transfer forward from a deactivating G2 to the 'next' main cathode rather >>>> than back to the adjacent recently used G1 - 5V is much lower than the >>>> datasheet guide bias. Might be OK at slow stepping speeds with long guide >>>> pulses. Also the leading edge of your guide pulses is going to be fairly >>>> slow as Q1/2 come out of saturation and the guides are passively pulled >>>> down to the 'active' voltage. Most guide drive circuits use a NPN pull-down >>>> to the active state which creates a sharp leading edge and then a slower >>>> return to the inactive state. >>>> >>>> Jon. >>>> >>>> On Sunday, February 14, 2021 at 7:06:28 PM UTC bung...@gmail.com wrote: >>>> >>>>> Having finished the Amperex 8453 display I started on my Dekatron. >>>>> Thanks to all for the suggestions. >>>>> I read up on Ronald Dekker's clock project >>>>> https://www.dos4ever.com/decatron/decatronweb.html >>>>> and decided against a direct drive from a 74141 because, even if it >>>>> was practical, it would not look as good as using all the pins. It would >>>>> look like the 8453 I just finished except without the number mask. >>>>> A few quick experiments showed that a -24v power supply was needed for >>>>> the easiest implementation.. This is my design. I will let you know if it >>>>> works. >>>>> >>>>> A PIC drives the circuit: it starts with Q3 off to force a start at 1. >>>>> A high on R3 or R4 is the same as the switches in Ron's test circuit >>>>> placing -24v on the guides. As my PIC sends the BCD for the other displays >>>>> and clocks the E1T it will generate the sequence to advance or retard this >>>>> Dekatron.. >>>>> [image: Dekatron Circuit.jpg] >>>>> >>>> -- >>>> 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 view this discussion on the web, visit >>>> https://groups.google.com/d/msgid/neonixie-l/62979e37-ef21-46e1-9b7c-45a4c4080238n%40googlegroups.com >>>> <https://groups.google.com/d/msgid/neonixie-l/62979e37-ef21-46e1-9b7c-45a4c4080238n%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> -- > You received this message because you are subscribed to a topic in the > Google Groups "neonixie-l" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/neonixie-l/dQn3tFBYfoc/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > neonixie-l+unsubscr...@googlegroups.com. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/75f258db-83ea-4df3-9d50-52dcaed1461en%40googlegroups.com > <https://groups.google.com/d/msgid/neonixie-l/75f258db-83ea-4df3-9d50-52dcaed1461en%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. 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