Hi, Thank you for your reply David. My reason for multiplexing was due to not having enough spare pins on the PIC, however having givin this considerable thought I have the IO pins that were being used to switch the MSD and LSD anode transistors and a third IO pin which was available to control the enable pin for the tayloredge SMPS, so by using these three pins allows me to to have 0 - 7 on the MSD which is great as I wanted 64 steps to indicate the volume control potentiometer position.
Sadly there is a but to this (is there not always) I need to be able to blank the digits which normally involves using all 4 bits of the 74141. Now as I do not need 7 - 9 I was thinking I could shift all the digits along one position, so 0 in the nixie is connected to 1 on the 74141 1 to 2 and so on. This results in being able to blank the nixie by sending 000 to ABC and having D permanently tied to ground. This digit shift being easy to work around in the firmware. I can position the SMPS in such a way that it will not interfere with the audio signal path so I would like to try and stick with it for the nixie HT supply as the valve HT supply has a delayed start to give chance for the soft started heaters to warm up. I want the volume indication to come on at power up with a possible count down on it to show the remaining warm up time. Additionally to this I am trying to keep the analogue and digital power rails separate from one another. This is where my questions begin: Can I leave the cathodes 7 - 9 floating or do they need to be tied to something? Will floating digits ghost? I would also like to keep my enable signal to disable the SMPS when the amplifier is in standby so can I use the now unused 0 output on the 74141 as a logic signal to drive the enable pin on the SMPS? The only trouble with this is when blanking the nixie the SMPS will be disabled unless I use extra logic to look at the LSD bits? (I guess it is quite environmentally friendly to turn the SMPS off when the digits are blank but if I was worried about this then I guess I would not be building a power hungry inefficient valve amplifier!) Regards, Tim On Wednesday, 2 January 2013 22:25:13 UTC, nixiebunny wrote: > > On 1/2/13 3:01 PM, Tim wrote: > > I am in the process of building an audio preamp using valves and I am > > using nixie tubes to indicate the volume control position. I am using > > two nixie tubes to indicate the volume and they are being multiplexed > > via a PIC and 74141. > > > > My question to you fine folk is how should I provide power to the nixie > > tubes. I have two options available to me: > > > > > > Regards, > > Tim > > Tim, > > If you can afford the extra four pins on the PIC and another 74141, then > you can run the tubes direct (non-multiplexed) and not worry about it. > > If you will be multiplexing them, then the power supply will not conduct > the noise to any noticeable extent. You will need a high anode resistor > value, so you can insert a simple two-stage RC low-pass filter (10K > series, 0.1uf polyester shunt) between the power supply and the anode > resistors to eliminate noise from the anode power. > > You will want to be careful about mounting the display unit away from > the input stage of the amplifier, to prevent radiated noise from getting > into the input stage where it will be amplified. > > -- > David Forbes, Tucson AZ > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msg/neonixie-l/-/wzW1euMoJw0J. For more options, visit https://groups.google.com/groups/opt_out.
