Welcome to an addictive hobby! The anode-driver will need some rework because the NPNs (T1 thru T6) will only drive-out 4.3V (5v I/O from the ATMega, minus 0.7Vbe = 4.3V) as the circuit is shown. With multiplexing, you will need what's known as a 'high-side driver', and often that is done with PNP or PMOS devices.
On the schematic, you would swap collector & emitter pins and change the NPN to a PNP. Next, you would need to add a base-resistor between the digital logic, and the base. This is to limit the base-current to a proper value. For a 170V supply, a maximum of 4mA per tube, and a rough-guess of transistor beta of 50, you would need 80uA of base current. That would be about 2Meg ohms for the base resistor. The exact value isn't critical. Lastly, you will need a high-voltage logic driver to control the PNP transistors. When the PNP is off, the voltage seen by the logic-driver will 'see' about 170V, which means regular logic gates *might* get damaged. In reality, the ESD protection of the 74HC238 would sink the 80uA into the 5V supply and turn all anodes on. You could use an HV5530 to drive the PNP transistors, as well as the tube cathodes. Which means you can get rid of T8 thru T17. A single HV5530 has 32 outputs. Now, you dont need to display 0000 thru 9999 for a clock, so some cathodes can be left undriven. For example, on a clock only digits 1 & 3 need to display all 10 numerals. Digit 2 displays 0 thru 5, and digit 4 displays 0-2. So you could drive all required cathodes for a clock with only 29 pins on the HV5530, in other words, direct-drive. So you can get rid of the PNP devices as well and make the design much simpler. -- 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/c526ca02-0d87-48cb-b587-1e2391ababa6%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
