74 series logic is standard TTL, so 0 to 0.6 volts is a good
logic zero, and anything above 2.4 volts (preferably 3.2 to back
bias an internal diode) is a logic one.? IIRC, 7447 outputs are
simply saturating transistors to ground, with the anode of the
display switched on or off to enable the digit if scanning.
Harvey
On 3/16/2023 5:27 PM, Michael A.
Terrell wrote:
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What about the 7441/74LS41 BCD to decimal decoder designed
to drive Nixies?
I have a 312B, which uses LED displays, with a much simpler
counter design.which uses the 74LS75 Latch and the 74L47 BCD
to seven segment decoders. The 312A manual that I have is so
speckled tht I can't read it to determine the logic levels.
On Thu, Mar 16, 2023 at
12:57?PM Greg Muir via <big_sky_explorer=
[email protected]>
wrote:
Brad,
?
If
I can recall the neon-photocell approach was very
similar to that used in the HP 5245L counter series
display boards.? If you can find an old
board (base P/N 05212-6016) you might have some luck in
finding similar photocell devices.? The
suffix to the part number (¡°Series 6xx¡±) changed
reflecting the board functionality.? There
was also changes in the design of these boards where
they either contained an enclosed module termed
¡°Decoder¡± (One HP part number is 1820-1683¡±)? or
a ¡°Photoconductor Plate¡± where the photocells directly
drive the Nixie tubes.
?
It
appears that HP changed to the ¡°Decoder¡± module in later
model counters.? It is a black plastic
enclosure on the board with a removable cover but I have
never opened one up to see what is inside.? Given
its construction I am assuming that it, too contains
photocells.
?
Greg
