Yeah Chuck.. but the interesting thing is that it is supposedly very closely
based on a TI ap note or some such.
I was looking forward to some input from the seller. But maybe this is
public and wasn't "addressed" to him.
Still think it is/was in his interest to comment though.
John K
----- Original Message -----
From: "chuck richards" <chuc...@all2easy.net>
To: <neonixie-l@googlegroups.com>
Sent: Friday, March 31, 2017 10:12 PM
Subject: [neonixie-l] Re: Taylor Edge Nixie Clock Kit
360 ohms is way too little resistance for *any* sort of
TTL pullup resistor! That apparently got confused with
the standard *pull down* resistor used to keep an unattended
TTL input *low*. 360 ohms for a TTL pulldown is just right.
2.2k ohms is the standard value to use as a TTL pullup.
That goes for regular old 7400 series TTL, as well as 74LS
series.
The old military practice was to always use 1k ohm as the
standard TTL pullup resistor value. Note that even when using
that 1k pullup resistance, that all we are asking of any TTL
gate which is pulled up by this, is to be able to provide 5
milliamperes
in order for for the output to go low.
Even that value of 1k ohm would work ok with either plain 7400 or
74LS.
2.2k is much more like it, however.
At that value, all we are asking is 2.3 mA, and that works fine.
360 ohms is just simply too close to being a piece of wire!!
(This is all explained in great detail on page 12 of Don Lancaster's
famous TTL Cookbook)
---- Original Message ----
From: neonixie-l@googlegroups.com
To: neonixie-l@googlegroups.com
Subject: [neonixie-l] Re: Taylor Edge Nixie Clock Kit
Date: Thu, 30 Mar 2017 19:38:26 -0700 (PDT)
I'm a little late to the party, and the discussion between old 74xx
versus
74LSxx caught my attention. In most cases, I'd favor the newer 74LS
over
the original 74xx. But the resistor values (360 ohm) paint you into
using
the older series, because 5V / 360ohms gives you 13.9mA. The value
seems to
have been chosen because of the set switch resistor values.Of course
as the
OP mentioned, removing all the 360 ohm resistors lets the unit
operate
properly. The set switches may work adequately, too.
<https://lh3.googleusercontent.com/-k_4j6X4xaEs/WN3AZVxQbgI/AAAAAAAAY
lU/Wcu3xmkZidsfPKYgHCTU5VlWEi_nSXiWACLcB/s1600/Taylor_Clock.jpg>
Personally, I prefer 4000 series CMOS, for this kind of thing.
Good to see that the OP, and his buddy, figured it out.
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