construction manual since it contains many tips and
examples that may be of use to you in this or other
projects. None of the SMDs used here are ridiculously
difficult to solder by hand, but it does require a steady
hand, good light, a magnifying glass, and a good soldering
My Weller soldering station has replaceable tips, and
the tip I use for the SMD parts is almost needle sharp.
Combined with very thin solder (0.020”), it is really not
too hard to do (Figure 15). I have included additional tips
in the construction manual at the article link. When
ordering the SMD capacitors, order a few spares. If you
lose an SMD capacitor during construction, look at the
end of your soldering iron first. If it’s not there, best go get
I usually buy things like the small SMD parts in kits
from online providers; it provides lots of spares that way.
Speaking of online providers, eBay is a good source for
inexpensive parts if you are not in a rush. Since you will
probably get your Numitrons there (Figure 16), other parts
can be ordered at the same time. LEDs can be found on
eBay for very cheap, but it’s definitely “buyer beware” in
my experience; many are junk.
Don’t buy the “1,000 for a dollar” deal because you
will be disappointed. I have included Mouser part
numbers for many of the components if you prefer not to
take chances. Of course, there are many other excellent
vendors to choose from as well (check the advertisers in
Another important thing to keep in mind is static
protection — especially in the winter when houses
become dry, and static discharges (even so small that you
can’t feel them) are guaranteed to destroy or damage
many of the parts in this project.
Numitron vs. Nixie?
So, now that you’ve had a chance to look over this
clock, you might be considering building one ... but
maybe you had your heart set on a Nixie tube clock.
Though Nixies are very cool and retro in their own right,
the Numitron tube clock has the same feel while offering
• They are low voltage devices, so — unlike Nixie
tubes — you do not need to insure carefully insulated
enclosures to keep users from getting a nasty high voltage
• They do not suffer from failure states such as
“sputtering” where electrode metal collects on the inside
of the glass tube dimming or obscuring the display.
• They don’t encounter cathode poisoning that
requires a potentially distracting anti-cathode poisoning
• In many cases, Numitrons will outlast Nixie tubes as
they are typically rated for over 100,000 hours (~ 11. 5
years) of operation compared to some Nixies that are
rated for only 5,000 hours (~200 days!).
All in all, Numitrons are a fun and interesting item,
and having them used in a clock while surrounded by high
tech LEDs makes for a great conversation piece! I highly
recommend Numitrons even if you already have a nifty
If you do end up building a Numitron clock of your
own, please let us know! NV
■ FIGURE 15. The tools I use for surface-mount components
I am considering helping out those who need assistance
with this project. This could be with programmed PICs, or
perhaps boards that are partially assembled (SMD parts)
on an individual “first come, last served” basis. (All I can
promise for sure is that although I'm not very good, I am
definitely slow!) You can contact me at TheOldPhart2@
gmail.com if you have any questions or suggestions.
34 September 2016
■ FIGURE 16. Typical set of Numitron tubes
available on eBay.