IceTube Clocks

Revisiting IceTube clock designs and con­struc­tion, after per­form­ing some small repairs on an IceTube clock I built back in 2010.

IceTube clock built in 2010
IceTube clock built back in 2010, with 3D pow­der print­ed clock enclo­sure in background

After replac­ing a pow­er sup­ply fil­ter capac­i­tor and improv­ing the heatsink on the TO-220 5 volt reg­u­la­tor, on a clock I built in 2010. I decid­ed to revis­it the design to see what improve­ments I could make after 10 years.
The orig­i­nal IceTube clock was designed by Limor “Ladyada” Fried of Adafruit. There are sev­er­al oth­er sim­i­lar designs with dif­fer­ent enclo­sures, but this one was the most pop­u­lar, as it was devel­oped as a kit by Adafruit. Over the first few years there were many firmware and hard­ware updates of the orig­i­nal design, such as GPS syn­chro­niza­tion, auto dim­ming, and improved firmware.
My orig­i­nal clock with auto dim­ming was a ver­sion 1.1 and I end­ed up build­ing 12 of them for Christmas presents that year.

Version 1.31 IceTube clock with DS32kHz TCXO mod­ule attached

I had held on to a sec­ond 3D print­ed enclo­sure that I had print­ed 9 years ago, that was designed by Nathan Matsuda (NMATSUDA) and shared on Thingiverse. It was designed for the orig­i­nal ver­sion 1.0 board, but had some very restric­tive height issues. The enclo­sure was print­ed on a Z Corp. Spectrum Z‑510 pow­der 3D print­er, and then impreg­nat­ed with an epoxy resin to improve it’s strength.
While the main and side cir­cuit boards were func­tion­al as orig­i­nal­ly designed, I thought that there were sev­er­al areas that could use some improve­ment. Most of the orig­i­nal pow­er traces were between 16 and 10 mil width, and the 5 volt TO-220 reg­u­la­tor was dis­si­pat­ing quite a bit of heat.
I great­ly improved the ground plane and increased the size on all of the pow­er traces, and most of the oth­er cir­cuit traces on the board. I also mod­i­fied the board to use a switch­ing volt­age reg­u­la­tor for the 9 volt to 5 volt sup­ply along with improved input and out­put fil­ter­ing to reduce rip­ple voltage.

close up of DS32kHz mod­ule attached with shield­ed twinax cable, and sep­a­rate 5 volt wire
DS32kHz mod­ule top view
DS32kHz mod­ule bot­tom view with 1220 coin cell bat­tery back­up bat­tery holder

I had sev­er­al of the Maxim Integrated DS32kHz dip ver­sions of their tem­per­a­ture-com­pen­sat­ed crys­tal oscil­la­tor (TCXO) mod­ule with an out­put fre­quen­cy of 32.768kHz. So I decid­ed to put togeth­er a small cir­cuit board that would fit into the unused enclo­sure end near the 9V pow­er jack. The board breaks out the 5V, ground, 32 kHz sig­nal pins, pro­vides a 1220 bat­tery hold­er, and ties all the unused pins to ground as required in the datasheet.
This board replaces the 32.768 kHz crys­tal, and two load capac­i­tors on the main board and pro­vides an accu­ra­cy of ±1 Minute/Year from 0°C to +40°C.
The 32kHz out­put pin of the board is con­nect­ed with a shield­ed twinax cable con­duc­tor to pin 9 (PB6 / XTAL1) of the ATmega328P micro­con­troller using the exist­ing emp­ty crys­tal con­nec­tion. The ground pin on the DS32kHz board is con­nect­ed to the main board using the sec­ond twinax con­duc­tor to one of the emp­ty load capac­i­tor ground con­nec­tions, and the twinax shield is con­nect­ed only to the sec­ond load capac­i­tor ground con­nec­tion. There is no con­nec­tion of the twinax shield to the DS32kHz board. The 5 volt input on the DS32kHz board is con­nect­ed to the 5 volt reg­u­lat­ed out­put of IC3.

IceTube clock Version 1.31 main board lay­out top
IceTube clock Version 1.31 main board lay­out bot­tom

I also removed the ISP con­nec­tor on the main board to make room for the addi­tion­al pow­er sup­ply fil­ter­ing. My ATMEGA328P is sock­et­ed and fair­ly easy to remove for repro­gram­ming so I decid­ed it was a good trade-off.
My orig­i­nal firmware was assem­bled by DigiSage on the Adafruit forums and includ­ed sev­er­al fix­es and mods by him­self and oth­ers such as a sec­onds dis­play mod, reset issue fix, clock cal­i­bra­tion menu, and pho­tore­sis­tor auto-dim.
For the ver­sion 1.31 clock I used a new­er ver­sion of firmware by jarchie also from the Adafruit forums. The XMAS-Icetube firmware can be com­piled for use on the orig­i­nal ver­sion 1.1 boards, or jarchie’s updat­ed Rev. D hard­ware boards. (Next Project)
I was able to find some low pro­file capac­i­tors by Nichicon that would fit the lim­it­ed height of the enclo­sure and fin­ished assem­bling the main board.
The IV-18 VFD tubes were pur­chased on Ebay from a sell­er in Russia with a three week ship­ping time, but arrived in excel­lent condition.

Painted enclo­sure for IceTube clock com­plet­ed with DS32kHz mod­ule installed
IceTube clock IV-18 tube con­nec­tor end stuffed full of rib­bon cable
IceTube clock pow­er sup­ply end with DS32kHz TCXO board mount­ed with 3M VHB tape on the flat below the tube

I paint­ed the enclo­sure with “Krylon” Metalic Oil Rubbed Bronze paint, and attached the end­caps with Black-oxide M4 * 0.7mm * 25mm sock­et head screws.
Since this was a spe­cial­ized one-of-a-kind build, I will not be pro­vid­ing a BOM, but all updat­ed com­po­nents are list­ed in the EagleCAD schematics.

After fin­ish­ing this build I decid­ed to build some more IceTube clocks as gifts using jarchie’s updat­ed Rev D hard­ware as a start­ing point for the new design. (Coming soon…)

Icetube Clock Enclosure by nmat­su­da on Thingiverse
Icetube Clock Enclosure by nmat­su­da on Shapeways
EagleCAD schemat­ic and board IceTube clock files for Version 1.31
EagleCAD schemat­ic and board DS32kHz files Version 1.0
jarchie Xmas-IceTube-firmware source files
Adafruit build tuto­r­i­al for Ice Tube Clock V1.1

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