ICE Tube Clock Oscillator Modification

[bikegeek]

I made my second mod to my ICE Tube clock last week (first was the dimmer mod with digisage firmware as you may notice in my pic.)

I replaced crystal Q1 with a Maxim DS32kHz Temperature compensated crystal oscillator (see: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2940). Although it's only been a week, I have no/negligible drift - previously I had been tweaking the calibration feature and was not quite 100% on my timing. I unfortunately ordered a BGA package which was a PITA to solder - since I'm much more comfortable with through-hole, I might order a DIP version, make a quick board and clean up my installation a bit. Not the prettiest work, but it was quite simple:
1) I desoldered and removed crystal Q1 and the 22pf capacitors C8 & C9
2) Soldered wire to the 32kHz pins of the DS32kHz (C4,C5,D4,D5 - sorry don't know how to designate pins on BGA)
3) Soldered the other end of #2 to pin 9 of the ATMega
4) Soldered wire to the Vcc pins of the DS32kHz (C2,C3,D2,D3)
5) Soldered wire from #4 to a power pin (just past diode D2)
6) Soldered wire to the GND pins of the DS32kHz
7) Soldered wire from #6 to the ground pins for capacitors C8 & C9

I haven't wired up the battery backup yet - I'm trying to find a clean way to get to the battery (plus I got lazy and decided to quit while I was ahead.)
Here's the results:

Clock Mod with Maxim DS32kHz floating below the 08 and 12

MyClock.jpg (102.74 KiB) Viewed 3548 times

[kero905]

Awesome! That's some nice BGA soldering. I like the simplicity of your solution. I am using an I2C RTC for the Ice Tube Clock but that took a lot of code writing. I had not thought about getting a better xtal to replace the included one.

[adafruit]

nice work! it should be ultra precise, eh?

[revnull]

Hi, did you ever finish wiring the battery backup for your DS32khz? If so, do you have any more pictures of your mod. This seems much easier and more compact than using the DS3231/chronodot.
Although it would be nice to see a firmware port that used the DS3231 for both time keeping and temperature display. I guess I better starting reading & learning.

[revnull]

Since this was bikegeek's one and only post in the this forum I think he may never answer my question.
I've ordered some samples from Maxim in all 3 available packages to see which would fit best given the limited space in the case.



The operating temperature is normally 0c to +70c. The "-N" part number is the industrial version with an operating temperature of -40c to +85c (maybe useful if you leave your clock in the garage in the winter). On the upper left I have 2 EDIP pin-through versions. The upper right is the BGA version bikegeek used in his mod. The 2 on the bottom are the SOIC versions.



The PDF shows there are only 4 pins used in each package. If one was so inclined to use the BGA or SOIC packages, you could clip the extra pins to make soldering a little easier.

To keep soldering and placement nice and clean, where is the "best" place to tap into the battery? I assume I can just tag a wire directly the side of the coin cell holder. Also, would placing the chip in heat shrink (to prevent shorts) mess with the temperature compensation of the DS32khz?

[ortsac]

Just curious....what was your first mod on the Ice Tube Clock?

[revnull]

Well, after longer than a year, I finally got around to trying this mod.


I started by removing the crystal and 2 tuning caps:


I tried the SOC package first, but could not get it to work (maybe because I clipped all of the NC legs instead of grounding them). I opted for the next easiest to solder, the EDIP package.


I was able to tap the voltage regulator for the 5V Vcc (Red) line. Ground (Black) from the C9 ground hole. The Vbat (Also Red) line I tapped directly from the side of the battery holder. The 32kHz (Green) went to the crystal hole on the right.


Different vantage point:


Even though I believe I have everything hooked up properly, I still have 2 issues.
1. The clock keeps great time when externally powered, but when I remove the plug to simulate a power failure time freezes. I've checked all voltages (Vcc/Vbat) in both powered and non-powered states, everything is as it should be, but no joy.
2. I can not get the clock to work using an atmega328p. The tube lights and I can cycle menus, but time does not advance. The 328p worked fine with the crystal and caps in place.

If anyone can help shed light on either of these 2 problems, please let me know.

[jarchie]

I managed to get this hack to play nice with the 328p and sleep.

On the DS32kHz, the Vcc, GND, and all N.C. pins are wired to ground. The Vbat pin is connected to system power, which is 5 volts under regulated external power and around 3 volts on battery. The 32kHz output is connected directly to the ATmega328p XTAL1 pin.

On the firmware side, the code needed to use an external clock instead of a crystal oscillator. Specifically, the line that sets ASSR needed to be changed from

Code: Select all

ASSR |= _BV(AS2); // use crystal


to

Code: Select all

ASSR |= _BV(AS2) | _BV(EXCLK); // use external clock


Hope that helps! Also, I'd like to publically thank revnull; he sent me the DS32kHz to play with.

[revnull]

On the firmware side, the code needed to use an external clock instead of a crystal oscillator. Specifically, the line that sets ASSR needed to be changed from

Code: Select all

ASSR |= _BV(AS2); // use crystal


to

Code: Select all

ASSR |= _BV(AS2) | _BV(EXCLK); // use external clock


It works like a charm John! Thanks for looking into this. I think I'm going to try to hook up the much smaller SOC package in single power supply mode to my Icetube tonight. I'll then move my DIP to my monochron.

Final pictures to follow.

[jarchie]

I ended up installing the easily-soldered EDIP package, and glued it to the coin-cell holder with marine silicon. Even with the larger package, I don't think the DS32kHz detracts too much from the aesthetics of the clock, but judge for yourself:






For this configuration, I removed the clock crystal and caps (Q1, C8, and C9) and connected the DS32kHz installed as shown:





The datasheet for DS32kHz claims an error of less than one minute per year. I suspect that the accuracy can be increased further with software drift correction to address systematic error, but time will tell.

[Kavett]

Would I have to flash a new rom or is this a drop in replacement? I'm interested as the chronodot doesn't mesh well with the aesthetics of the clock and looks more complicated. I'm good with hardware but terrible with software so i haven't learned arduino yet. Thanks for the assist

[jarchie]

Based on bikegeek's and revnull's observations, the DS32kHz seems to work as a drop-in replacement with the ATMEGA chip that comes with the Ice Tube Clock kit, but most likely, the clock will fail to keep time on power failure. For the DS32kHz to work well, I believe you will need a reprogrammed chip.

If you'd like to learn to reprogram chips, there are people on this forum, including myself, who would be happy to help.

If you'd rather spend your free time on other pursuits, I would be willing to send you a reprogrammed chip if you will reimburse my expenses. If you're in the US, that would be $10 (~$3 for the chip, ~$2 for overhead, and ~$5 for USPS Priority Mail shipping). If you're interested, email me to work out the details.

[jarchie]

Although it would be nice to see a firmware port that used the DS3231 for both time keeping and temperature display. --revnull

If anyone is interested in using the DS3231, wd6cmu has posted his code, but noted that the temperature display seems too high. I've noticed the same thing; the clock seems to generate enough heat to raise internal temperature by five degrees or so.

Just curious....what was your first mod on the Ice Tube Clock? --ortsac

I see a photoresister installed in bikegeek's clock and suspect his first mod was the automatic dimmer mod.