After assembly of the kit according to the instructions, this is what I have found. The clock passed all tests during construction with good readings, and appeared to work well with nice evenly lit digits and everything (day date etc.) programmed properly. When I unplugged the clock to move it from my garage workbench to my desk it did not keep time and I had to reset it.
This seems to be an issue and there is discussion in various threads here in the clock forum about the icetube clock not keeping time when unplugged. Since it happened to my clock as wel I thought I would try to find out why when the clock is unplugged to move it to another location or the power goes out the clock does not keep time while on battery backup.
The FET Q3 is designed into the clock as a high side switch to disconnect the voltage from the tube filament (bias) and the voltage (VCC) from the MAX6921 VFD drive chip in the event of a loss of normal input voltage. This leaves only the ATmega168V-10PU processor powered by the battery and a good battery can power the processor for at least a couple weeks.
The Q3 FET will still work if it is installed backwards, so the clock will still work and display time just fine. Due to how a FET is constructed, the FET will not fully turn off if it is reversed in the circuit and will still pass current.
So, if the clock does not keep time while only on battery power then the FET Q3 is probably installed backwards causing it to not turn off properly when power is removed.
I have found that the current ZVP3306A (from Diodes Inc.) p-channel enhancement mode FET supplied for Q3 has the correct orientation when installed with the rounded side with writing on it facing the rounded side of the silkscreen outline on the board as in the photo below. This orientation also matches the schematic for the clock.
This is contrary to the assembly instructions which state:
Do this to check to see if Q3 is backwards:The transistor must be placed correctly if the MOSFET has the text on the flat side of the transistor make sure the rounded half of the transistor case matches the rounded silkscreen.
If the MOSFET has the text on the rounded side, flip it around so the text is facing away from the big capacitor and facing the 22 ohm resistor you just placed.
Caution! Up to 60 volts is present in parts of the clock while powered from the adapter. This test does not require the adapter to be plugged in.
1.) Unplug the clock from power and disassemble the case leaving the bottom plastic piece attached to the main board. Leave the tube installed in the female connector.
2.) Make sure the battery is fresh and not exhausted, or insert a new fresh battery into the battery holder.
3.) While the clock is unplugged and on battery only, check the voltage from ground (use the big tab of IC3 for ground) to Q3 FETs upper led that is located closest to the boards edge. See photo below for reference. This is the led that sends power to the VFD chip and the 22 ohm tube bias resistor R3. There should be zero volts on this led while on battery.
4.) If you get a voltage reading (I measured 2.1 volts, but this may vary some due to actual battery condition, part, and meter tolerances) then the Q3 FET is installed backwards or is damaged in some way.
To fix the issue:
1.) If the FET is installed backwards, remove the battery and then desolder Q3 and remove it from the board. Be careful not to overheat the FET when desoldering it or it will be damaged and no longer work. A good way to remove the FET is If there is enough led length left on Q3 (probably is), you can clip the leds flush with the top of the board and desolder the little pieces left from their holes using any desired method without worrying about damaging the FET.
2.) Turn Q3 around so the rounded side of the FET matches the silk screen as shown in the photo below and solder it back in.
3.) Insert the battery in its holder and measure the upper pin closest to the board edge to ground (big tab on IC3) again. There should now be zero volts on the led closest to the edge of the board.
4.) If you still get a voltage reading after turning the FET around, then the Q3 FET has likely been damaged by heat or static and needs to be replaced. Install the replacement FET in the new correct orientation of rounded side matching the printed silkscreens rounded side as the photo shows.
- ZVP3306A FET Q3 Correct orientation according to the ZVP3306A FET data sheet and the schematic of the clock. The led closest to board edge is the FETs Drain and the pad it is soldered to supplies the load when the FET is on. The source is the pin farthest from the board edge and is that pad is connected to the VCC source. The Gate is the middle pin and is connected to the processor.
- icetube_Q3_small.jpg (38.18 KiB) Viewed 2971 times
ZVP3306A FET Part link: http://www.digikey.com/product-detail/e ... 25?cur=USD
Datasheet: http://www.diodes.com/datasheets/ZVP3306A.pdf
Eagle files, board, and schematic: https://github.com/adafruit/Ice-Tube-Clock
Board assembly: http://learn.adafruit.com/ice-tube-cloc ... d-assembly
Another builders FET installed correctly (scroll to last photo): http://forums.adafruit.com/viewtopic.ph ... hm#p203372
And now......
Some helpful tips on clock assembly:
The Ice Cube Clock will blink the display after a power loss. This is normal and acts like most other commercial clocks to warn of a potential time loss due to a power loss. Toggle through the Menu options to stop the blinking.
- This how it's supposed to work anytime the clock senses a loss of power and is not an indication of the FET being installed backwards or some other problem.
The clock when first built and powered on has the brightness defaulted (is set) to the dimmest setting making it very hard to see
to set in normal room brightness.
The Brightness setting is the 4th menu in. Press the Menu button 4 times, then press the + button 2 or 3 times to set brightness higher
before trying to set other options. This makes it much easier to read the clock while initially setting and getting used to the menus and can be adjusted later as desired.
When installing the buttons on the board, make sure to get all of the buttons flat to the circuit board and keep them flat while soldering them in place. If the buttons are not flat to the circuit board, their black stems won't fit properly through the case holes and may stick in when pressed, so pay close attention to that detail. If they do get soldered in not quite flat then you may need to make the button holes in the case back slightly larger. Use care, the proper size drill bit (one size larger than the hole is good) in a battery drill, go slow and drill from both sides of the hole or the plastic may break.
Allow plenty of time to fit the tube to the circuit board it mounts on and be patient.
Tweezers and a small pair of needle nose pliers can help straighten any wires and assist in getting them through the holes.
Don't try to force any wires through their holes.
Inserting each wire a little ways into its corresponding hole, then bending the wires end over so it will stay in the hole
makes it easier to maneuver the tube and board while inserting wires.
Once all the wires are in their proper holes, begin moving the PC board up the wires toward the tube end. Use fingers, tweezers,
and needle nose pliers as necessary to assist in sliding the PC board into proper position.
And finally....
For those who wish to experiment with a FET:
For those who wish to experiment with a FET and the effects of installing it different ways, you can breadboard a quick demonstration. Insert a ZVP3306A (or a ZVP2120A) into a breadboard, connect the Source side led (see data sheet for pinout) of the FET to +5volts, connect the Drain side of the FET to the positive side of a LED, and then connect the negative (shorter led) side of the LED to a 560 ohm (or so) resistor, connect the other end of the resistor to ground. Now connect the Gate (middle led) on the FET to ground and the LED will light. Connect the Gate to +5v and the led will turn off. This is how a p-channel FET works. Now remove the FET from the breadboard, turn it around and place it back in the breadboard. This will reverse the Source and Drain connections with the drain now connected to +5volts and the source connected to the load (the LED). Now you will see that the LED lights up when the FET is inserted in the breadboard and is not quite as bright as before. This is because even though the FET is off the FET is still passing some current, though we did not tell it to do so. Now connect the Gate to ground and if you look closely when you do this you will see the LED get a bit brighter as the FET actually turns on. Connect the Gate to +5volts, the FET will turn off but the light will stay on, but get slightly dimmer as the FETs body diode is still conducting and the forward voltage drop makes the led slightly dimmer This can be used to an advantage in some circuits, but is not what we want for the clock.
