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By: Windell (offline) on Thursday, December 07 2006 @ 02:33 AM PST (Read 11912 times)  
Windell

This is the place to discuss tricks, tips, and troubles with the holiday electronics projects, whether you got a kit from us, you're building your own, or you're writing firmware for next year's model!

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By: Anonymous: Anonymous () on Monday, December 11 2006 @ 07:21 PM PST  
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Hello! I received my ornament kit today! I soldered everything up, but when I turned it on the LCD started blinking on and off really fast, and that's it. I checked all the connections with a multimeter and made extra sure nothing was shorting. Any idea what's up? Did I fry the chip while soldering maybe? Thanks! - Jason





       
   
By: Windell (offline) on Monday, December 11 2006 @ 08:05 PM PST  
Windell

Yikes-- That doesn't sound good! So long as you are seeing blinking, the chip is not dead or zapped by static-- if the chip goes, it will go all the way and no longer be able to blink for you at all. I have seen the blinking condition before, however I have not seen a case where it was not cured by letting it run for several seconds and/or cycling the power a few times. I suggest removing the batteries from the battery case and putting them back in. I also suspect that the power supply connection to the chip (from the battery box to pins 10 and 20) is not as solid as it should be-- see below for why I suspect that. So why is this happening? Each time that the microcontroller starts up, it checks to see what value is stored in EEPROM (nonvolatile memory), telling it which text string to display next. It then updates the value and stores the new one. The problem is that the EEPROM (nonvolatile memory) can be corrupted if the unit abruptly loses power during that write process. If that happens, the microcontroller will display some funny blinky junk the next time that it starts up, but the program is designed to automatically detect and correct this condition, so that it will work correctly the next time that power is applied to the chip. The EEPROM write process is a very short time window, so the only way that this can happen in practice is if the electrical connection from the chip to its power supply is intermittant-- dropping out every once in a while. The easiest way to get that is with a poor ("cold"Wink solder joint to one of the two power pins; it could still test okay with a multimeter but give dropouts, so please try resoldering the connections from the battery box to the two power pins of the chip. In any case, if it doesn't start behaving, send me e-mail, and I'll send you a new chip.---Windell H. Oskay drwho(at)evilmadscientist.com http://www.evilmadscientist.com/


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By: Anonymous: Anonymous () on Monday, December 11 2006 @ 08:24 PM PST  
Anonymous: Anonymous

Thanks Windell! I was afraid to just let it run because I thought something was wrong. I tried just leaving it on for a while and it cleared up after about 10 seconds. Now it's working fine - no more blinking!





       
   
By: Windell (offline) on Monday, December 11 2006 @ 08:28 PM PST  
Windell

Oh, good. I love it when things work correctly! ---Windell H. Oskay drwho(at)evilmadscientist.com http://www.evilmadscientist.com/


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By: Anonymous: Anonymous () on Wednesday, December 20 2006 @ 09:55 AM PST  
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Thanks for making these kits available. The ornament kit at least seems particular about voltage - it won't work with some of my NiMH cells (nominally 1.2 volts each). I had to cherry pick to get a pair that would supply a somewhat higher voltage. I recommend alkaline batteries. -Roy





       
   
By: Windell (offline) on Wednesday, December 20 2006 @ 11:17 AM PST  
Windell

They are designed to work with alkalines-- I'm surprised that they work with NiMHs at all! One of the features that the chip uses is brown-out detection. It checks to make sure that the battery voltage is above a certain level, 2.7 V, in order to turn on. That is to make sure that it doesn't try to write to the EEPROM when the voltage is too low. If your NiMHs are above (2.7 V)/2, they're pretty highly charged!---Windell H. Oskay drwho(at)evilmadscientist.com http://www.evilmadscientist.com/


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By: Anonymous: Anonymous () on Saturday, December 23 2006 @ 04:50 PM PST  
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Hi, the ornament kit is great. I made one yesterday and the second one about an hour ago. I'm going to give it up as a secret santa gift at a party later today :-). My question is, what battery life do you expect from two alky AA's? I think yesterday I got maybe 5hrs of blinkage.





       
   
By: Windell (offline) on Saturday, December 23 2006 @ 08:27 PM PST  
Windell

I tested one with a fresh set of batteries and got about five hours as well, which is actually a bit disappointing. There is necessarily a trade off between brighter and longer battery life, and these run pretty bright and not very long. For future kits I might be able to obtain more energy efficient LED displays, which would give longer battery life but raise the cost of the kits.---Windell H. Oskay drwho(at)evilmadscientist.com http://www.evilmadscientist.com/


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By: unrepentantgeek (offline) on Tuesday, December 26 2006 @ 02:12 AM PST  
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It would add complexity, but maybe the ornament could be powered off a light string? That's only 2.2-2.4V AC so it's a bit tricky, but there are some pretty interesting power management chips out there so maybe there's something available.


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By: Windell (offline) on Tuesday, December 26 2006 @ 03:20 AM PST  
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Certainly that's possible. In fact, you could make a whole strand of readerboard ornaments-- that might be easier than powering one. As a practical matter, it would necessarily raise the cost and complexity of the kits to put that power supply in place. Battery power is particularly clean and easy to use, and going to a plug-in power supply means that a certain amount of protection circuitry has to be added. If you're going from a higher DC voltage to a lower DC voltage, you can add a voltage regulator chip and two capacitors to do the job-- that's pretty easy, but already doubles the number of components that need to be soldered. If you want to power the ornament off of low-voltage AC instead, you're going from lower voltage to higher voltage and AC to DC, which means that quite a few other components are needed and it wouldn't make such a simple little kit anymore. The most practical means of powering these other than with a battery would be to use a wall wart followed by a switch and a little conditioning circuit consisiting of a voltage regulator, two capacitors, and an inductor. I might make that an option later, but I suspect that most people woud rather have the simpler kit, particularly if the battery life can be extended by a factor of 5-10 (meaning that it could be run for a few hours an evening for a week on one set of batteries) while keeping the display bright. Again, battery life versus brightness is a tradeoff. If you want to trade some of your brightness for battery life in one of the existing ornaments you can: Replace the one loose wire in the circuit by a small-value resistor, say 50-100 ohms, 1/4 W. It will not run as bright, but it will have a significant effect on battery life. ---Windell H. Oskay drwho(at)evilmadscientist.com http://www.evilmadscientist.com/


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By: Anonymous: Anonymous () on Thursday, December 28 2006 @ 12:49 PM PST  
Anonymous: Anonymous

Has anyone found a pin-compataible replacement for the PSA08-11HWA display, preferably available at Digikey or Mouser? I accidentically killed one of my segments (likely by shorting it to +V with a stray clipped-off component lead). Thanks, Roy





       
   
By: Windell (offline) on Thursday, December 28 2006 @ 01:05 PM PST  
Windell

There are several possibilities, but I don't know of any at Digi-key or Mouser. I've seen them at several non-mainstream electronics shops (like circuit specialists):

From the original article:
You can get a compatible but brighter version of the same display (the PSA08-11EWA) from Circuit Specialists for $3.72 each.

You can also always order more kits =).
(Seriously, though, if you place another order sometime, I can put in an extra display for an extra dollar.)

---
Windell H. Oskay
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By: Anonymous: Anonymous () on Thursday, December 28 2006 @ 01:22 PM PST  
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Thanks... I may take you up on that. I may also be playing around with wall-wart power later - will keep you posted. -Roy





       
   



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