[Elecraft] [KPA500] Rear power switch thread

[Jack Smith]

It's also possible to power the micro-controller through a diode 
isolated super capacitor of 1 or 2 farads that will run it for some 
considerable time. The firmware would then detect un-planned power 
removal sequence and perform an appropriate save process before the 
super capacitor voltage drops below the brownout level.

I have a real-time clock in one of my PIC projects powered with a diode 
isolated 0.22 farad super capacitor that will run the RTC clock chip for 
several days if power is removed. That chip consumes much less power 
than a PIC, but it shouldn't take a PIC more than few hundred 
milliseconds to save variables to EEPROM.

Nice thing about the super capacitors is that unlike a battery they have 
essentially unlimited life. However, the discharge voltage follows the 
RC network rule, not like the more or less flat output from a battery.

Jack K8ZOA


On 12/1/2011 6:47 PM, ab2tc wrote:
> Hi all,
>
> Choosing EEPROM for nonvoatile storage was the right choice then and still
> is. Please don't even entertain a single thought about going back to a
> battery backed up RAM solution (remember PC BIOS settings in "CMOS"?). It
> has infinitely more problems than an EEPROM based solution. I really have no
> idea what people are complaining about. I don't think there are any products
> out there anymore relying on battery backed up CMOS RAM, thank God. There
> are many ways to improve (if improvements are indeed needed) the power loss
> reliability of non-volatile storage, such as fallback on a second copy
> should the first one fail (you do use checksums, right?)
>
> AB2TC - Knut
>
>
> wayne burdick wrote
>> The K3 (like the K2 and our other rigs) uses EEPROM for nonvolatile
>> parameter storage. This decision was based on several criteria, and we
>> believe it was the right choice at the time. It's conceivable that in
>> a future product we might go with battery-backed-up RAM.
>>
>> The MCU does try to write all changed parameters to EEPROM in the
>> event of power disappearing suddenly; the electrolytic capacitors do
>> hold up the MCU's voltage for some milliseconds. But your humble
>> firmware guy is a lot happier when power is turned off at the radio
>> first, allowing a clean shut-down sequence.
>>
>> Thanks for your tolerance of our various idiosyncrasies.
>>
>> 73,
>> Wayne
>> N6KR
>>
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