[time-nuts] Oncore batteries

[Morris Odell]

> From: Matthew Smith <matt at smiffytech.com>
> Subject: Re: [time-nuts] Oncore batteries
>> Don't pull off the batteries! The boards are populated differently for
>> battery/non-battery uses. Your external battery will not be connected to 
>> the
>> onboard RAM.
>
> Too late - at least for the 'stuck' unit, although I haven't powered it
> with anything connected to the battery pin.

<snip>

> What I'd be interested to know is whether the Oncores CAN be run without
> the backup battery.  As Randy says, TTFF is not a concern for me so I'd
> rather have a less complex system that can be restored to a known state
> simply by removing power.
>
I went through this quandary with the VP a few months ago and got lots of 
help from members of this list, thanks guys!!

Briefly the VP has an onboard rechargeable Lithium cell and there is a 
charging circuit to keep it topped up. The connection to pin 1 which is 
documented as the backup battery is actually open circuited. The batteries 
on the VPs I have used were either missing or dead. For timing applications 
where you don't care about TTFF you can get away with just running them as 
they are. Be aware that an old VP that has been on the shelf for a while 
might take a long tome to get going but that's another issue.

If you really want to have battery backup, either try to find a rechargeable 
solder-in Li cell or connect a schottky diode between the cell positive 
terminal and pin 1 of the connector so you can use an outboard conventional 
Li cell. The diode prevents the charging cct from trying to charge the 
non-rechargeable cell.

I found that the VP always starts up in binary mode which is fine for me as 
I designed the host system to communicate with it that way. I always thought 
you had to issue the @@Ci message with appropriate arguments & checksum to 
get it to communicate in NMEA 4800 baud but I've never tried it. I don't 
know whether that's a volatile setting or not.

Morris