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Black Star 4503 GPIB DMM Firmware Question
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DinoDubroja:
Hey, Im a little late to the party but if you are still here would you mind helping me out a bit. So i just repalced NiMh battery and powered it on with calibration key inside. How do i tell it to recall stored calibration constants? What do i have to do? I guess it is necessary to connect RS-232 to do this? Thanks!!
edpalmer42:
When you turn it on with the plug inserted, it automatically tries to repair the calibration constants.  You don't have to do anything. 

Since you replaced the battery, you've probably lost everything because the constants are only held in RAM.  No battery = no data.

Your only option at this point is to work your way through the calibration procedure in the manual.

AFAIK, there's no way to backup the constants before a battery swap.  That's an unfortunate gap in the meter's design.

Actually, the battery backup is a sloppy design to begin with.  Since you've already lost the data, now would be a good time to update the circuit.  The battery voltage is only 2V4 and there's a diode in series between the battery and the RAM chip.  That puts the RAM voltage too close to the minimum value even when the battery is fully charged.  Revising that circuit is somewhere on my list of future projects.  My plan is to increase the battery voltage to 3V6 and adjust the charging circuit to match.


Ed
AVGresponding:
At least they are easy to calibrate!

I ghetto-fabbed a two cell AAA pack into mine, but I like your idea; would suit a LiFePO4 cell quite well I think. As luck would have it I recently came into possession of a fair number of new (other) 18730s...
edpalmer42:

--- Quote from: AVGresponding on September 05, 2023, 08:43:56 pm ---At least they are easy to calibrate!

I ghetto-fabbed a two cell AAA pack into mine, but I like your idea; would suit a LiFePO4 cell quite well I think. As luck would have it I recently came into possession of a fair number of new (other) 18730s...

--- End quote ---

Somehow an 18730 LiFePO4 cell as a backup battery seems to be a serious case of overkill.  However, I totally support the idea of using what you've got.  My plan is to use a Varta Mempac 3V6 110mah battery.  I ended up with a tray of them a while back.  They're NiMH batteries that are designed for memory backup.

I like your AAA pack idea.  If you used non-rechargeable Lithium cells, they'd provide about 3 volts and they'd last almost forever - basically the shelf life of the batteries.

Ed
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