Scale EEPROM?

[vlad777]

I disassembled two different (weight) scales from
two different manufacturers and apart from COB they
both contain 24C02 EEPROM.

What do you think is in these eeproms?

Many thanks.

[Len]

Calibration data? 

[mikeselectricstuff]

Calibration and probably also features - kg/pounds etc. the COB will be a mask rom, so having external ee allows the same one to be used for different models

[vlad777]

Could it be that the COB is uC and eeprom contains firmware?
(apart from calibration)

[tom66]

I would doubt it. Any firmware is basic enough to fit in mask memory. If there is any. A basic scale wouldn't need much more.

[vlad777]

What about calibration?
Is it programmed once or does the scale recal on it's own?

[mikeselectricstuff]

What about calibration?
Is it programmed once or does the scale recal on it's own?

it will be a factory cal to correct for cheap sensor  and electronics

[GreyWoolfe]

Back in New Jersey in the 80's when I worked for Nabisco as a salesman, I remember seeing the scales in he grocery stores with calibration stickers on them.  I seem to remember the scales had to checked for accuracy on a yearly basis.  Not sure though if the scales then were purely mechanical or had electronics in them.

[JoannaK]

What about calibration?
Is it programmed once or does the scale recal on it's own?

it will be a factory cal to correct for cheap sensor  and electronics

I have even seen some cheapish chinese kitchen scales that are user re-calibrable. Just add 1KG atop and press some button combination mentioned in manual.

[vlad777]

I have even seen some cheapish chinese kitchen scales that are user re-calibrable. Just add 1KG atop and press some button combination mentioned in manual.

Thanks,I didn't know that.
Sounds like a good idea.

[Zero999]

Calibration and probably also features - kg/pounds etc. the COB will be a mask rom, so having external ee allows the same one to be used for different models

I notice you've mentioned features. Do you mean it might be possible to hack it to a higher specification, like a Rigol 'scope?

[SeanB]

Typically the one chip solution is capable of working from 1kg to 300kg, depending on the load cell and mechanical base used around it. The ADC on there is typically a 14 bit unit, using digital smoothing and a lot of samples to get a stable reading. The eeprom will typically have a set of values for display type ( no of digits, decimal location, units and other annuciators), full scale resolution ( the load cell gives about the same raw digital reading from zero strain to max design strain), base count units ( the typical unit will do 5g intervals while the sensor result typically will be 2g5 or so but will drift a little), zero mass value (the unloaded mass of the weight platform and mechanical parts on the knife edges) and finally a scale value set ( one or more breakpoints) used to trim the conversion from digital ADC data to displayed data.

Typically you turn it on and level it, leave it to warm up for a hour or so then put it in cal mode ( can be a switch on the board, a button combo or a plug in dongle), zero it and then place a reference masspiece on and adjust the display to show the calibration mass. Some you do at multiple points to get the multipoint slope used to linearise the unit. I have one that requires a preset mass, so I have to use a combination of mass references to get the closest match, it is out by about 3mg then.