Re: [Openeeg-list] Help - no calibration signal shown - possibly too low gain?

[Joerg H. <in...@jh...>]

Hi,

Robert Mayster, 29.10.2008 23:56 :
> Hi Joerg,
> 
> thanks a lot for your help - I shorted the resistors one by one like you 
> described and it looks like there is really a problem with the calibration 
> circuitry (probably the easiest part of the whole soldering - d'oh!)
> I checked my scope - although it isn't too well calibrated i can safely 
> assume that the calibration signal I get from the board is about 25uV 
> instead of 250 uV.

Factor 10 too low?

Have a close look (visually or with a multimeter) at R240! Is it really 100 Ohms 
or more 10 Ohms?

If this is OK a 2nd candidate is R227 and R223 are not 1meg but 10meg.
Check this out too!

> I will now try to mock a 250uV signal with my function generator to see 
> whether this works better.

A function generator might be problematic if it is mains powered.

Regards,

	Joerg