Hello,

I am using 8051 in my project. My project consists of digital and analog part. I have made two different supplies for analog and digital +5V using different windings of the transformer. I am using a A/D converter (ICL7135) to convert analog signal to digital form. I am using a large number of digital IC\'s like 8031, 8255, 8279, 7404\'s ICL232, RTC, RAM , EEPROM etc. I have used 0.1 micro farad capacitors on every IC\'s. Now I have the following problems:

1) The digital grounds show 30mV signal from the source i.e. the power supply digital ground to the ground of 8031. How can this be avoided. Does this cause any harm?
2) Where and how should I join the analog ground to the digital ground?
3) During the conversion of analog to digital signal using the ICL7135, I observe that there is a variation of 2 to 3 mV\'s. Can it be because the digital and analog grounds are not joined at the right places. How can this be avoided? Also, The circuit shows around 50mV\'s between the digital and analog grounds.

Regards,

Mohit