Power supply isolation

[sgergo]

Hi

I'm working on a simple 3 lead ECG design. The power supply would be plain simple 9V wall power supply. The design consist of an ECG amp stage, a PIC and a small wireless module. The ECG stage and the PIC are on 5V DC, the wireless module needs 3.3V, so I've got a simple ua7805 producing 5V from 9V and a TLV70033 making 3.3V from 5V.

I'd like to isolate the design galvanically but I'm stucked finding the appropiate info. I guess I should isolate between the 9V input - ua7805. It would be much appreciated if anybody would point me the right direction. Thank you.

 

[Electro_Nic]

Personnaly, i would isolate the ECG measurement chain. Is the ADC in the PIC ?
Option 1 : If so, then isolate between PIC and wireless module.
Option 2 : If not, isolate between ADC and PIC.

Example Option 1:
Get an isolated DC/DC supply on the board instead of TLV70033. Seperate the ground of the board and the isolated 3.3V ground (let's call this Ground_iso).
Then, every digital line going form the PIC to the wireless module and inversely, must be isolated. Use optoisolators for this. Or, use these little devices IL712, IL715 or IL716...
Remember, the two grounds cannot ever touch eachother... and make sure Optos are fast enough to pass the BW of the digital signals you are using.

Ciao for now,
Electro_Nic

 

[sgergo]

Hi Electro_Nic,

my apologies for the late reply. Thank you for your input.

Huhh...I am not sure I described my problem well or I used 'isolate' in a wrong context. I meant that for safety reasons I need to galvanically isolate the circuit to prevent electric shock in case of any malfunction.