# Add a floating voltage

Discussion in 'General Electronics Chat' started by DedeHai, Jan 27, 2009.

1. ### DedeHai Thread Starter Active Member

Jan 22, 2009
39
0
Hi everyone

I have circuit, giving out two measurement voltages. One ranges from 0-5V, the other one from 0-200mV. I need to transmit these two voltages over only 3 cables, so i want to create two voltage levels: v1 = 0-5V and v2 = v1+(0 - 200mV). At the other end of the line I get the v1 referenced to ground and the second voltage as a differential (v2 -v1).
First Idea was to use a voltage-adder opamp circuit, but the problem is, that the second voltage (0-200mv) is floating and not referenced to ground. So how can i add these two voltages?

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Voltages are relative. The only way to work with separate voltages is to make them common at some point. Does anything prevent you tying the floating voltage to the 5 volt ground?

3. ### DedeHai Thread Starter Active Member

Jan 22, 2009
39
0
I think the solution just came to me. I actually CAN reference the floating voltage to ground, by shifting a few components around.
Thanks for starting me off