On Sat, Feb 5, 2011 at 6:29 AM, V G wrote: > As the final stage of the ECG, I want to build a voltage shifter to shift > the signal into the 0 to 5V range (my analog circuit operates in the -3.6= to > +3.6V range). Looking at the circuit at the bottom of the page here: > http://tinyurl.com/4tyjaho I have a few questions. > > 1. Is the first opamp (acting as a buffered output) really necessary? Wha= t > is its function? Why can't we just take the output from the voltage divid= er > directly? > > 2. Is the LM324 buffered? I can't find the answer to this anywhere. > > 3. The two input resistors are 1M ohms. This is a very high impedance. Wh= y > have they chosen this value? > > 4. The the gain setting resistors on the second opamp are 220K each, > designed to give the opamp a gain of 2. Do they really need to be 220K ea= ch? > Or can I just use something like 1K each instead? What difference does it > make, as long as the ratio is the same? > I also ran a SPICE simulation of the circuit. So far, it looks good: http://img64.imageshack.us/img64/4366/capturedv.png --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .