I'm trying to implement the following schematic of a simple analog computer
The inputs are x and y, according to the text where I found this diagram the circles represent voltage dividers or potentiometers.
There are some things I dont get, for instance the divider in the feedback loop is \$ \frac{1}{k}\$ and it also states that k is between 0 and 1, so that means that \$ \frac{1}{k}>1\$, that implies that the divider should actually be an amplifier instead?
This is how I implemented it:
simulate this circuit – Schematic created using CircuitLab
With the resistor values I selected for the circuit, a=b=0.5, and \$\frac{1}{k}=5\$, which means that the final equation is supposed to be \$-0.2(0.5x+5y) \$. However, if one analyzes the circuit using superposition, we have:
$$v_o=-(ax+10by+\frac{1}{k}v_o)$$
or
$$v_o=\frac{-k(ax+10by)}{k+1}$$
What am I doing wrong? how is the circuit supposed to be to in order to get the correct output \$v_o=-k(ax+10by)\$?
Best Answer
Your circuit is way too complicated. You need to study how an inverting gain op amp circuit works. Once you understand, the gain for voltage on the left side of R6 is -1 (-R3/R6) and the gain for voltage on left side of R2 is -10 (-R3/R2).
You can eliminate everything other than OA1, R3, R2 and R6. R2 and R6 will connect directly to Y and X power supplies.
The gain of the resulting circuit will be -R3/R6 * x + -R3/R2 * y.
Now rearrange original equation to -kax + -10bky.
R6 = R3/ka and R2 = R3/10bk