* Weighted summer

* Use parameters to set resistor values:
* (change these to match your experiment)
.param r1=20k
.param r2=10k
.param rf=20k

* Import the op amp subcircuit:
.include models/ua741.md

* Op amps need power supplies:
VDD ndd 0 DC 15V
VSS nss 0 DC -15V

* Next, the input voltages:
V1 n1 0 DC 1V
V2 n2 0 AC 1 SIN ({VO} {VA} {freq})

* Then the resistor network:
R1 n1 nn {r1}
R2 nc nn {r2}
RF nout nn {rf}

C1 n2 nc 10nF

* Finally, place the op amp:
*  non-inverting input
*    |  inverting input
*    |  |  positive power supply
*    |  |  |  negative power supply
*    |  |  |  |    output
*    |  |  |  |    |      model type
*    |  |  |  |    |      |
X1   0 nn ndd nss nout    ua741