Ltspice

Using a captured waveform as LTspice input

This outlines the steps necessary to use a CSV file as input for LTspice.

Capture your waveform

I have captured the following waveform using my scope, and saved it as a CSV file.

A sample of the CSV file is shown below:

x-axis,3,D0-D7
second,Volt,
-1.0000000E-03,-48.2407212E-03,0
-999.8000E-06,-48.2407212E-03,0
-999.6000E-06,-48.2407212E-03,0
-999.4000E-06,-48.2407212E-03,0
- - - - - - - - >8 - - - - - - - -
+8.9990000E-03,-168.8437350E-03,0
+8.9992000E-03,-176.8839359E-03,0
+8.9994000E-03,-48.2407212E-03,0
+8.9996000E-03,-48.2407212E-03,0

Convert the CSV file to a RAW 8-bit file

Use the following script below.

#!/bin/bash -e
 
CSV_FILE=loaded.csv
CSV_COLUMN=2
 
ROOT_FILENAME=$(echo ${CSV_FILE} | rev | cut -d . -f 2- | rev)
 
# end of configuration
 
cat ${CSV_FILE} \
  | tail -n+3 \
  | cut -d , -f ${CSV_COLUMN} \
  | sed -r \
    -e 's/^\+//' \
    -e 's/^(-?[0-9]+\.[0-9]+)[eE]([+-])([0-9]+)$/\1*(10^\2\3)/' \
    -e 's/\*\(10\^\+00\)$//' \
  | bc -l \
  | sed -re 's/^(-?)\./\10./' \
  | tee .${CSV_FILE}.normal \
  | sort -n \
  | uniq \
  > .${CSV_FILE}.sorted
 
cat .${CSV_FILE}.sorted | sed -n "1p;$(wc -l .${CSV_FILE}.sorted | cut -d ' ' -f 1)p" > .${CSV_FILE}.extremes
 
LO=$(cat .${CSV_FILE}.extremes | head -n 1)
if [ $(echo "${LO} < 0" | bc) == "1" ]; then
  OP=-
else
  OP=+
fi
HI=$(echo "($(cat .${CSV_FILE}.extremes | tail -n 1))${OP}(${LO})" | bc -l)
ML=$(echo "255/${HI}" | bc -l)
 
cat .${CSV_FILE}.normal \
  | sed -r \
    -e 's/^/((/' \
    -e 's/$/)/' \
    -e "s/$/${OP}(${LO})/" \
    -e "s/$/)*${ML}/" \
  | bc -l \
  | sed -r \
    -e 's/^([0-9]*).([0-9]?[0-9]?[0-9]?).*$/\1.\2/' \
  | tee .${CSV_FILE}.adjusted \
  | awk '{printf "%c", strtonum($0)}' \
  > ${ROOT_FILENAME}.raw