Contact mode causes a tingle with low frequencies, but you will not feel anything when the frequencies are high enough.
Test with a sine wave frequency lower than 1000 Hz. "Backache 2" is a good example. Set the Frequency Limits boxes to zero. Uncheck the "Reduce amplitude < 10 KHz" check box. Set the amplitude to 10 volts. When you run the program, you should feel something between a slight tingle and a jolt. Adjust the amplitude up or down as desired.
Once you know that contact mode is working, you can use any frequencies that you want. It's a good idea to check the "Reduce amplitude < 10 KHz" checkbox for contact mode.
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