"The first section (U1B) of the LM358 dual op-amp is a 54 (2 x 27 Volts peak per cycle) volt peak-to-peak square wave oscillator. The second section (U1A) reverses polarity and provides ±27 Volts DC output of low impedance. This delivers a Bi-Phasic, sharp rise--time output of ~4 Hz"
" U1A, the second comparator, is used to invert the output of oscillator U1B. A ~54 Volt peak-to-peak signal will be generated between the op-amps due to their outputs being 180º out-of-phase. U1A's current is limited by potentiometer R5 (100 k Ohm) and R7 (820 Ohm)"