A hot wire thermocutter for polystyrene can be designed using electronic diagram shown below
To function properly the wire must be kept at a correct constant temperature, otherwise either not cut or burn the material and create blackened craters. A low voltage transformer capable of generating a current of 2 A is sufficient for circuit. By adjusting the current through the wire its temperature can be controlled. To reduce current consumption and power dissipation is intermittently interrupted by a triac.
One end of the line (represented in the scheme by RL) is directly connected to the transformer secondary winding. N1 and N2 turn transformer secondary voltage of a rectangular voltage.
N3 with surrounding components form a triac switch command timed. Time is determined by C3. This capacitor is charged via P1 and discharged through R5 and D3. Loading levels of C3 are the limits of the Schmitt trigger threshold levels N3. It follows that the voltage on C3 will be logic "1" or logic "0".
With a logic 1 N3 receives a positive impulse from N2, resulting in a short negative pulse at the output.
Also cause negative impulse voltage drop across the capacitor C3 in the N3's Tipping. This cycle can be adjusted in length by means of P1.
N3 will not react to impulses from the N2, so its output remains logic "1". C3 can not download the R5 and D3, and so the triac will be blocked. After a time (set by P1) C3 voltage is again logical "1" and the process repeats. R6 and C4 have the role to maintain the triac conduction throughout a period of AC power. Resistance wire used must not exceed 5 ohms.