A circuit for unilaterally scanning teletype characters wherein the characters are supplied to an integrating circuit and to an impulse circuit wherein the impulse circuit can be controlled by the step changes of a character. A comparator circuit receives the output of the integration circuit and assumes a definite condition with each step change through a switch which is controlled by the impulses of the impulse circuit and a reference signal is supplied to the comparator circuit and the reference signal can be adjusted according to the desired delay of the descending or ascending edge of the step changes in the characters.