to the controller 1 the controller 1 can therefore switch through the ignition output stage 4 across the bi directional control line 5 whereupon the electric current through the ignition coil 3 increases in a largely linear manner as shown in fig2 on the output side the ignition coil 3 is connected across a diode 8 to a spark plug 9 so that when the ignition output stage 4 is blocked the ignition coil 3 can discharge across the spark plug 9 thereby generating an ignition spark a tap for voltage metering is provided between the ignition output stage 4 and the precision resistor 6 and is connected to a metering input of a comparator 10 the other input of the comparator is connected to a central tap of a voltage divider which comprises two resistors 11 12 whereby the size of the resistor 12 defines a reference current value for charging the ignition coil 3 on the output side the comparator 10 is connected to the base of a transistor 13 which connects the control input of the ignition device across a resistor 14 to earth and forms a controllable current sink when the transistor 13 is switched through the control input of the ignition device 2 is drawn to earth specifically across the resistor 14 so that the ignition device 2 draws an additional current from the controller across the bi directional connecting line and this can be identified by said controller the transistor 13 is switched through when the comparator 10 identifies that the electric current flowing through the ignition coil 3 exceeds the predefined reference current value the ignition device 2 also has a further controllable current sink which comprises a transistor 15 and an earthed resistor 16 whereby the.