simple video inverter for the ZX 81

The inverter must be connected before the TV modulator in the ZX81. Switch S1enables bypassing of the inverter when inversion of the picture is not required. The composite video signal is inverted by gate N1. Gates N2 and N3 separate the sync signal from the input: the sync signal is then available at the output of N3 at a level of 5 Vpp. The inverted video signal and amplified sync signal are then added again, resulting in an inverted video signal with the sync signal in the correct position and at the right level. Preset P1serves to adjust the contrast. 51b ASTEC- Modulator 5V 85416-1 simple video inverter for ZX81 A J van Mil The circuit can be constructed on a piece of veroboard so small that it can easily be added in the ZX81 case. The power supply can be taken from IC1 in the ZX81: +5 V at pin 40 and earth (0V)atpin34. C>We" N1...N3=%ICI=74LS00 85416-2 video in C>. inverse video & sync. C> inverse video out 1C1 M1C EAR R34 C12 47pF USA ONLY ROMC.S Fn. ,1‘ .13 <.<< UK1 USA2...