I have a 7474 configured as bistable, and I don;t know why the circuit is not working. the scheme is presented here: **broken link removed** , everything is ok, the 555 works correct, but whatever signal is entered in 7474, the circuit is not working. in my opinion the circuit diagram is not wrong. any ideas ?
Actually, the schematic appears to be wrong. In the circuit, Preset-not and Clear-not of the 74LS74 are wired low. According to the 74LS74 data sheet, that is an unstable configuration that will forever output logic high on both Q and Qnot, regardless of clock activity. Wire preset and clear to logic high if you want it to operate as a multivibrator. If it still does not work then double check your VCC (pin 14) and ground (pin 7) [for a 14 pin device].