problem with 7474 bistable

[jayxflash]

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 ?

 

[davorin]

1. Do you have 5V supply for the 7474? Asuming yes if you followed the schematic (o;

2. Is the LED blinking when you press your remote control?

3. If so..is there a signal coming out of the 555? And you also see it at pin3 of 7474?

 

[golfbumb]

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].

Download https://focus.ti.com/lit/ds/symlink/cd74ac74.pdf for a datasheet. (Fairchild and National Semi datasheets state the same thing.)

 

[jayxflash]

ok guys, that was the problem, those 2 pins had to connect to Vcc not to GND. now it works just fine. thanks for help!