In essense, whatI have are four 555s (2x556) One is a 0.5 s monostable,the other a 147 Hz tone generator. The other is a (30 s) monostable, and a 0.3 s astable.
If I run the 0.3 s astable on its own, (disconnect diodes) it runs fine. I have the reset tied to ground via a relay coil which disables the astable. Place VCC on the high side of relay, and it is enabled as planned.
The other part of the circuit was originally a 30 s timer, but it would cut off after about 1.5 s despite a 150 kΩ and 470 uF cap.
So I changed the circuit a little so the threshold was grounded via 100 kΩ. Now when triggered, it should stay on indefinitely.
However, the problem arise trying to connect the two parts.
Again, my theory says that the high output of the monostable should power the relay and present a high to the reset pin.
That's when it chops off at 1.5 s. (Why it is 1.5 s when there are no timing components with that RC period is also a mystery; I have tried 4700 uF as a supply decouple, but it makes no difference.)
The GND to relay top is a protection diode, and the other was suggested to stop the circuit "locking up".
The relay is a FRS-1 with a coil value of 320 Ω.
(Maybe the reset is being pulled low? But I thought the top of the coil should be at the voltage of the 556 output)
** I have shown two 555's in diagram as there is no 556 on Circuit Lab. But the 556 IS two 555 chips anyway !