03-05-2015, 08:18 PM
Thinking about it I wouldn't drive the relay directly from the 555. Try disconnecting the relay and try again. If the circuit then works correctly you'd be better using a transistor to drive the relay.
However I've just checked the Signetics 555/556 handbook and they have a circuit driving a relay directly from the IC BUT there is a an extra diode between pin 3 and the relay, anode to pin 3 cathode to the relay and the option of a capacitor (value not specified) across the relay. As you've done the PCB I'd suggest trying the extra diode and if necessary a cap of say 10nF.
Keith
PS See you at NVCF next Sunday?
However I've just checked the Signetics 555/556 handbook and they have a circuit driving a relay directly from the IC BUT there is a an extra diode between pin 3 and the relay, anode to pin 3 cathode to the relay and the option of a capacitor (value not specified) across the relay. As you've done the PCB I'd suggest trying the extra diode and if necessary a cap of say 10nF.
Keith
PS See you at NVCF next Sunday?
