Auto start 555 timer

238

06:17:14

A 555 timer that auto starts with power and shuts off with power still applied.

Is there anything particularly wrong with the design of this circuit? As in although it works is there any problem with it?

Thanks.

published 8 years ago

denirahmadani

8 years ago

zanini007

8 years ago

1st. The diode you used in series with the relay isn't needed, but want to protect against the inductive power of the relay, you should use it in pararel to the relay (reverse polarity) 2nd. No reason for a relay to just turn on a LED. They're more expensive than a transistor and way slower 3th: You can use two transistors like this to remove the relay: http://everycircuit.com/circuit/5098948715085824

razzle308

8 years ago

Hi. Thanks for commenting. I put the diode there not for the relay as is usual but because when unpowered the simulator shows current flowing through the relay coil back into the output of the 555 and to ground. The diode stopped this. It is -42mv though. The relay is the final load. The led is just for a visual feedback to the circuit.

razzle308

8 years ago

So here it is with just the usual induction diode.

razzle308

8 years ago

Ok.. I had to put the diode back in. without it the capacitor on the trigger doesn't drain and the circuit does not reset. preventing it from being triggered again.

BillyT

8 years ago

You don't really need the first resistor, and 555 specs say 1k to 1M for the resistors, consider reducing the capacitors by /10 and increasing the resistor sizes by x10

razzle308

8 years ago

Ok - Thanks Billy. I wondered about that resistor. So it seems other than some values the circuit is not going to self destruct? :-D

BillyT

8 years ago

Basically the circuit is ok. It doesn't like starting with the power switch on.

razzle308

8 years ago

No i noticed that. Strange.

rich11292000

8 years ago

Initial DC calculation causes improbable 555 output.

hurz

8 years ago

The 555 model is quite buggy in EC. Anyway I modified the relay to be a more realistic 12V and not 5V. To have a quick restart behaviour I added a discharge diode. http://everycircuit.com/circuit/6144939950080000

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.