Power on delay with 555

Thread Starter

Franco_oz

Joined Jan 12, 2009
60
I am trying to build a circuit to delay a relay of about 30sec. Idea is to receive a trig signal and switch relay on after a set amount of secs (about 30). I thought was possible to achive it with a 555 but all my attempts failed. Any suggestion?
 

eblc1388

Joined Nov 28, 2008
1,543
You'll need to describe your problem more precisely.

Do you want to relay to operate 30 seconds regardless after a trip signal is initiated or do you want it ONLY to operate if the trip signal remains stable for 30 second?

How long would the relay output be? Fixed time or until trip signal reset?

What is the signal? Voltage or contact closure?
 

Thread Starter

Franco_oz

Joined Jan 12, 2009
60
Hi Eblc, no i need to switch the relay ON after about 30sec since the signal is received. signal is a contact closure. Hi Mik, i tried it but it doesnt work. I didnt actually build the circuit, just tried it in LTSpice.
 

mik3

Joined Feb 4, 2008
4,846
If you post your circuit it would be helpful. What problems did you face?
 

eblc1388

Joined Nov 28, 2008
1,543
Hi Eblc, no i need to switch the relay ON after about 30sec since the signal is received. signal is a contact closure. Hi Mik, i tried it but it doesnt work. I didnt actually build the circuit, just tried it in LTSpice.
1. A contact closes at t=0
2. A relay operates after 30 seconds (i.e. at t=30s)

Does the contact reset? Before or after 30 seconds?

Does the relay resets? For how long?

Edited: In many cases, a simple timing diagram will save all the troubles of asking those questions. An example is shown.

 

Attachments

Last edited:

mik3

Joined Feb 4, 2008
4,846
I can't open the file. Take a snap shot of the Spice window with the circuit in by using the print screen key on the keyboard and post it here as a jpg picture.
 

mik3

Joined Feb 4, 2008
4,846
First, for relay 3 to work you need to remove C9 from the circuit. Also, remove R10, it is not necessary, it juts waste power. What is the purpose of the last 555? What do you want it to do?
 

Thread Starter

Franco_oz

Joined Jan 12, 2009
60
R10 is to simulate relay coil. I made a mistake with net naming and RLY3 is supposed to drive the last 555 which in turns should wait about 30sec before close last relay (R12). That is my problem, i can't get the last 555 to work as i thought it should. From an application note from Philips, you can use the 555 as a "delayed ON" where the monostable don't change the output until timer runs out.
On http://home.cogeco.ca/~rpaisley4/LM555.html#29 example 20 shows similar circuitry but i can't get it to work.
 

Thread Starter

Franco_oz

Joined Jan 12, 2009
60
Heck Eblc, yes that is what i need! Dont give me the schematic, i want to understand what i am doing wrong....
 

Thread Starter

Franco_oz

Joined Jan 12, 2009
60
ok this is the output i get and i assume i am doing something wrong with the trigger? Fact you got it running in no time shows me i am doing some very stupid mistake but i can't figure out what! May need some help here.
Here is the updated schematic and its outputs. Also, how can you save waveforms on LTSpice?
 

Attachments

mik3

Joined Feb 4, 2008
4,846
Mik3 is here!;) Do you want the output of the last 555 to stay on for ever after the turn on delay?
 

Thread Starter

Franco_oz

Joined Jan 12, 2009
60
I need some hint here..... have checked and checked and can't work out the problem. Hate it!
 

Thread Starter

Franco_oz

Joined Jan 12, 2009
60
Yes that is the idea.... but as said before..... it doesn't. What am i doing wrong?
 
Top