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555 timer delay pulse output?

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WuNgUnSVT

New Member
I need some professional help!
I need a device to activate a latching relay...
I need it to ONLY function when an input signal (+ current from a push button) is on for a steady 2 seconds. After 2 seconds of holding the push button, I just need a pulse to activate the latch. This part is important...
Just a quick pulse...no steady output...

I've done a few hours of reading and Googling, but I can't find exactly what I need...

TIA
 

ericgibbs

Well-Known Member
Most Helpful Member
WuNgUnSVT said:
I need some professional help!
I need a device to activate a latching relay...
I need it to ONLY function when an input signal (+ current from a push button) is on for a steady 2 seconds. After 2 seconds of holding the push button, I just need a pulse to activate the latch. This part is important...
Just a quick pulse...no steady output...

I've done a few hours of reading and Googling, but I can't find exactly what I need...

TIA
hi,
Have a look at this drawing, get the 555 datasheet and work out the monostable pulse time required to latch the relay.

Use a 1M0 for VR1 and a 1uF for C1, adjust RV1 for a 2 sec 'trigger' delay.

This is just one of many ways to get the 2sec hold off delay...:rolleyes:

Is this clear.?
 
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WuNgUnSVT

New Member
I can follow it somewhat...the resistors, capacitors and diodes...
I see a variable resistors there as well...
I can make out the ground points...
Ummm, is that a Q1 near the center there? Dunno what that is...
The C1 and the C1 2N2...those are different schematic icons. Is one polarized maybe?

Maybe I don't need a pulse output. When the timer is reached, and the button still pushed, the power is sent to the relay...I assume once the button is released, the power is killed to the relay?
If so, then that's all I need...
 

ericgibbs

Well-Known Member
Most Helpful Member
WuNgUnSVT said:
I can follow it somewhat...the resistors, capacitors and diodes...
I see a variable resistors there as well...
I can make out the ground points...
Ummm, is that a Q1 near the center there? Dunno what that is...
The C1 and the C1 2N2...those are different schematic icons. Is one polarized maybe?

Maybe I don't need a pulse output. When the timer is reached, and the button still pushed, the power is sent to the relay...I assume once the button is released, the power is killed to the relay?
If so, then that's all I need...

Hi,
This is what your first post said.:rolleyes:

I need it to ONLY function when an input signal (+ current from a push button) is on for a steady 2 seconds. After 2 seconds of holding the push button, I just need a pulse to activate the latch. This part is important...
Just a quick pulse...no steady output...


Q1 is n channel FET, C1 is a polarised cap.

Maybe I don't need a pulse output

Let me know when you have decided....:confused:
 

ericgibbs

Well-Known Member
Most Helpful Member
hi,
This verison will give a 2sec on delay, the drive to the relay will remain on until you take your finger off the push button..
 
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WuNgUnSVT

New Member
ericgibbs said:
hi,
This verison will give a 2sec on delay, the drive to the relay will remain on until you take your finger off the push button..

That's it! Perfect...
My latch relay works by reversing the polarity on the coil to unlatch, so it would short something out if there wasn't a 'pulse' output from the timer and I went to unlatch it...

Thanks for your help!

Now I need to figure out how to send a + and - pulse to the latch from just a + signal. I'm thinking a relay hooked up to ground, triggered by the same + signal?
 
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ericgibbs

Well-Known Member
Most Helpful Member
WuNgUnSVT said:
That's it! Perfect...
My latch relay works by reversing the polarity on the coil to unlatch, so it would short something out if there wasn't a 'pulse' output from the timer and I went to unlatch it...

Thanks for your help!

If you reverse the coil voltage to unlatch it, dont forget to remove the clamp diode..:eek:

Use a 0.1uF and 47R [snubber] in series, paralled across the coil..
 

WuNgUnSVT

New Member
I found this...I think circuit 2 is similar to the one you posted here?
Would circuit 3 be better suited for activating a relay in which it can't have a constant ground attached to it, because of the reverse polarity unlatching...
I would just have to also send the + output to a grounded relay, to pulse a ground signal to the latch together with the +?

Ummmm...what is Q1 in this diagram anyhow? Does C1 control the amount of delay??
Thanks again

**broken link removed**
 

ericgibbs

Well-Known Member
Most Helpful Member
I found this...I think circuit 2 is similar to the one you posted here?
Would circuit 3 be better suited for activating a relay in which it can't have a constant ground attached to it, because of the reverse polarity unlatching...
I would just have to also send the + output to a grounded relay, to pulse a ground signal to the latch together with the +?

Ummmm...what is Q1 in this diagram anyhow? Does C1 control the amount of delay??


hi,
In these 3 circuits, the power is switched on continously after the timing period. I believe you required a single pulse at the end of the time out.?

Q1 is a n channel FET and C1 controls the switch on delay together with RV1.

Are you asking for details on how to apply the reverse polarity pulse to unlatch the relay.?
 

WuNgUnSVT

New Member
ericgibbs said:
I found this...I think circuit 2 is similar to the one you posted here?
Would circuit 3 be better suited for activating a relay in which it can't have a constant ground attached to it, because of the reverse polarity unlatching...
I would just have to also send the + output to a grounded relay, to pulse a ground signal to the latch together with the +?

Ummmm...what is Q1 in this diagram anyhow? Does C1 control the amount of delay??


hi,
In these 3 circuits, the power is switched on continously after the timing period. I believe you required a single pulse at the end of the time out.?

Q1 is a n channel FET and C1 controls the switch on delay together with RV1.

Are you asking for details on how to apply the reverse polarity pulse to unlatch the relay.?

I have a seperate switch to apply the unlatching signal to both + and - terminals of the relay...
Notice there isn't a switch in these diagrams...in my case, power will be applied from a switch...so I assume the output will cease once the switch is released?
 
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ericgibbs

Well-Known Member
Most Helpful Member
I have a seperate switch to apply the unlatching signal to both + and - terminals of the relay...
Notice there isn't a switch in these diagrams...in my case, power will be applied from a switch...so I assume the output will cease once the switch is released?


Are you saying there is a supply operating voltage to the 555 ONLY while the switch is pressed.??

What duration does the latch pulse have to be at the end of the 2secs, why do you need the 2sec delay.?
 

WuNgUnSVT

New Member
ericgibbs said:
I have a seperate switch to apply the unlatching signal to both + and - terminals of the relay...
Notice there isn't a switch in these diagrams...in my case, power will be applied from a switch...so I assume the output will cease once the switch is released?


Are you saying there is a supply operating voltage to the 555 ONLY while the switch is pressed.??

What duration does the latch pulse have to be at the end of the 2secs, why do you need the 2sec delay.?

That is correct...only when switched.
This whole setup is part of a push button car starter. The car starter is 'looking' for two pulses to trigger the start sequence. THIS layout is for powering on the ignition without starting the car.
The two second hold on the button is ignored by the car starter...it's only to pulse the latch relay, which in turn powers 2 Bosch relays...one for ignition, the other for accessory...
 

ericgibbs

Well-Known Member
Most Helpful Member
WuNgUnSVT said:
That is correct...only when switched.
This whole setup is part of a push button car starter. The car starter is 'looking' for two pulses to trigger the start sequence. THIS layout is for powering on the ignition without starting the car.
The two second hold on the button is ignored by the car starter...it's only to pulse the latch relay, which in turn powers 2 Bosch relays...one for ignition, the other for accessory...

As its a car, you would power the 555 from the car battery, via a simple regulator and apply the switch voltage to the top of the RV1 potentiometer.

I'll redraw the circuit,, I am closing down for today...
 

ericgibbs

Well-Known Member
Most Helpful Member
hi,
Look at this diagram.

The circuit is powered from the 12V car battery.

Pressing and holding down switch S1 will trigger the 555 monostable after a 2 second delay.
The 555 mono will output a pulse [ you must determine the values of RT and CT to suit the relay pulse latching time].

The 555 output drives a npn transistor which in turn drives the relay drive transistor.
As I dont know the details of the relay coil, you will have to choose a suitable PNP transistor.

One side of the relay coil is grounded as you suggested.

How do plan to apply a reverse polarity pulse to the relay.?

A two pole change over switch could be one way to do it..
 
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WuNgUnSVT

New Member
Jeezus...this is getting sophisticated! Definitely over my head, skill-wise...

Is there a voltage regulator on there too? I don't need that...I plan on using a 7805 seperately before it even gets to the circuit...
I marvel at your skills here, but I think this might be overkill?

I don't need an electronic pulse, per se, designed into this...
Yes, the relay itself needs a pulse to latch, but I can make do with a steady output as long as the switch is held. Once released, then no more output...this is perfectly fine, and simplier.
As for the output itself, all I need is just a + lead coming off the circuit...
I don't understand how the relay is integrated in your design here...
There is a LOT going on here I don't understand...
Isn't that design #3 sufficient for my purposes, minus the vreg?

I can take just a + output, run it to the + side of the latch, and run the same + lead into a grounded relay, to send a ground pulse to the latch at the same time...wouldn't that be easier? I can't have it constantly grounded, because of the polarity swap needed for unlatching...

As far as unlatching, I have another switch setup for this...which just applies opposite polarity to the relay to unlatch it...

Here is a pic of the parts...
**broken link removed**
 

ericgibbs

Well-Known Member
Most Helpful Member
hi,
There is no Vreg in any of the circuits.???

I would suggest that you post a diagram on how you see the project wired up, then I can suggest a way of meeting the requirement..;)
 

WuNgUnSVT

New Member
ericgibbs said:
hi,
There is no Vreg in any of the circuits.???

I would suggest that you post a diagram on how you see the project wired up, then I can suggest a way of meeting the requirement..;)

Yes...I plan on regulating the power going into the circuit with a 7805. I can easily add this to the board myself...

Have a look at circuit #2
Again, I'm unsure if the way the relay is hooked up (constant ground?) is what I need...

Circuit #3...looks like just a + output, which I can make work, like how I explained it in my last post. I just don't understand the theory with the transistors...

**broken link removed**
 

ericgibbs

Well-Known Member
Most Helpful Member
Yes...I plan on regulating the power going into the circuit with a 7805. I can easily add this to the board myself...

Have a look at circuit #2
Again, I'm unsure if the way the relay is hooked up (constant ground?) is what I need...

Circuit #3...looks like just a + output, which I can make work, like how I explained it in my last post. I just don't understand the theory with the transistors...


Hi,
Using circuit 1, 2, or 3 driven by 7805 Vreg +5V, would mean that the relay would have to a 5Vdc coil,,,, what voltage is the one you have.?

Can you post a specification of the relay and switch shown in the picture you posted.?

For Cct3 the Q1 transistor is switched ON, conducting, after the switch ON delay period has timed out, it will remain ON all the time while the power is switched on. Again with a 7805 Vreg the voltage will be under +5V from the transistor.
 

WuNgUnSVT

New Member
ericgibbs said:
Using circuit 1, 2, or 3 driven by 7805 Vreg +5V, would mean that the relay would have to a 5Vdc coil,,,, what voltage is the one you have.?

Can you post a specification of the relay and switch shown in the picture you posted.?

... it will remain ON all the time while the power is switched on.

The button is controlling the power going thru the circuit, and outputing at the other end...it's a momentary switch, so as soon as I let go, the output ceases, correct?

Here is the data sheet on the relay...model 700-HJ32Z12

https://www.ab.com/en/epub/catalogs/12768/229240/229266/229643/229705/tab5.html

And more info here...
https://www.ab.com/en/epub/catalogs/12768/229240/229266/229643/229705/tab3.html

If the 555 can take 12v, then I also have 7812's I can use...
 
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