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...

Is this clear.?

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Eric
"Good enough is Perfect"

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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.

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....

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

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..

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

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?

 

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

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

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

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

 

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.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

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?

 

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.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
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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...

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Again, I appreciate all the help
Thank you

 

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..

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/