Hi Guys,

This post is in relation to a previous one I posted, however the question I am asking in the title is different hence a new post,I have also learned more about how the circuit works and update the circuit diagram, if this is not allowed please could the mods remove my previous post?

I have an alarm system where the control panel is connected to the contacts of a relay (relay 1 on circuit diagram) on a laser beam module. When the laser beam is broken the relay energises closing or opening the circuit dependant on what pins you are connected to (pins 3, 4 & 5 on circuit diagram) and this is what triggers the alarm. The problem is the relay is re-setting before the alarm control panel can detect the change in state, so I need to keep the relay energised for a second or so longer.

This is the circuit diagram I have created from the PCB, please note that this is not my design, I have simply drawn the diagram with the assistance of my multimeter, I have gone over it several times and believe it should be accurate. The majority of the capacitor values were taken from in circuit readings:


What would be the best way to keep the relay energised for longer?

Is a delay off circuit the way to go?
I found this on google:


As you can see the diagram on the right looks similar to Q7 & R14 in my diagram, could it be simply a case of adding the capacitor and diode to the current circuit? Or even adding the additional resistor and transistor?

A 555 timer was also mentioned previously, would this be better than using the above?

Please also bear in mind I am very limited for space in addition additional components.

Thanks

 

Hi Guys,

This post is in relation to a previous one I posted, however the question I am asking in the title is different hence a new post,I have also learned more about how the circuit works and update the circuit diagram, if this is not allowed please could the mods remove my previous post?

I have an alarm system where the control panel is connected to the contacts of a relay (relay 1 on circuit diagram) on a laser beam module. When the laser beam is broken the relay energises closing or opening the circuit dependant on what pins you are connected to (pins 3, 4 & 5 on circuit diagram) and this is what triggers the alarm. The problem is the relay is re-setting before the alarm control panel can detect the change in state, so I need to keep the relay energised for a second or so longer.

This is the circuit diagram I have created from the PCB, please note that this is not my design, I have simply drawn the diagram with the assistance of my multimeter, I have gone over it several times and believe it should be accurate. The majority of the capacitor values were taken from in circuit readings:
View attachment 127754

What would be the best way to keep the relay energised for longer?

Is a delay off circuit the way to go?
I found this on google:
View attachment 127755

As you can see the diagram on the right looks similar to Q7 & R14 in my diagram, could it be simply a case of adding the capacitor and diode to the current circuit? Or even adding the additional resistor and transistor?

A 555 timer was also mentioned previously, would this be better than using the above?

Please also bear in mind I am very limited for space in addition additional components.

Thanks

A big electrolytic capacitor in parallel with the relay coil can keep it pulled in a second or two longer - but you'd have to make sure the initial charging current doesn't damage the alarm circuitry.

A 555 monostable shouldn't pose any risk to the driving circuit.

 

The second circuit. The one with the relay on the collector side of the transistor.

 

A big electrolytic capacitor in parallel with the relay coil can keep it pulled in a second or two longer - but you'd have to make sure the initial charging current doesn't damage the alarm circuitry.

A 555 monostable shouldn't pose any risk to the driving circuit.

Thanks, I did try that, the biggest i had to hand was 330uf, unfortunately that didn't work, cant really go too big as I am very limited for space.

The second circuit. The one with the relay on the collector side of the transistor.

What would be the best way to implement this into the current circuit? Could I get away with simply adding the capacitor and diode behind R14 and the base of Q7, or should i add an entire new diode, capacitor, resistor and transistor?

Thanks