Alec_t, this will isolate the 555.

 

Still wrong
The opto wiring and bulb part.

Do you need a 48V relay

 

Why does your alarm system need such a high voltage supply?
Is this a school/college project?

 

I need a 48 volt relay because of the power supply is 48 volts. This alarm is a plug-in module for the annunciator signalling system of a substation. How do I wire the opto and the bulb? I am already running out of ideas but never give up just yet. I am actually an electrical guy but like to do electronics thing as a hobby. I might do the experiments until I come up to the solution but probably more misses though. I'll appreciate if you guys can lessen my predicaments.

 

I could draw up a circuit if you could explain what you want.
All the details are necessary to draw a complete schematic.
Plus specify the components you can get easily.

 

Why not just drive a relay with the 555 and light the lights through the relay contacts?

 

I'm still unclear as to the intended operation of the circuit.
Which of the following statements is correct?
1) With none of the Alarm, Test and Acknowledge switches closed following a Reset, the 555 and lamps are off.
2) When the Alarm switch closes it self-latches (i.e. is not dependent on the SCR for latching).
3) The 555 won't start pulsing until the Acknowledge switch closes momentarily.
4) The lamps can't switch on until the Acknowledge switch has closed momentarily.
5) Once the 555 starts pulsing it won't stop unless the Reset occurs.
6) Momentary closure of the Lamp Test switch does not cause the lamps to latch on.
7) The lamps do not flash when the Lamp Test switch is held closed for a prolonged peiod.

 

The intended operation is when an alarm is active, it triggers the relay and the lamps should flash. If the acknowledge is press, the lamps should be steady lit. When the alarm is gone or non active, the relay should de energized and the lamps are off. When you press the lamp test the lamps should be on.

 

R!f@@, all the components in the drawing were readily available at hand. That is why I have selected those components. What other information you need I will be happy to supply you. Thank you in advance for the efforts you did all guys out there.

 

So what is the purpose of the SCR? In post #28 you haven't specified any latching action.

 

Specify how the switches are operated.
Like, Does they latch or are they temporary ?
How is an alarm activated ?

 

Does the bulbs need to be 5W types or would LED suffice ?
And can you get DPDT relay or you only have the SPST type ?

 

The SCR was supposed to latch when acknowledge is press. All the switches were momentary non latching except for the alarm and reset. The alarm will be activated by the alarm signal from the voltage source. The alarm signal as a switch is just to show the contacts but it is actually a relay contact driven by an alarm outside of the circuit. The lights would be an LED and the relay can be a DPDT.

 

Answer Yes or No. If NO, Specify why.
1. Lights can be LED's ?
2. Reset is a latching type ?
3. Alarm Signal is a Latching relay contact you have access to ?
4. Lamp test is just to test lights are OK?
5. Ack. is used to test the Alarm ?

 

Answer Yes or No. If NO, Specify why.
1. Lights can be LED's ? Yes
2. Reset is a latching type ? No, Momentary Off but normally closed
3. Alarm Signal is a Latching relay contact you have access to ? Yes
4. Lamp test is just to test lights are OK? Yes
5. Ack. is used to test the Alarm ? No, to stop the flashing of LED and keep it on until the alarm is gone.

 

I guess you don't need an SCR then, since Alarm Input is a latching type.
Why do you think you want an SCR ?

 

So, the SCR needs to latch the Ack signal and over-ride the 555 to hold the LEDs on. But should the LEDs go off when the Alarm signal goes, or only when the Reset occurs?

 

Yes, you are right Alec_t, the SCR need only to latch the Ack signal and over-ride the 555 to hold the LEDs on. The LEDs goes off when the alarm signal goes off. If we can latch the lamps from the 555 after pressing the Ack, then we don't need the SCR.

 

If I've understood you, I think this circuit willl do what you want. I haven't shown the relay. I've used a PNP-NPN pair as a latch, rather than an SCR (which requires more holding current).

 

Yes Alec_t, that's more likely what I need as shown on the simulation. The relay might be located somewhere in parallel with the LEDs but might need a driver though. I'll do it in the PCB and update you on the progress. Thank you very much for your help.