LED light help needed (booster? converter? relay?)

Dave001 said:

So I have a nurse call system that I need to modify. Currently, when a room call is activated the control panel sounds an audible alarm and illuminates a small 2 volt LED. Each patients room has a call button in both the room and bathroom, and it illuminates a different LED on the control panel for room or bathroom. I want to use the power off the 2V LED as a signal/ trigger to illuminate a LED number to the corresponding room (simple 3D printed plastic backlit number). The purpose for this so that you could see from a distance what room has called and not have to walk right up to the control panel.

I have come up with 2 variations for how I could wire this and need some help to go further. The sketch helps to explain alot.

- Each variation needs to use a buck converter? booster? or relay? to go from the 2V input signal to power the LED number which will be 3-6V.

- Are there other options on a control module?



Variation #1

The signal input wires would join to the same terminals on whatever controller I am using. If the room call 2V LED is activated it would also send power back to the bathroom LED, which will send unwanted power back into the control panel and may cause damage. So the signal input wires would need diodes(?) On every wire? Or just the positive wire?

With this setup I would only need to use 1 control module per room, but have to install diodes.



Variation #2

The output wires would terminate on the number LED. If the room call is activated it would also send power back to the bathroom controller. I would also have to install diodes here, or Depending on what controller I am using it may not be needed. For example a 2 pole mini relay? If that exists?

With this setup I would need to use 2 control modules per room, and not need diodes with a relay?

I need to do this for 8 rooms so the amount of work is something that I am keeping in mind.

The large LED room number (#4 in pic below) is not a display of any kind. Its a plastic 3D printed piece with LED's inside of it that light it up download facebook video.
I will be using an external power supply for these LED numbers, not getting power from the panel itself.

Thanks in advance!!

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Les Jones said:

If you connect pins 1 & 2 directly to the LEDs The original LEDs will not iluminate as the forward voltage of the infra red LEDs in the solid state will only be about 1.3 volts so it will clamp the voltage down to this level. From the data sheet these devices will switch on with 2 mA forward current. As the worst case forward voltage drop is 1.5 volts you will need a series resistor of about 0.5/0.002 = 250 ohms. The next lowest value in E12 series resistors is 220 ohms. This will make the original LEDs slightly dimmer. It would be very helpful if you would trace out the drive circuit to the LEDs so we can give you better advice rather than us just guessing.
These solid state relays are quite expensive .(About £2.00 + VAT each. ) I think crutschow's suggestion in post #14 is better as the opto isolators are cheaper.
One other point. how many rooms does the system cater for. ? If it is a large number the LEDs may be multiplexed so a different approach would be required.

Les.

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Les Jones said:

If you plan to remove the original LED first do the following tests.
Measure the current through the original LED.
Measure the voltage between the wires that connect to the LED with the LED disconnected and the pannel in the condition where that LED would be iluminated.
When you connect the VO14642 make sure that you have the polarity correct. As the LED driver circuit is probably a constant current source if it is connected to the VO14642 with the wrong polarity it will probably destroy the IR LED in the VO14642 by exceeding it's reverse voltage rating.

Les.

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Vons Garage said:

Remember that a nurse call system can be used in a life and death assistance call to staff. In the US it is subject to NFPA and UL criteria. Please be careful.

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