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How to control 2 LEDs with 2 cond circuit

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hiker

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To simply state the current setup, I have a remotely located red LED fed by a 2 cond wire from a locally located switch with power. I want to add a 2nd LED (green) alongside the red LED and have the ability to simultaneously turn one off and the other on. So they both would never be on at the same time. And it is not practical to run another wire.

So is there a simple way to control the on/off state of the LEDs by supplying different voltages? I could switch the voltage locally to a range from 5v to 12v and adjust the current limiting resistor. I'm thinking zener diodes located at the LEDs might be a way but I am not sure of the type or circuit design.
 
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To simply state the current setup, I have a remotely located red LED fed by a 2 cond wire from a locally located switch with power. I want to add a 2nd LED (green) alongside the red LED and have the ability to simultaneously turn one off and the other on. So they both would never be on at the same time. And it is not practical to run another wire.

So is there a simple way to control the on/off state of the LEDs by supplying different voltages? I could switch the voltage to a range from 5v to 12v and adjust the current limiting resistor. I'm thinking zener diodes might be a way but I am not sure of the type or circuit design.

Hi,
You could use a bi-colour LED Red/Green and change the polarity of the voltage to the wire pair.
A resistor is required in series with the LED, as usual.

If you used the 5V supply you could a connect a Green LED in reverse parallel to the Red LED.
Reverse the wire supply as in the first example.

Do you follow OK.?:)
 
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Hi,
You could use a bi-colour LED Red/Green and change the polarity of the voltage to the wire pair.
A resistor is required in series with the LED, as usual.

If you used the 5V supply you could a connect a Green LED in reverse parallel to the Red LED.
Reverse the wire supply as in the first example.

Do you follow OK.?:)
No, thanks I don't think that will work in my situation since I'm not really adding a LED. I was trying to keep it simple but...
I didn't want to make this more complicated but I guess I'll have to explain the actual components. There's not a simple LED with rather a 7 segment LED bi-color display. The display has 2 common anodes, one for green and the other for red and one common set of cathodes. Again there is no practical way to add another wire. I want to switch the display from red to green and vice verse. I can add components to either location but can't change the display. The LEDs change from red to green by switching the supplying voltage to one of the two anodes.

So is there a way to do this by maybe changing voltage or polarity. I think zener diodes might work but haven't yet experimented. I don't think changing polarity is a soution since the 7 seg display uses the same set of cathodes for both red and green LEDs. Not sure if the LEDs in each segment are actually separate and positioned maybe on top of each other or composed of a special substance that can turn red and green. As a curiosity, I can supply voltage between 5-12v to both anodes at the same time with a 330 ohm resistor to the red anode and get a color displayed which looks like a pale orange.
 
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No, thanks I don't think that will work in my situation since I'm not really adding a LED. I was trying to keep it simple but...
I didn't want to make this more complicated but I guess I'll have to explain the actual components. There's not a simple LED with rather a 7 segment LED bi-color display. The display has 2 common anodes, one for green and the other for red and one common set of cathodes. Again there is no practical way to add another wire. I want to switch the display from red to green and vice verse. I can add components to either location but can't change the display. The LEDs change from red to green by switching the supplying voltage to one of the two anodes.

So is there a way to do this by maybe changing voltage or polarity. I think zener diodes might work but haven't yet experimented. I don't think changing polarity is a soution since the 7 seg display uses the same set of cathodes.
hi hiker,
This description is totally different from your first description.:)

If you have only two wires how do you control the individual segments.?

Can you post a sketch of what you already have connected, there may be an easy way to do what you want.
 
hi hiker,
This description is totally different from your first description.:)

If you have only two wires how do you control the individual segments.?

Can you post a sketch of what you already have connected, there may be an easy way to do what you want.
Sorry, I don't have just 2 wires. There are 8 wires going from one location to the other. The switching is done at the opposite location from the LED display. I should have run 9 cond wire and instead used only 8 cond. Seven of the conds are connected to the cathodes and switched individually (8 switches total). There are 8 of these displays located at different locations and a total of 64 switches. But each display has an identical separate circuit of 7 cathodes and 2 anodes. Originally I setup the display for only a single color so 8 conds was all I needed but now I want the ability to change from red to green and vice verse. I thought I could change colors (for future capability) like a regular bi-color LED by reversing polarity but it doesn't work that way. Poor planning on my part. :(
I'll see if I can attach the datasheet...

Oh, and there are 7 current limiting resistors, one in series with each cathode line, 470 ohm each, and a 5vdc supply. I used cat5 cable.

Any help you can give will be greatly appreciated.
 

Attachments

  • Stanley 7segment display nb105_107_e.pdf
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hi hiker,
Have downloaded your pdf, give me a while to go thru it.:)
 
OK, thanks.

hi hiker,

Does this pdf represent what you have the moment.?

Just to make sure I am on the same wavelength.:)
 

Attachments

  • hiker1.pdf
    13.1 KB · Views: 128
Yes, that looks correct as I understand the display chip. But actually I don't know the internal circuit. Each segment LED looks to be one component verses 2 LEDs superimposed. When I experiment with different voltage and resistors on the anode side, both anodes on same power, I can get colors green to orange to red. For example, with a 220 ohm resistor in series with the red anode, none on the green anode, 5v shows mostly red color, 12v goes mostly green. But the green (12v) looks bright (almost too bright) and red (5v) looks too dim. My thought was to add one or two zener diodes of the right value in to the mix to cut off most of the current to the anode of which color is not wanted.
 
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Yes, that looks correct as I understand the display chip. But actually I don't know the internal circuit. Each segment LED looks to be one component verses 2 LEDs superimposed. When I experiment with different voltage and resistors on the anode side, both anodes on same power, I can get colors green to orange to red. For example, with a 220 ohm resistor in series with the red anode, none on the green anode, 5v shows mostly red color, 12v goes mostly green. But the green (12v) looks bright (almost too bright) and red (5v) looks too dim. My thought was to add one or two zener diodes of the right value in to the mix to cut off most of the current to the anode of which color is not wanted.

hi,
OK, I'll have look see what I can come with.:)

Now that we have a drawing, others may have ideas.
 
Hi Hiker,

Check this out:

https://www.intersil.com/cda/deviceinfo/0,1477,ICL7665S,0.html

You can use a ICL7665S to switch between to different
voltege levels: +5volt for the red anode(s) and +6volt
for the green anode(s). There are in fact two level
detectors and both are set to 5,5 volt which means
that around +5,5 volt both may be on or off but that's
no real problem because you switch from +5 to +6 volt.
There's no need to calculate a hysteresys because it
will only complicate the circuit and it's not really
necessary.
The highest voltage output will be connected to the
green anode(s) because the voltage drop across the leds
of the green display will also be higher. If this is not
enough to get the same brightness with the same cathode
resistors you can increase the voltage difference even
further. e.g. +5 volt and +7 volt. You only have to
recalculate the trip point for +6 volt.
The fets are old devils and you can use almost every old
mosfet you can get on condition that the maximum drain
current will not exceed 500 mA at +5 volt supply voltage.

on1aag.
 

Attachments

  • Bi-color display.GIF
    Bi-color display.GIF
    9.6 KB · Views: 112
hi on1aag,

If I have followed hikers description correctly.?
There is no 0V return from the displays,
just the 7 lines from the cathodes of the segment LED's going to the manual switches [back at the psu], then to 0V.

Perhaps hiker will confirm this.?


Hope you are well.:)
 
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hi on1aag,

If I have followed hikers description correctly.?
There is no 0V return from the displays,
just the 7 lines from the cathodes of the segment LED's going to the manual switches [back at the psu], then to 0V.

Perhaps hiker will confirm this.?


Hope you are well.:)
Eric you have it right. The 7 cathodes are connect to the cat5 wires which, on the other end, are connected to the 470 ohm resistors at the other location and then to ground.

I suppose I could move one of the 470 ohm current limiting resistors to the display location and connect that wire at the other location to ground. That would give me 0v at the display location.
 
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hi hiker abd on1aag,

on1agg,, Modified you circuit to give a virtual ground for the ic, what do you think.?

Only two LED's shown for clarity
 

Attachments

  • Bi-color display.GIF
    Bi-color display.GIF
    11.5 KB · Views: 111
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Hi Eric,

It's a possibility, but I'm not convinced that it will work
equally well unless you select the two supply voltages
further apart.

on1aag.
 
on1aag or eric,
Thanks. I just wanted to confirm the resistor values as these old eyes are having a hard time reading the diagram:
upper left 47K
lower left 15K (not sure about this one)
The other 2 are 47K I think but diagram looks to have 4K7 ?

Also what voltage appears at the red and green anodes, 5 or 6 v ?

And could I use 4.5v and 6v instead of 5v and 6v ?

Looked at datasheet for irf9530 and not sure which of the 3 leads correspond to the diagram ? They are labeled S G and D.
 
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Hi Hiker,

The resistance values need not be recalculated for 4,5 and 6 volt.

47k, 15k, 4k7 and 4k7.

The highest voltage goes to the green anode(s).

Both sources of the fets are connected to the supply voltage,
the gates are connected to the outputs of the ICL7665S and
the drains go each to a anode of the display.

on1aag.
 
hi hiker,
Taking a step back, can you say who sets the segment switches for the LED's 7 segments.?
Do they have a printed list of segments versus numeric displayed value.?

I would have used 4 BCD lines with a BCD switch which controlled a CA, BCD to 7 seg driver, located at each LED.
Thus would leave 3 spare wires for the colour select.

Is it too late to consider that option.:)
 
hi hiker,
Taking a step back, can you say who sets the segment switches for the LED's 7 segments.?
Do they have a printed list of segments versus numeric displayed value.?

I would have used 4 BCD lines with a BCD switch which controlled a CA, BCD to 7 seg driver, located at each LED.
Thus would leave 3 spare wires for the colour select.

Is it too late to consider that option.:)
The segment cathodes are controlled by a set of relays (one/segment) that are energized by a USB-RS232 interface to TCL program on WinXP. This was a familiar technique that I chose to make the displays computer controlled, from the source of the info that makes the displays useful. So I'm not sure if your idea would work, but if you think it might, please share a schematic.

I'm going to order one set of the components for the method on1aag suggested so I can bench test first. I'm limited on the physical space in the enclosure for additional components so I might, in the end, have to change the cable or run another supplemental line.
 
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