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Combining HDD LEDs
- Thread starter RWIndiana
- Start date
Chuck(G)
25k Member
If in doubt, use a blocking diode. But I don't see the purpose in this.
A Schottky diode will have a lower voltage drop. Assuming that the cathode side of the LED is ground and it is being driven on the anode side, put the diode in series with the anode/+ side so that it won't allow electricity to backfeed from the other drive when one is on and one is off.
Do you mean you think a diode would be unnecessary?
Chuck(G)
25k Member
No, definitely use a blocking diode. I mean, I don't see the purpose in the whole scheme.
maxtherabbit
Veteran Member
Seems pretty clear he wants to use the single activity LED provided by almost every PC chassis to reflect the activity of multiple different disk systems
Chuck(G)
25k Member
Well, okay, then. I'll add some cautions.
There are, generally speaking, two ways of driving an LED--and they're not compatible. One way is to connect the LED between the active device (i.e. transistor) and the +5 rail with an appropriate current-limiting resistor. The other way is to connect the LED between the active device and the 0 volt rail, with a limiting resistor somewhere in the hookup.
One is not compatible with the other, even with blocking diodes.
There are, generally speaking, two ways of driving an LED--and they're not compatible. One way is to connect the LED between the active device (i.e. transistor) and the +5 rail with an appropriate current-limiting resistor. The other way is to connect the LED between the active device and the 0 volt rail, with a limiting resistor somewhere in the hookup.
One is not compatible with the other, even with blocking diodes.
There are many types of drivers, and Chuck is right, you will want to make sure they are the same, or that you find a solution that deals with whatever each one is together. You might be able to follow the traces on the PCB and find out, or do some testing to find out.
Usually one side or the other will be switched, and you don't know if that switch is a push/pull type of switch that can source or sink current, or whether it is a switch that allows current or disallows current.
Controller 1 anode (usually red)
Controller 1 cathode (usually black)
Controller 2 anode (usually red)
Controller 2 cathode (usually black)
I would begin by trying to see if the cathode of both of the above are directly grounded. Maybe follow the PCB. Measure ohms between it and a ground plane and if they are direct connected, you should be able to use the Schottky diodes on the anode sides. Connect only one cathode side (both are ground).
You could do the same thing with the positive rail. If both the anodes are connected to the 5V rail directly, just connect one of them to the anode side of the LED. Then use the Schottky diodes on the cathode sides to only allow power to go one way.
If it is something different post back!
Usually one side or the other will be switched, and you don't know if that switch is a push/pull type of switch that can source or sink current, or whether it is a switch that allows current or disallows current.
Controller 1 anode (usually red)
Controller 1 cathode (usually black)
Controller 2 anode (usually red)
Controller 2 cathode (usually black)
I would begin by trying to see if the cathode of both of the above are directly grounded. Maybe follow the PCB. Measure ohms between it and a ground plane and if they are direct connected, you should be able to use the Schottky diodes on the anode sides. Connect only one cathode side (both are ground).
You could do the same thing with the positive rail. If both the anodes are connected to the 5V rail directly, just connect one of them to the anode side of the LED. Then use the Schottky diodes on the cathode sides to only allow power to go one way.
If it is something different post back!