I'm about to permanently wire my XEDE map switching wires into a switch and I was wondering if I can wire a LED into the circuit? In other words, would the LED adversely affect the loading of Map Bank 1? If it is possible to include an LED, do I wire it in series, or do I ground the LED separately? I've attached a diagram for clarification...



l8r)

 

Good idea!

I would imagine that the resistance across that LED is probably pretty negligable. Try it!

d

 

Hmm, yeah, but which way? I'm inclined to just wire it in series.

Got my keyswitches today and got the WRC shift light .. so hopefully I will have everything wired in this weekend.

l8r)

 

Oh, I definitely think you should wire it in series.

d

 

Ok, I measured the voltage on the map switch wires and it is 4.50 Volts, which is too much to simply wire an LED in series. So, the next question then is, can I wire an LED in parallel with a resistor and not affect the XEDE's map switching ability? (see pic)



If somebody from Vishnu or someone with an electronics background could please chime in here, I'd be much obliged.

l8r)

 

Or a 2 color LED with a different source so that it can be green for map 1 red for map 2.

 

Don't wire in series - with that kind of voltage drop you will blow the LED and then the switch will have no effect. Adding a resistor would alter the original circuit.

The best thing to do is to wire in parallel, as this won't affect the original circuit. The ideal way would be to use a double-pole switch (DPST) rather than the single-pole one you have (SPST) - one that switches two sets of contacts when you throw it. Wire the XEDE to one set and the LED as a separate circuit to the other (with necessary resistor).

However, your parallel circuit will work OK if the black line is pulled up to 4.5V when the switch is turned on. You will need a 220 ohm resistor for most LEDs at that voltage.

 

Good info.

d

 

Yeah, I thought of using a DPST switch, unfortunately I didn't think of it soon enough, though. I already bought a SPST switch, and I don't feel like buying another one.

So if I wire the LED and resistor in parallel (i.e. with it's own ground), how will that affect the original circuit? Will it drop the voltage of the current on the wire going into the XEDE as well?

l8r)

 

In parallel, the voltage will not drop at all (that's what a series circuit would do). However, it will draw slightly more current, approx 20 milliamps, but that should be negligible to the circuit. It is probably a simple electronic switch in the XEDE that is controlled by shorting the red and black wires, and a few millamps won't affect that.

How did you measure the 4.5V - by connecting your multimeter between the red wire and ground, or between the red and black wires on the XEDE? If you measured it from ground, then you're good. If the red is always at 4.5V, then the black is the one that is switched.

 

I measured it both ways.

Thanks for your help. I really appreciate it. Here's a pic of the work-in-progress.



l8r)

 

Nice work! I guess you don't smoke then!

 

Ludi

Are there two key switches there? What is the second one for?

d

 

It has been a long time but the Xede maps select black wire is ground. The red wire is internally pulled up within the Xede to +5v. I have no idea what the pullup resistance is, but if you source too much current from that line the Xede may have issues. Without explanation make sure that you don't put the red wire in the region around 2.5v for any length of time.

Also note that an LED cares about current across the diode junction. The resistor sets the current as a function of the LED's supply voltage. There are many (google it) led resistor calculators on the web.

A LED in series to ground, if it pulls too much current, might cause the map to switch. You will want to use an LED that requires as little current as possible to achive the necessary brightness. You will want to refer to the LED spec sheet when selecting the LED. Also take into account my note above on input voltage.

 

Just a thought but why not use a relay to open and close the Xede map circuit?