SparkFun Forums

[druegan]

Hello, I was looking at the variety of wireless transmission boards you have available and was wondering what would be best to basically replace an LED connection drive a wireless transmitter then have the receiver blink an LED every time the source would blink.

So my question is what pin/wiring would I use on what board of yours to make this work best? I was looking at the nRF2401A and the RFM12B-S2 as the most likely candidates figuring I'd somehow use the DATA pins? I'd like to do this as cheaply (but still well) as possible, hence leaning toward the RFM12B-S2. It only has to work within 10ft through walls... Any help would be appreciated.

Thanks in advance!

[stevech]

You can use a pair (or more) of XBee series 1 modules. No additional microprocessor or coding needed.
These have built-in fimware to do "virtual wire" between units.
You study a the XBee documents a bit, (we'll help) and you can setup module A and B as...
A has one of several digital inputs connected to something - say, a push button.
B has one of several digital outputs configured to "follow" the same pin on module A.
So when the pin changes on module A, then it will change as well on B, as an output. You can connect that to an LED or to a relay that controls a well pump, or whatever.

There can be several virtual wire pins.
There can be a module C and D and so on.

You can have virtual ANALOG wires - where the analog voltage coming in to a pin you configure on, say, module B, is replicated on a pin of Module A. The module A signal isn't analog per se, but is a pulse whose width varies per the analog voltage at the other module. Take the pulse width signal and run in through a resistor/capacitor (R/C) integrator and out comes analog.

There are other things you can do with these modules without having to have a connected microprocessor, or do so only at the "base station" end.

if you really want to get fancy with wireless, look at RadioHead: http://www.airspayce.com/mikem/arduino/RadioHead/

I suggest avoiding the $2 radios (ASK or OOK). Too much work put on you to devise modulation and error correction methods.

[jremington]

These would work for short range, at a fraction of the cost of an xbee: https://www.adafruit.com/product/1095

[druegan]

Thanks for the advice stevech and jremington! It's been over a decade since I've done any microelectronics and was looking at this little project to get back into it and learn more about logic (as well as just "getting it done" ). It sounds like for the project itself, jremington's suggestion will work best for me, and in the long run I'd have a lot of fun with the xbee stuff

So here is the project in more detail, and the main problem I've ran into trying to make a "basic button remotely light an LED".

I have an Escort 8500ciPlus Radar Detector I installed on my motorcycle. It had on it's main controller unit (CPU, basically) a connection for a dual LED package, 3 pole connection. I've metered it out and the center is the common, the left and right when there is +2 VDC on one, the other pole has +1 VDC. The colors are Green and Red, I could care less about the Green, that's basically just "Power ON" and is only lit when the Red LED is not. The Red one, the +2 signal on the Left pole, is the "Alert" LED. That flashes.. pretty quickly and is what I want to make wirelessly flash an LED in my helmet. So the distance will be within 10 feet easily, the distance from the rear seat and my head. Going through the seat, probably the fleshy bit (me) and the helmet to get to the receiver mounted in the helmet.

As I've looked into this, even before posting here, the main problem I've come across is that dang +1 VDC to +2VDC rapid change that lights the original/factory LED. It's not as simple as "ON" or "OFF" like any switch I've worked with in the past, or any circuit I simply just switched on or off from the input power.

So the "Data Transmission" is as easy as "a blinking light" but I'm not certain how to wire up the transmitter properly to plug in to there the LED normally would and drive the wireless transmission to a remote LED on a receiver. One person I talked to mentioned having to use a Schmidt trigger.. Which I learned about a long while ago but have no real experience with (or usable memory of ).

So.. any idea how I would "convert" say, that keyfob remote button to a usable transmitter to plug in to this "LED Connection" ? Ideally I'd have the transmitter run off that 2 VDC, but I can always have it run off of the 12 VDC power on the bike. I really need the receiver to be the smallest, lightest part. Not the Transmitter.

[jremington]

An NPN transistor could be configured to switch the pushbutton input on the keyfob transmitter and configured so that it would switch at any desired voltage level.

However, you need to provide more details about the wiring and the voltage levels you are seeing. I don't completely understand what you have written. Can you produce a schematic (circuit diagram)? A photo of a hand drawn diagram would be fine.

[druegan]

2015-02-10 09.18.34.jpg

So here's a basic sketch of what I was talking about. I only metered the voltage on the 3 pins labeled "red" "common" and "green", didn't measure the current or the resistance.

Does that help? It's just an LED on a wire with a telephone headset connector on one end that plugs into the main control box.

Thanks again for all the help!

[jremington]

If you are willing to sacrifice one or both of the LEDs, either could be replaced by the input to an optocoupler, which is also an LED.

The output of the optocoupler could then be used to "push" a switch (make a connection) on a keyfob transmitter.

[druegan]

Oh, I fully meant to replace the LED connection with the wireless transmitter, so how do I wire up this.. optocoupler? to the switch on the keyfob? do I just wire the led connection to it than replace the switch with a connection from it? I've never used (or seen) an optocoupler before .. :$

Thanks, yet again! for the help This is exactly what I was hoping for, something quick and not requiring me to go back for my full EE degree (from an AAS in Electronics )

[jremington]

Google "optocoupler circuit design" or similar for thousands of helpful web pages.

[druegan]

Just did the google. Wow, that thing is cool, and you're right, it's EXACTLY what I need Thank you ever so much jremington!

Now I just need to find someplace to buy an optocoupler (Hopefully the nearby electronics shop) and I'll be all set! (I already ordered the parts yesterday from adafruit you linked me earlier )