As you all know I purchased a laser interceptor to protect my bike from lidar speed measurements.
The design of the LI allows you to hear the alerts spoken in voice. The LI was designed for a car in mind but I wanted to adapt it to a motorcycle.
I also have an Autocom unit. Unfortunately, due to the way the LI was built. You can't interface the two directly. Connecting the LI to an autocom directly will fry the LI CPU's preamp circuit. Autocom is designed for single ended inputs. The LI is designed with a differential output. I originally fried my LI preamp trying to bring these two devices together. I eventually went with a LED notification but lost the ability to hear the names of the gun.
I set out on a quest to bring these two devices together and found a solution to this problem. So I bring to you my first publicized LI mod.
Hooking up a LI to your Autocom. *I posted this on the LI forums so it's a copy/paste job. Bear with me*
This mod kills 3 birds with one stone.
1. Allows you to hook up your LI to your autocom.
2. Provides ground isolation so if the 3.5MM plug is disconnected and touches ground. No damage will occur.
3. Removes engine whine and noise that was associated with my first version of this mod (this is v2).
Fully tested, works perfectly!
The transformer is rated at 300hz-5khz. It's meant for telecom applications where quality in the vocal range is required. It's not a HI-FI solution but works perfectly for the LI's voice skinning feature.
Ok!, I figured it out! My problem was I was interfacing a differential speaker to a single ended input (my aux input)
In my brainstorming I thought that a GLI would solve my problem. Unfortunately I was unsure how to hook up a differential output to a GLI since you can't ground the wire.
Well turns out, a GLI approach is exactly how you convert BTL audio to single ended..
Now I will teach you how I wired my LI to the CPU. I will explain at the end of the tutorial how you can do it without soldering or voiding your CPU. To do so you will mount the transformer externally. I chose to do a internal install because it's safer, Remember, A speaker wire to ground is death to the preamp. This is why I don't want anything mounted externally that shouldn't be.
What you need is the following.
LI CPU (Of course)
Small Philips Screw Driver (only needed to place the transformer inside the CPU, If you wish to mount it externally you can do that as well)
1 Radioshack 6FT Stereo cable extension. Item#42-2387
1 Radioshack Isolation 1:1 transformer. Item#273-1374
A voltmeter/continuity tester *optional
Open up the LI cpu case,
Remove the isolation transformer from the packaging. Set aside for now.
Remove stereo cable from packaging.
Now take your stereo cable and cut the cord with scissors. (halfway, far end, it doesn't matter. You only need one side (so close to one end is better)
There are three wires inside. Two are colored, one will be silver stranded uninsulated. Take the two wires with insulation and strip a quarter inch. Next twist these two together (this will turn the li mono output into a stereo output).
Get out your transformer and unwind the wires, there should be 4. Black/White/Red/Yellow
Ok find the 8 pin junction block on the li.
Place your LI on a desk. You should see this....
Back of unit facing you (as if you were looking at the pins directly)
White goes to pin 1 Differential Positive
Black goes to pin 5 Differential Negative
Yellow goes to the two wires you twisted together (there should be three together now)
Red goes to the silver uninsulated wire (ground)
I put in side adhesive tape to support the transformer to prevent it from banging around. It's a 3M automotive tape. The same stuff I use to secure my heads to my bike (the stuff is magic it won't go no where once you put it back together)
Make sure you don't block the screw holes for when you reassemble the unit. Also very important, put electrical tape on your exposed contacts so they don't short out. Electrical tape around the transformer as well (I added this after I took the pics just to be safe).
Use needle nose pliers to make a conduit to route the audio cable out of. Reassemble CPU, plug in the device and you're all set.
You can remove and connect the LI cpu to the aux unit as you wish. Powered or unpowered as there is no physical ground connection to the speaker wires.
Ok I got a few comments about warranty issues etc. You can very well void the warranty doing an internal install (the points that the wires connect to are big, there are no surface mount connectors nearby to which you can damage so an internal install is safer IMO due to sensitivity of the speaker wires being unable to ground. I've blown a preamp before from grounding a blue speaker wire (external install) and I voided my warranty to fix it since I knew that it was my fault. Cost to fix was about 7$ but I still bought a second cpu anyway. I use my fixed cpu to do my testing, then I implement it on the newer 7.06 cpu I have on my bike once it's finished. (I don't trust using my previously damaged cpu in real world conditions).
If you wish to do an external install here's how.
Prepare the stereo cable as described in the internal install. When you wire the insolator. Just use the blue speaker wires coming out of the back of the unit. That's it. I can't give any more information as I don't recommend an external install. The isolators wires are very small so make sure you mount the transformer to something sturdy so it doesn't rattle around. Place tape on the stress points of the cable (solder joints etc) so they don't break under vibrations.
Here's a picture of my setup.