USB ALDL Cable For BumbleBee This is a Nokia CA-42 communication cable. I got it off E-Bay for $2.68 free shipping. It has been modified to be an USB ALDL (Assembly Line Diagnostic Link) cable for communiting with 1989-1995 GM engine computers. These GM engine computers use 5 volt TTL (Trasistor Trasistor Logic) data.
USB ALDL Cable For BumbleBee This is the cable and a level converter I made. Most older cell phones used 3.3 volt TTL and the engine computer uses 5 volt TTL so a converter is needed. The CA-42 cable is based on TTL to USB bridge PL2303. Some versions of this chip are 5 volt tolerant, then no converter would be needed. Not knowing which version of the chip was in the oversized USB plug. I made the converter to be safe.
USB ALDL Cable For BumbleBee The converter will be mounted in BumbleBee and the cable will plug-in with a laptop when needed. The original ALDL connector did not come with the wiring harness so I used a two pin power connector. This will work just fine as the engine computer is transmit only. So the two pins are receive and ground.
USB ALDL Cable For BumbleBee This is the level converter from the front with a dime for scale. It needs a 7/16" hole to be mounted. I will mount it somewhere out of sight. I will most likely put it under the driver side dash like most newer cars.
USB ALDL Cable For BumbleBee I built the level converter circuit DEAD BUG style and potted it with casting resin. This is the same casting resin I made the Allspark with.
USB ALDL Cable For BumbleBee Sorry this shot is a little out of focus but as you can see all the electronics are in there. This converter takes 12 volts DC and regulates to 5.1 volts to match the ECU (engine control unit) and 3.3 volts to match the Nokia CA-42 cable.
USB ALDL Cable For BumbleBee Maybe it's the bubbles in the casting resin that makes it look out of focus. I salvaged some parts from old electronics and some I purchased. Even if I had to buy all the parts it would only cost about 8 dollars. The male and female plugs are the most expensive parts of this level converter.
USB ALDL Cable For BumbleBee I used a low power adjustable regulator LM317LZ. I used this regulator as it has a high noise immunity and does not require capacitors to regulate properly. Since the 12 volt power in cars can be very noisy I used two capacitors. An input bypass capacitor 0.1µf and output capacitor 10µf (small silver can, it's a surface mount).
USB ALDL Cable For BumbleBee I used one surface mount resistor (10K ohm) and one surface mount capacitor (10µf) the remainder of the parts are thru hole components. All resistors are 1/8th watt (i.e. small resistors).
USB ALDL Cable For BumbleBee This is a LM317LZ voltage regulator. The resistors set the output voltage to 5.05 volts but the acutal output is 5.1 volts. The slight difference is due to the 5% tolerance on the resistors. This is close enough to match the ECU.
USB ALDL Cable For BumbleBee This is the 3.3 volt circuit. It is very simple. It's just a zener diode and a resistor. Because the battery voltage in a car can vary, I powered the zener circuit with the regulated 5.1 volts. Both 5.1 and 3.3 voltages are very stable and noise free. Both circuits were tested with unfiltered 12 volts DC applied.
USB ALDL Cable For BumbleBee This circuit shows a bidirectional voltage shifter. This Application Note provides more detail. The technique is unique because it uses a single MOSFET transistor and is bi-directional. I used a BS170 MOSFET because that's what I had laying around. There are better choices but this is what I already had and it works fine. The drawing shows how I am using this, read the application note and research what will work for you. And YES ALL THREE circuits are in that little thing!!!