Uber-easy DIY USB ALDL Cable

[GaryDoug]

Sorry, I'm only an EE with 45 years experience with this kind of stuff. Won't bother you again.

[RobertISaar]

i never said you were wrong, just that i have my preferences.

[EagleMark]

Sorry, I'm only an EE with 45 years experience with this kind of stuff. Won't bother you again.

You have to understand we discuss and bounce ideas and use everyone's expertise. One thing we never do is offend anyone. So you took this wrong.

We also don't allow bad attitudes. So lose it or just don't come back.

[Six_Shooter]

I just tested this adapter:

https://www.sparkfun.com/products/718

It's part of my Project Lab III kit (school), so I figured I'd give it a try in Tuner Pro.

At first I forgot about shorting the TX and RX pins, but after using an alligator clip positioned carefully, it passed the test.

I then connected it to an ECM on my test bench ('7730 running a stock ARUT MEMCAL $A1), connected as quickly as my Moates cable.

Just thought I'd pass it along.

[FSJ Guy]

I tried a similar one and it worked while the truck was key on, engine off. Once I turned it on, it would only stay connected for about 2-4 seconds and then it lost connection. I don't remember which voltage version I used.

What voltage are you running yours at?
https://www.sparkfun.com/products/718

[Six_Shooter]

Currently I have left it at the as shipped 3.3V setting.

I'm going to make a better test rig that I can plug into a vehicle to do more testing. I need to make sure that it works for my school project though, since I need it to program my Dragonfly board...

[RobertISaar]

this may sound odd, but i don't bother connecting VCCIO to either the 5V or 3.3V settings..... seems to be unnnecessary for these applications.

[89S10_Project]

I just tested this adapter:

https://www.sparkfun.com/products/718
...
At first I forgot about shorting the TX and RX pins, but after using an alligator clip positioned carefully, it passed the test.

Six Shooter, I owe you beer!

I've already got an order laid in for a better cable, but when I read the above, a lightbulb went off.
Got my test harness (two wires to go into the ALDL, one which bridges RX and TX on the Arduino FT232 board) and plugged it in (not into the ECM) while I tested the unit in Tunerpro 4 and 5...

Cable is now "Found and Functional". R&R of the harness reproduces and resolves the problem. Apparently the cable test tests the onboard components all the way to the far side pin header and wants to see loopback on the pin header.

I'm going back out to my truck to see if some combo of futzing with things will get me talking to the ECM. Hope to have good news soon.

[89S10_Project]

I was just able to successfully pull data from the truck whilst it was running!

I'm ashamed to admit that it took me all of a week to get this to happen. At the same time I'm proud to admit that it took me all of a week to get this to happen.

Apparently the TXD and RXD pins must be bridged for successful test of the unit, without it being plugged into the vehicle(as has been said, plugging the unit into the vehicle will not be a successful test).

I did so, tried the FT232 unit. Worked fine. I have another unit, an FT232RL, here- tried it too, it too passed once I bridged RX to TX. This more or less proves the test process wants loopback on the chip TXD/RXD circuit. (Kinda like testing a T1 smartjack, or a POTS jack ;) )

Went to the truck, connected the FT232 unit to the harness in the vehicle. No joy. I couldn't get data with the TX and RX bridged to the ALDL "E" pin (89 S10 Blazer 7747 BTW). Tried in WinALDL and was able to get partial, though useless, data- I couldn't even get TPS volt or anything else useful. Don't care, I'm moving toward Tunerpro and ALDLdroid for my solutions.

Tried the "RXD and TXD bridged with a diode and a 1Kohm resistor) trick. No joy.

Resigned myself to spending $100+ to get a cable and a BT module overnighted (which while a good deal for it, really need to be buying tires)
On a lark, but the FT232 in.. using the resistor and diode network, no joy. Just for S&Gs, I tried the "hardwire bridged TX and RX". Looked good, I clicked "connect"..... and got an endless "connecting" indication, but never a rejection.....

OK, interesting.... I recall hearing something about signal reflection and the TX not being needed on the 160-baud ECMs anyway... so I disconnected the TX side of the bridge.... and the damned thing CONNECTED!

BS, says I... something is fooling me. I pulled up the dash, and darn if I wasn't getting full range data.

I'm also seeing something REALLY odd. My injectors are registering 170% duty cycle. I'll move that part to another thread.....