Designing a Custom Bluetooth Upgrade

[Matthew Jeschke]

The prototype board for bluetooth audio and SD card MP3 player.

The circuit to decode J1850 VPW

 

[clandr1]

This is one of the most impressive projects I’ve seen. I barely understand it, but impressive nonetheless

 

[Matthew Jeschke]

Thanks! It's fun... Has been on my wish list to build along with a handful of other circuits for tuning. This is a good way to get my feet wet though.

My other ideas include a Knock Sensor breakout circuit (could listen to knock on headset, record it, or better calibrate it)

And a narrow to wideband adapter.

18650 battery charger / management (could use as a backup battery). These are SUPER cheap and inside of EVERYTHING but marked up astronomically.

J1850 datalogger (plug it in and it captures PIDs to an SD card). Would be great to troubleshoot intermittent drivetrain issues. I think HP tuners sells something similar but why not make my own.

etc. etc. etc.

I just happened to start with the blue tooth audio stuff.

This forum is the BEST. I've not have been able to build my truck if not for this forum! Excited to share this project. Hopefully I can get it far enough along to cut prototype boards and share them here.

 

[Matthew Jeschke]

Took a while but finally found pinout for head unit. I'm going to start powering this up with my lab bench...

CHEVROLET Car Radio Stereo Audio Wiring Diagram Autoradio connector wire installation schematic schema esquema de conexiones Anschlusskammern konektor

www.tehnomagazin.com

After a bit more research it appears the head may use E&C Data which is a standardized protocol for audio systems / radios???

Radio Data System - Wikipedia

en.wikipedia.org

May have gotten even luckier. I need to rig up my tape deck and rear audio station to the test bench with the radio. It appears there maybe dedicated control lines for the remote devices.

C2 Radio Pin 11 "Gain Control Signal"
C2 Radio Pin 12 "Remote Audio Return (Rear Seat Audio) - maybe I can patch in there to the AUX lines.
C2 Radio Pin 13 "Radio Control Signal (Rear Seat Audio).

I wonder if this is the same control signal / line for the tape deck? I don't see anything in harness titled "tape deck"

I need controls for
Play, stop, pause, next, previous, ff, & rew

Radio C3 Pin 10-12 provide an aux audio in

 

[Matthew Jeschke]

I have the serial "Entertainment & Comfort Serial Data" coming up on my oscope. I also found this which maybe useful. Somebody appears to have decoded the serial control messaging...

TLCDCEmu - Protocol description

tlcdcemu.sourceforge.net

Above link is incorrect for vintage of my truck, 2001 Delco Electronics. This is the correct:

The GM Entertainment and Comfort serial bus

It's referred to as the Entertainment and Comfort Serial Data protocol. Physical layer is as follows:

Single-wire communication
Two voltage states:
High (idle): Near-battery voltage (~12 V), pulled up via ~22 kΩ resistor
Low (active): Pulled to near-ground (0 V), typically using an NPN transistor or 1 kΩ pulldown
Data rate: 1000 bps (1 kbps), asynchronous
Bit encoding (pulse-width modulation):
Logical 0: 111 μs LOW pulse + 889 μs HIGH
Logical 1: 667 μs LOW pulse + 333 μs HIGH
Media access: Carrier Sense Multiple Access (CSMA) — modules wait for ≥15 ms of bus inactivity before transmitting

 

[Matthew Jeschke]

This is interesting... The logic level (voltage) seems to be driven by ignition voltage. I'll have to build a special circuit to reduce that down to 3.3V for a standard microcontroller.

It also doesn't appear to be J1850 VPW but is somewhat similar. It's closer to a RS-232 but the logic level drops between bits. Unfortunately my scope couldn't decode the signal when the logic level drops out between bits like that.

I can create a edge trigger ISR that detects the first edge. Then switches that to a timer ISR that samples in middle of the bit to see if it's a zero or a one and shifts that into a register. Once an entire word is read and parody checked, pushes it out to a byte register that can be read in the main application.

Probably more detail than necessary here but I keep checking back here for my notes. V1850 VPW (Class 2 serial data with P01 / P59 controllers) could utilize the same decoder if I write it correctly.

 

[S33k3r]

Is it driven by the ignition voltage, or is it switched on via the ignition voltage? Is it possible it is on a different circuit and the ignition is just a momentary switch?

 

[Matthew Jeschke]

I should be more clear the voltage level is the same as the ignition level voltage. I believe the circuit is isolated by the radio fuse.

The trick is converting the voltage level down to what a microcontroller takes. Will need to be between 0 and 3.3 V. Shouldn't be to bad though.