pcmhacking.net

Hi all,

Gampy,
The effective resistance from adding the Sparkfun board in parallel with the AllPro is approximately 9.5k Ohms.
So, suffice it to say that adding a resistor to the board will NOT make it work. (If the AllPro had the HIGHER resistance and the Sparkfun the lower than I'd say go for it).
Seems to be that the Sparkfun may be sending tester present messages that the AllPro isn't?
Mike

The hardware used in the allpro (I forgotten the technical name of it), holds the bus close to ground and can prevent communication between between devices.

Other tools may be providing passive power to the bus which is whats allowing communication.

Hi all,

Tazzi that makes sense to me - the allpro literally has a 10k resistor from the data pin to ground.
I assume the sparkfun has a 240k resistor, which allows the pin to "float" compared to the allpro.
It MAY be worth replacing the resistor in the allpro with a larger value and see if that fixes it.

Mike

I think there's got to be a way to fix it from the outside though. It's always been reliable for me when I have the LX on the other side of my Y adapter, and it's always been reliable in my car. So I don't think we need to modify the AllPro to make it reliable in a bench harness. It just needs something else on the bus that does whatever the LX is doing.

I'm curious if a schottky or other fast switching diode protecting the rx/tx for proper communication would help. I don't have any of the mentioned devices to test.

Welp, as soon as I get some kind of confirmation that R13 is in fact the 10k resistor pulling down the bus, I plan on getting it swapped for a larger one. (to small for me to do, I shake too much)

I also need to find out it's Package (foot print) ... It's small is all I know and I can't read the number so well, it looks like 1002 through my chincy magnifier.
Do I need to use a surface mount or can I cobble on a typical barrel type carbon film. I don't think I have an appropriate surface mount in stock.

Requiring a second tool (or device/module) on the bus is unacceptable IMO.

As far as I'm concerned it's broken as is to me ...

A further analysis of the internal parts on the board is realistically needed. I wouldnt go changing resistors and parts without fully understanding the circuit as it may be critical do how a component runs (transistors, opamps, regulators ect).

Does this schematic help any?

I think its more likely extra capacitance on the bus effects the waveform. I cant see it being resistance as it should work with any number of other devices 1 to more than 5 and I just cant see it being a level issue a 'y' cable can fix. But that 'y' would add capacitance to the bus. Im definately no analog signal guru though.

An interesting thing I've found is it acts like it gets hot ...
If it's left unplugged for a while, then plugged in and used immediately, it works perfect sometimes, that is the only time I can get it to work, but after some minutes it's all done until it sets for a while again.

With this latest change to VehicleSetVPW4x(...) it is MUCH better, though still not reliable enough to attempt a write safely IMO.

I see it this way ... It is currently junk to me, what do I have to lose, it can always be put back unless it gets taught to smoke.