pcmhacking.net

Hi all;

Gampy, changing that resistor BY ITSELF may well cause it to not work at all.
IF you wanted to try modifying the circuit, you would want to try changing ALL of the 10k resistor - R10 - R13 - to the same value (try 100k) so you don't change the ratio of the voltage on the two pins of the comparator.
However, I suspect that Antus is correct about the added capacitance from the Y-cable.

Mike.

Obviously I'm getting pressured not to try replacing the resistor ... So, I'll take the advice!
Y'all are far smarter then I with this shit.

So, I cobbled (alligator jumpers) the SparkFun onto the bus along side the AllPro.
It most definitely helps!

I was able to,

Select Device: AllPro
. Verify
. Read (9:44)
. Test
. Calibration (1:42)
. Clone (9:18)

Select Device: SparkFun
. Verify

Select Device: AllPro
. Verify
. Read
. Clone

Select Device: SparkFun
. Verify

Select Device: AllPro
. Verify
. Read

Without a single hickup on either device!

Without ever closing PcmHammer (v014 basically) ...

An hour later, still connected, no reboots and it still works!

The AllPro has NEVER worked that reliably for me!

Yes, I am happily impressed.

However, I do not believe that to be a viable solution ...

If it's added capacitance wouldn't that just involve adding a capacitor instead ??

I think so. I'm not sure what size cap to start with though.

Yeah. Also dont know if it needs to be inline or off to ground. I think off to ground would filter the signal, so perhaps its inline. I know in the very first incarnation of my test bench I used stranded wire for the bus, over a short run across the bench. Then because it was loose I tried a couple of knots in the wire just to hold the strands together. The electrical properties of the knots changed the signal timing enough to make the data connection very unreliable, and some devices wouldnt work at all. It took me a while to figure out what was going on but eventually I took the knots out the cable and it fixed everything. The analog world has strange properties.

I figure the added cap probably needs to be in parallel, since attaching a Scantool LX in parallel is all it takes to make the AllPro reliable.

Anyone have a meter that measures capacitance? I wonder what it would read if hooked up to the VPW and ground pins on an LX.

Ive got an LCR-T4 but I think the capacitance will be so low it wont determine its looking at a capacitor. https://www.youtube.com/watch?v=YyUkpBXc8cQ

Hi all;

The Y-Cable will add a small amount of capacitance - in the PicoFarad (pF) range: most likely on the order of 10 to 20 pF.
And yes, it will be parallel capacitance added across the data line.
Not sure how much will be added from the OBDLink device.

Mike

p.s. I THINK this is the range it can measure:
https://www.amazon.com/Aideepen-Mega328 ... UXHYY?th=1
"Can measure capacitance of 30pF-100mF , resolution 1pF"

MudDuck514 wrote:And yes, it will be parallel capacitance added across the data line.

Translate to dummy please ??
Caps have +- right ??

Not all types do. Ones as small as in the pF are generaly tantalum type and are not polarity sensitive. Search 20pf capacitor on any of the online stores and you should get results. Or once you know what your looking for, the small, circular, flat type, you can probably fine on an old PCB. It should say 20 on it, and it'll be one of the smallest ones on there.

I have some of these: Ceramic Disc Capacitors 1Kvolts 22pF 5% .25LS NPO.
Believe I have some more of different values, will have to dig.