The chip isn't my concern, I'm just tired of finding ecm's in junkyards missing the memcals. Where do they all go? I never see them on ebay, just the ecms WITHOUT MEMCAL!!! Drives me nutz, anybody have any info on making the knock circuit? What about using an older c3 external? Isn't the knock filter just a simple high and low pass filter?

 

Yeah, I've got some good info on this. I found through some digging a chip from Texas Instruments that I guess must be used on newer cars. its pretty much a complete knock sensor chip, complete with filters, intergration time constant, and gain. Its pretty small, you could probably put it and a PIC on a small board that fits in the memcal housing, and you could in theory make a completely tunable knock detector. Its got a serial (SPI) interface, so you'd need a pic to program it. I've been kicking it around, I just haven't gotten around to prototyping it.

the part is the TPIC8101, search on TI's site.

then, you could put some tiny resistors on the bottom side of the board, and make it a total replacement memcal.

you're right, the whole reason I starting looking into it is becuase it sucks to have to go out and buy the new memcals, just for the knock sensor and r-pack.

 

On the '730/'749 ECMs there is a separate input for 'knock'. So yep, an external filter may be used. The knock filter is a little more sophisticated then just a bandpass filter.

The only other part would be the limp home resistors. The cylinder select pin can easily be tied to the proper voltage. It's those other resistors if limp is required.

Then again I've seen pic's posted here of aftermarket MEMCALs and they sure as heck look like they have standard off the shelf (cts) resistor networks on them. One would have to purchase a whole lot of them if they were custom. More then I would think an aftermarket company would. . .

RBob.

 

Doc's hoarding them.
He's got this crazy notion of emulating DeBeer's, but with memcals, instead of diamonds.

Hope, your glad you asked.......

 

That's what I thought, that the limp home stuff was still just a resistor pack. That's good because those are easily made, but what about the knock filter. The 7749 can use the external, that's good news. I guess I have to look closer at the schimatics to see where to run the pins.
The aftermarket company's have generic resistor packs? Do they work in limp home mode?
I know that isn't REALLY important to getting a car running but I won't even think about driving the car on the highway without it. Getting rear ended by a truck with 18 wheels just gives me the chills.

Grumpy, you need to drug doc one night and slip into his stash for me. I doubt he'd miss just one .

 

I guess I'm still missing something. Are the resistors actually setting "preset" inputs for sensors and posibly an RC network for PW output?
I'm missing how a resistor can do this if the ECM is completly offline.
Any clarification as to what is actually happening.
TIA

 

There is a RFD.
Redunant Fuel Devise.
It's a analog chip, that uses the resistances to develope a PW, when the processor is off line.
Think of it as just a timer, that uses the resistances to set the time periods.

 

I guess you really don't know Doc.
He's real posessive.
Happy's still waiting for a few fingernails to grow back over the French Fry Incidnet.

 

Thanks Grumpy, that helped.
And I thought Doc was the nice one!