Who here knows anything about the CIS Lambda box? Any other EE's here?

[mnewport]

This is probably nuts, and I apologize in advance but this subject will be way over most people's heads.

For kicks this evening I pulled apart my CIS box (my interior is in pieces while I install a new headliner). Truthfully I was looking for large value electrolyic capacitors that may need replacement (these things don't age so well, and after 27+ years it would be wise to replace them). While I did find one, I also managed to dissect the circuitry. Lo and behold, it's a simple A/D converter circuit built around an LM2901 quad comparator. From what I can tell it uses a resistive divider/ladder type system (those look like precision Holco resistors to me) to create a scaled set of voltage references for the comparators.

Since I happen to be an electronic engineer whose area of expertise is A/D converters (granted I work with delta sigma but still) my curiosity is piqued. Just wondering if there are any other EE's on this board with any thoughts.

My initial reactions was to look for a more modern, better performing quad comparator and replace that 100uf electrolytic because it probably hasn't aged well. The LM339 is a pin compatible equivalent, but small signal response time is exactly the same as the 2901. So scratch that. The bulk of my personal research and patents I hold (the way I've made most of my money that is) has been in dealing with noise and EMF issues within converter circuitry. I have some theories I may tinker with over the next few days to see if I can get any results or performance improvements (however minor).

Anyway, I may be wasting time but experimenting with this stuff is something I enjoy.

[HawgRyder]

If Fairchild or other man makes a Shottky type replacement...it would be more immune to RF or EMF.
Bob

[mnewport]

Since this circuit is a two bit (from what I can tell) flash ADC, my thought is to look at aspects of the input filter performance as well as maybe explore the performance of the input amplifier (or lack of one?). It's really a clever approach though, as a flash ADC has remarkable speed.

Flash ADC's can be susceptible to a back-fed noise of the comparator towards the reference ladder, so a low impedance amplifier to drive the input might be helpful. I'm sure the good folks at Bosch probably took all this into consideration, but we have the benefit of technology that wasn't available 30 years ago. I know they're using a passive low pass input filter with a cut-off of 1Hz to attenuate whatever input noise might be fed from the sensors.

The direction I typically take regarding EMF in any logic or conversion system is to utilize a theory developed by Philips' EMI engineers. It involves limiting the physical noises created by current movements as logic states switch high and low. Granted our two-bit system doesn't exactly run at high speed but I'm going to tinker with it anyway. If I can find a schottky device I'll look into using it.

Given all the aftermarket substitutes that exist for CIS I'm sure this will all be pointless but it's fun for me. I'd love to hear anyone else's thoughts.

[HawgRyder]

You might also try the old back to back diode limiter trick..to get rid of spikes in the input.
Bob

[mack6820]

You are dealing with 80's technology. Computers didnt even exist then. Maybe you can patent something better?

[Lorenfb]

"it's a simple A/D converter circuit"

Not really! The Lambda control unit operates as analog device which changes the
duty cycle of a switching transistor that controls the frequency valve affecting the
control pressure of the fuel distributor, i.e. To affect the fuel mixture control.

[mnewport]

You are dealing with 80's technology. Computers didnt even exist then. Maybe you can patent something better?

They did exist, they just weren't as fast or inexpensive to implement. I don't really want to develop a replacement system, since there are tons of aftermarket alternatives already. My hope is to find a simple and cheaply implemented improvement that anyone can utilize.

[911freek]

I had my own radio shack, TRS-80 with 4Kb RAM and a cassette deck in 1981....
It was rare indeed.