I was doing some searching and came across this thread that talks about WBO2s and someone posted "I'm sorry I posted about the LSU4 prematurely. However, I'm reading that this issue has to do with the sensor heating. It seems some minor changes to the diy circuit can have this newer sensor working. I'm still trying to chase this down. I bought one of the LSU4's thinking it would be good to go. I'm still glad I did. The price is MUCH better than the ones for the Hondas. This sensor WILL work!!! It's just going to take some extra attention up front..." So I took a look at the schematics that are listed on the DIY WBO2 site and downloaded the L1H1 datasheet avalable there. Not much info in it for doing the heating portion. I also downloaded the LSU4 datasheet which has lots of info. I does look like the LSU4 could be used in place of the L1H1 in the DIY WBO2 kit with only some resistor and capacitor changes. Looks like I will have to fire up the simulator in the coming weeks to see what it would take to do this, if it is at all possible. Also, the DIY WB site says that the L1H1 connectors are no longer available. Does anyone know where I could get some L1H1 and LSU4 connectors?? Cheers, J

There was a guy from Europe, Greece IIRC, that early on in the DIY-WB release that did just this. He lowered the heater voltage to 8.8 to 9.0 volts or such and used an LSU4 Bosch sensor.

I really don't see any reason why it won't work. The AFR Vout probably won't match, but as long as that is understood the system will still have utility.

RBob.

The only thing to note, is the NTK is the standard by which all others are judged. Go to any emissions lab, and they're using the Horiba NTK sensor. MOTEC, BIg Stuff, ACCEL, FAST, all use the NTK. There is a reason.

Saying a few bucks can be a good thing, but if you use 3-4 LSUs for every 1 NTK, your not saving any money in the long term.

Just something to consider.

RBob,
Those are the two main things I need to look into and also the start-up current and to adjust for the possible sensor heating element resistance difference. Would you know where there a better datasheet describing the heating element part of the L1H1. I was going read the schematics in more detail to what is going on with the voltage feedback and stuff to figure out how the voltage control on the LT1086 works.

Grumpy,
That is a good point you make. I did post the "It will Work!!" comment but it was a quote someone else made in another thread I was reading.

I just heard back about the DIY WBO2 kits being available in two weeks or so. I planned on ordering two of them. One to use with the L1H1 and the other as a learning tool using the LSU4.

There is a link on the DIY WB site to a place selling the L1H1 for about $200 which seems like a good deal to me. Also, there is readily available code patches that report the WBO2 data via the ALDL. That is a plus.
The LSU4 is cheap so I think it is worth playing with.

J

Interesting none the less.

The DIY-WB circuit has three functions: a soft start, a current limit, and a voltage limit.

The soft start circuit brings the output of the LT1086 up slowly, takes a few seconds for this.

At this point the heater resistance is low (ca 3.3 ohms cold) and the LT1086 is in current limit mode. This is controlled by the 1 ohm resister in series with the output (the 5W jobbie that gets a couple of 15 ohms paralleled on it).

As the sensor heats up the heater resistance increases. This causes the voltage output of the LT1086 to increase.

Once the output voltage reaches ca 10.4 volts the LM431 acts as a voltage limiter against the LT1086. It also turns on the heater ready LED & ISO1 to enable the pump circuit.

(there is a fix for heater circuit oscillation, place a .001uf through .01uf cap across the LM431 pins 1 & 3, outer two. The cap type and value is not critical. The LM431 is the one in the heater circuit).

RBob.

Under what circumstances is it necessary to apply this fix, how do we know if there is a problem? (or does it affect all diy wbo2's universally and should be applied universally)?

This ECO (engineering change order edit; I had a small grin in here, but it didn't show up, try again: {g}) should always be applied. There is no down side to the addition of the capacitor. It really is required on the DIY-WB. Not too bad for a hobbiest designed unit, only one minor change.

Without the capacitor an oscillation in the heater control can show up at any time. After a while I was finally able to replicate the problem on the bench. It has to do with noise on the B+ feed. Just need to decrease the feedback pole frequency a tad and the problem goes away.

RBob.

P.S. this fix was discovered by someone else, not me, but I did check the result and it is valid.

I downloaded the datasheets and studied the ckt for a few nights. That is exactly how it works. The 1K resistor and the shunt regulator keep the voltage constant. My model shows that the voltage ramps up in only 5 seconds because I don't have the load changing resistance as a function of time (current)....have to fix that.
The cap between pins 1 & 3 makes sense......to by pass the gain for high freqs so that the output doesn't react to it.

J