bumcrack

err .... right
What is it?
What does it do?
What's the point?

john banks

What is it? - a fast acting precision digital voltmeter
What does it do? - measure the output from the lambda sensor
What's the point? - it estimates the ratio of air to fuel in your engine which tells you if you are rich or lean. Useful after you crank the boost up to check you are not going to blow up your engine. Same principle as a Lambda Link. Virtually essential on more than a mildly modded car.

bumcrack

I see

Thank you.

mutant_matt

John,

Quick question, I've built it and have powered the circuit with a 12v transformer. I have adjusted pot T2 until Pin 4 is showing approx 700mV (measured with my DVM, negative on the negative transformer output and positive on Pin 4). Pin 8 is also showing the same voltage and this is also the input to one of the 2 bottom pins on T1 right? The other bottom pin one goes to Pin 7 and the top Pot pin goes to Pin 6?

This is how I've wired it up and the voltage on Pin 6 doesn't seem to change from the 700mV (as I set it on T2), regardless of where I set pot T1.

Have I done it wrong, am I measuring it wrong (wrong place? (I don't think so)) or am I just dense???

Help,

Matt

john banks

There is a fault.

mutant_matt

Thanks John. Unfortunately, I've soldered it all together on a Bread Board so it's a pain to remove (and I did it as compact as poss too so it's about 4cm square )

I'll order another couple of pots and probably another set of components and a solderless BB and try again.

I've checked the circuit out about 10-15 times to make sure it's correct and has no shorts and it's fine. I was hoping to put it in the car this weekend but it looks like I'll have to wait until next w/e now.

Thanks for your help,

Matt

mole

Sorry for being thick but....

T2: One connection goes to Pin 8, One to Ground, where does the other one go??

Also, how do I simulate an input?

mutant_matt

mole,

The "top" (or middle on some pots) pin goes to ground, one goes to Positive and the other goes to 4, 8 and one of the inputs on T1.

Test procedure is a couple of pages back but I *think* you use a 220K pot connected to a 9V battery and use the output of this as the input to Pin 5.

I did that from memory That's how many times I checked my circuit before dedciding I had a dodgy component.

John, I've made up another one on a solderless bread board which seems to work OK (in testing at least - will try and get it on the car at the weekend). I've got Pin 4 to about 704mV and Pin 6 to about 896mV - can't seem to get them closer than that...close enough?

Also, the Lambdalink with remote LED's is about to become available so I may not have a need for this anymore, typical I will plumb both in even if it's just to compare the accuracy of my one vs the Lambdalink.

Ta,

Matt

mole

Thanks for replying.

Managed to "borrow" a few 3914s, bar graphs and bread board from school, just couldn't find any 4k7 pots - will 10k pots be ok to use? (I can't remember much about electronics - although im doing a-level )

If not I'll order some.

Thanks

john banks

4k7 pots are under 20p each from Maplin IIRC. Using 10K may work but the voltage adjustment ranges will be different and you may not get the 700-900mV zone you require. No harm in trying though.

john banks

BTW, one connection on T2 is left unconnected! Middle and one side are connected as shown in circuit diagram - so you could certainly use a 10K pot for this one.

mutant_matt

John,

16p mate

mole - School????

RE: T2 - Dooooooohhhhhhhh!!!!!!!! I thought that went to positive - perhaps that won't make any difference or perhaps it might enable me to get to the required voltages....I just can't get there and I defy anyone to get closer on my board

What a plank hey? Build an EBC - hhmmmmm - perhaps once you've done all the hard work m8

I've already ordered the Lambdalink and it has a much nicer LED set in a nice ally surround (and is accurate without my "old fogey" ( ) unsteady hands trying to set it up).....

Matt

mole

Matt - That's right school! Remember it??

Both me and me dad post under this name, he's the one with the scoob

Was actually your Paint skills that mis-led me john!

Will draw up a track layout on PCB Wizard tomorrow and get it etched!
I found some 5k pots, so will try them.

Thanks
Richard

howardb

10K pots will do, as they cover 4k7. However, you'll have less resolution in your movement.

Another point is that pots come in Linear and Log, stick with the linear ones.

john banks

Thing is Howard one of them (T1) has all three legs connected so the parameters will change.

Lets just pretend I calculated them carefully rather than buying a selection and posting what worked well Too many interdependent variables to work out easily off the datasheet. There was a way of doing it without changing the LED brightness with a few extra bits on the datasheet.

Scott.T

iTrader: (2)

The Center tap of T2 goes to ground hence the line underneath it on the diagram. One pin goes to the chip, the other stays disconnected.

DJ Dunk

iTrader: (5)

[Edited by DJ Dunk - 1/10/2002 12:41:29 PM]

mutant_matt

Scott,

I know that now.....

DJD,

Matt

john banks

I cannot draw. Or paint. Never have been able to. I am not a very good driver also.

mutant_matt

Finally got there properly. Removed the "extra" positive connection and now I've got pin 4 @ exactly 700mV (well my DVM doesn't give me more granularity than 1mV and pin 6 is now 900mV. So John, mine is now more accurate than yours m8








Matt

john banks

No m8 - tell me what it is running in a week. And if it is still dead on without one or other being 1mV out then you are more accurate. But I wouldn't expect any more deviation than that May not look pretty, but this seems to me as accurate as required for an intrinsically inaccurate sensor which is highly temperature dependent and we are reading out of its best operating range.

mole

Drew the track layout on PCB Wizard, and will be etched for tomorrow!

Just got to solder in components - have found 5k pots!

Cheers lads!

john banks

Is this a "project" for your 'enjoyment' or for school? Could make a nice one. If you want any ideas for the write up/design briefs etc I could give you a few ideas, and some useful web links to show how you got to this design. Or is it all for the love of Scoobies? Between you and me I had a nasty habit of getting straight A's at school, so I know what they look for

mole

John, nah this is for 'enjoyment' only - for my dads scoob.

Im actually making a turbo timer as my project, only thing i could think of at the time, never thought of an AFR!!

Thanks for your offering your help though.

mutant_matt

John,

In and working last night. Will take some "proper" readings tonight to see what's going on in there

Will be interesting to compare to Lambdalink when that arrives....

Matt

catflap

When you going into production to sell it to us lovely scoobynet people for 20 notes

[Edited by catflap - 1/15/2002 5:10:15 PM]

john banks

It wouldn't make me any money and I don't have the time, expertise or inclination to produce this on a commercial scale.

A good DIY idea doesn't translate into an automatic business unfortunately. Best kept open source and DIY in my opinion.

Same will be the case for my boost controller which is soon to be tried live when I get the solenoid driver. Circuit designs and code are about 80-90% there for initial testing.

hackish

There is a good wideband DIY sensor you can build for about $200CAD. Open-source type concept as well.

http://www.techedge.com.au/vehicle/wbo2/default.htm

IMHO these narrow band sensors are next to useless. Under non-cruise conditions you should always be running richer than 14.7 so all your gauge will show is that you are richer. Since your engine isn't madly detting and blowing apart you should know this anyway.

-Michael

john banks

It will give you an estimate of AFR even if the narrow band sensor is outside its stoichiometric range if you are careful as to when to take your readings. I'm sure Bob Rawle (Link mapper extraordinaire) said he gets similar results mapping with a narrow band compared to a wide band. There is at least some correlation with results on a proper gas analyser.

Wideband sensors are expensive and have a limited lifespan, but obviously a more accurate result - it is just if that accuracy is worth much on a lightly tuned engine that is all?

As part of an overall monitoring package even a cheap meter like this one has its place.

Using this gauge would tell you if you are running say 3% CO at WOT even if you can't hear any det.

hackish

That DIY link uses a honda sensor. We all know how hondas last forever. I think the sensor is less than $200CAD. That's about $10US (Canada/US joke) or slightly less than 100GBP.

-Michael