Autronic SM4

[0Fen0]

Hi guys, first post; sorry it's a Q but hoepfully someone will help.

I have an Autronic SM4. I bought the Autronic cable to go with my LM-1 so I could Autotune but the Autronic is seeing roughly 10.9:1 AFR when my LM-1 is reading close to Stoich at idle (say 14.6:1).

I was reading the SM4 manual and it now looks to me like it supports a 0-5v O2 input rather than the 0-1v the SMC and SM2 needed.

I can't ask the question on the Autronic forum because they are so precious that you aren't allowed to mention tuning with another wideband, especially Innovate (and even my fantastically helpful dealer just says "Innovate won't work proerly" which is obviously nonsense) so, anyone on here able to confirm? Assuming I'm rigth I just use the analog out cable supplied with the LM-1, right? Anything needed on the Autronic settings or leave them as default (to suit their own sensor)?

Thanks in advance,

Fen

[klatinn]

Hi,

Did the manual specify what voltages on the 0..5V input correspond to which AFR? I know quite a few people are running the SM4 with LM-1 and LC-1 without any problems. Some have even reported that autotuning works faster with the LM-1 than with the Autronic wideband.

Regards,
Klaus

[0Fen0]

The manual doesn't specify voltages explicitly at all; it is pretty clear from the documentation the unit is still very early production.

What got me wondering was that the offset and span they default to is to suit a 0-5v input which I suddenly realised is not the 0-1v the Autronic cable is designed to drop the LM-1 output to.

I guess it's worth a try with the standard analogue output cable - what wires should I connect from it? I guess ground and analogue output 1 to the O2 input on the SM4 but which colour are they?

Fen

[klatinn]

Hi,

Analog out 1 is red. AFIK the ECU you have has differential inputs. So you connect the analog out ground to the - input and the output itself to +.
If you can datalog from your ECU without engine running, you can program the LM-1 analog out to 5V flatline (set both voltages in the setup to 5V) then read the reported AFR from the ECU. Do the same for 0V. If you post those AFR numbers (0V and 5V) I can give you the correct settings for the LM-1, assuming the 0..5V input of that ECU is linear.

Regards,
Klaus

[0Fen0]

Klaus,

That's great. The input is linear so the test should work.

Before I get into chopping out the now hard wired Autronic cable I think I can test the theory as follows:

The LM-1 is set to output AFR as 0v = 10:1 and 5v = 20:1.
The input on the SM4 (by default and according to docs to suit a 0-5v input) is linear with offset=1,000 and span=2,500
Since the Autronic cable is reducing the LM-1 output to 0-1v then I *think* if I increase the span by 500% to 12,500 that should work? Either that or reduce it to 20% (500)?
One of those should give me the right range, right? I realise taking 0-5v down to 0-1v and then fudging it back to 0-5v is a bad plan long term of course but I'd like to prove my point before I go cutting into the loom I only finished building yesterday

[FSAE NZ]

we are using an SM4 also, we just use the analog output cable (not the autronic one) and tweak the LM1 to give 2.6V at 20AFR. After that some trimming on the values in the autronic software and it goes mint... except when the sensor spits...

using the autronic cable will kill the ecu's excellent resolution

[rocketrally]

I use the SM4 exclusively with my LM1.

All I did was the following: ditch the autronic cable. Use the wider resoloution analog output of the LM1.

(the following is VARIABLE in that you can actually set the values to whatever you want, as long as you get the right span and offset)

set the 0v = 10 AFR and the 5v = 20 AFR (or you can use 1v, or set whatever voltage you want). Because I was *unsure* if the SM4 still wanted 0-1v like the SMC/SM2, I used my simple voltage divider circuit on mine right from the start, so really, my 5v output becomes 1v anyways. But the SM4 can take whatever you want.

to find the right 'span' and offset, I set the LM1 to output 5v continuously all the time, at any AFR (with my divider this was really 1v - again, not important) . And looked at what I got in SM4, and played with span/offset until it read 20 AFR. Then I set the the LM1 to output 0v continuously all the time, at any AFR, and played with span offset until it read 10AFR. And then I did it for 2.5v continuously, and played with span/offset until it read 15AFR.

Playing with the span and offset, you can easily figure out numbers that will work for you that will equate to 10AFR and 20AFR with the linear split (but you can use *any* AFR you want for this, and any voltage for this as well). You will also notice that this makes it really easy for the SM4 to read a 'simulated narrowband' setup as well.

Took about 10 minutes to get the right span + offset. I will check on the actual numbers I used, but again, that was with a divider so no real issue.

-Patrick Richard
Rocket Rally
www.patrickrichard.com
www.rocketrally.com

[0Fen0]

Thanks guys; just what I wanted to hear.

Unfortunately I can't get back to the car until Tuesday but I'll get it set up then. Excellent news on the narrowband emulation also Partick as I can then set the car to run closed loop to get through its emissions test.

[0Fen0]

I would be interested in your numbers for offset and span - the Autronic cable is just a voltage divider anyway so they should be close for me in the first instance.

I think I'll change to a straight analogue cable pretty quick though because it must have higher resolution if it's 0-5v all the way than if it steps down to 0-1v.

[klatinn]

the Autronic cable is just a voltage divider anyway so they should be close for me in the first instance.

No it isn't. If it were it would be a ripoff. It has an op-amp differential amplifier inside that uses the ECU ground as reference to eliminate any ground differences between the LM-1 and the ECU ground.
This is basically the same thing as the Autronic widebands do also (special target adjusted ground differential).

Regards,
Klaus

[0Fen0]

I wasn't aware of that. My post would have been more accurate if I had said "the Autronic cable acts as a potential divider..."; that's still true though, yes?

I guess now I understand why it needs power.

[0Fen0]

Just to wrap it up for anyone else with the same question I set the span to 500 and it works a charm. I'll probably switch to the analogue cable in the future but for now I'm happy enough with the Autronic cable.