serious problems with gauge

[kekso22]

Hi,

I have bought a VEMS Wideband/EGT and after installing it in my car, I found some strange behaviour:
1. The display was switching between the various modes automatically (from lambda to afr to °C to Fahrenheit to rpm …) about every 3 to 4 seconds. Pushing the knob did nothing.
2. The RS232 connection did not respond.
3. The rpm display makes dips in 5 to 10sec intervals to 100rpm.

After this I uninstalled the gauge and put everything on my desktop where I can use professional equipment like power supply, oscilloscope and function generator.

I found out the following:
Ad 1: The malfunction of the display is caused by interference either by power or by RF. On my desktop it works. I think I can fix this.
Ad 2: If I use the Megatune2.25 from the download “NEWround2007_04_25” then the serial connection does not work. If using Megatune2.25 from “OLD_RoundFirmware01” then it goes! Very strange; to check this it takes me 5 hours!
Ad 3: The rpm display (gauge and Megatune) still make dips independent of voltage level (TTL or 12V), duty cycle or frequency. Tuning with pullup on input 11 does not help.

The most serious problem I found is the not working analog input. It gives always back the value zero (variable miscADC) independent of the connected input voltage (0 to 5V). I can measure the 4V pullup on the input as described.
The analog input is very important for me, because I want to datalog the boost value of my car beside EGT, AFR and RPM. This was the reason why I decided to buy this gauge.

What is wrong here? Can it be that I don`t have the latest firmware? Or is my analog input damaged, although the EGT and AFR is working?
I have enough experience to repair the gauge by myself, but then I need information how to open the housing, and a detailed circuit diagram.

Best Regards,
Emil

[Maff]

Hi cant comment on 1) or 2) as ive not had any similar issues.

3) Yup mine does the same, we've had some discussion about exactly whats needed to fix it, have a look here: http://www.vems.hu/wiki/index.php?page=MembersPage%2FMattBushell  The latest firmware lessened the problem, but it still exists.

4) It took me a while to realize that the default settings in Megatune that comes with the gauge are wrong for the misc in.
Get a copy of Brays Terminal  (termv19b.zip), connect up to the gauge (19200 N81) and sent the letter "A", it will return a bunch of bytes with all the data from the gauge, IIRC bytes 16 and 17 are misc in (word data) you should see it change, i have the AFM voltage hooked up to mine.

Worth noting you need to make sure you get a good earth to get usefull data.

[rob@vems.co.uk]

Emil,
Sorry to hear about these problems.  The reason that the display is changing is because the analog voltage is going a little too high, this is a result of the earlier firmware and not having a resistor connected like so:


If you use the MegaTune from “NEWround2007_04_25” then you need to use the firmware that comes with it.

What size pull-up did you use? Can you measure the voltage offset on the ground without the pull-up and guage connected?

The gauge is unrepairable, opening the case will break things - its been designed it to be tamperproof, and if it is genuinely broken can be replaced.

Rob

[rob@vems.co.uk]

Some words were written on the Wiki last night regarding this:

http://www.vems.hu/wiki/index.php?page=AfreshTiny%2FAnalogInput

[kekso22]

4) It took me a while to realize that the default settings in Megatune that comes with the gauge are wrong for the misc in.
Get a copy of Brays Terminal  (termv19b.zip), connect up to the gauge (19200 N81) and sent the letter "A", it will return a bunch of bytes with all the data from the gauge, IIRC bytes 16 and 17 are misc in (word data) you should see it change, i have the AFM voltage hooked up to mine.

Hi Maff,
I have tested with Brays Terminal and get 14 bytes with "A":
"FF FF 00 00 00 48 04 24 00 00 00 00 00 4D"
as defined in Megatune 2.25. No byte is changing when varying the analog voltage!
I think my next step is downloading new firmware. I will post.
Thanks Emil

[kekso22]

Some words were written on the Wiki last night regarding this:

http://www.vems.hu/wiki/index.php?page=AfreshTiny%2FAnalogInput

Hi Rob, Hi Maff,

excellent, the link above exactly describes it! After updating the firmware I get now 30 bytes with "A" command.
Changing the offset to 22 will read the analog input.
By the way the RS232 will work now with Megatune.
Still to find a workaround for the RPM dips. I will play with this and post.

Thanks for the detailled answers!
Emil

[rob@vems.co.uk]

Any info you can provide on the RPM dips would be great, especially the car's tacho line voltage (with gauge disconnected - measure the voltage between tacho line in and ground).

[kekso22]

Any info you can provide on the RPM dips would be great, especially the car's tacho line voltage (with gauge disconnected - measure the voltage between tacho line in and ground).

Hi Rob,

the gauge is just in front of me on my desktop. I am feeding the RPM input with my function generator. Nothing else is connected. The dips come sporadic. Sometimes the RPM display is stable up to 20 seconds, sometimes they appear after 1 second. The input signal and the pullup resistor on pin 11 has no influence on the dips. The dip shows a RPM which is about a factor of 2,5 lower (2205 instead of 5555rpm or 1151 instead of 2860 ...). I think the dip is not a problem of the input signal, it must be a firmware problem (missing int or something like this).
To understand more of the analog and rpm input, a schematic would really help. I haven't found one on the wiki.

Thanks Emil


 

[rob@vems.co.uk]

You've got the newest firmware and you're using the signalgen.exe to create the test pattern?
If so can you tell me the settings so that I can report this and get it sorted?

Cheers

Rob

[kekso22]

You've got the newest firmware and you're using the signalgen.exe to create the test pattern?
If so can you tell me the settings so that I can report this and get it sorted?

Cheers

Rob

Hi Rob,

I have the newest firmware (round_2007-04-25). I don't use signalgen.exe. I feed the rpm input with a square wave signal (0 to 12V/ duty cycle 50%) from an external generator.

Cheers Emil

[rob@vems.co.uk]

I've fed this back to the team: http://www.vems.hu/wiki/index.php?page=AfreshTiny%2FRpmInput and have brought their attention to it, so with luck they'll be able to replicate the error and find a solution.