I've been using generated wav files for bench trigger testing for a long time -with success.
Now I managed to have an Asus Eee 900 laptop for tuning, and it seems it has a different soundcard. If I attach the ECU to the headphone output, the ECU jumps to fine rpm for 2-3secs then it loses rpm signal (sometimes with trigger error).
It is the case every time I disconnect and reconnect the audio cable. -I need to disconnect, it's not enough to stop and restart playing from software.
Other notebooks work flawlessly in the very same situation and cables, but this tiny one (eee 900) not.
It's sound is fine listening through an earphone but not for VEMS
Any ideas?
- after loss signal vems is not receive anything? neither after vems reset? Maybe turning of device detection on soundcard out and in can help...
- VEMS power down and up helps also.
I've checked the signal with a scope, and the problem is that vems seems to pull-up the whole signal.
It is normally a square signal between -2V and +2V, but as VEMS is connected (or powered up), its climbing and in a few secs it ending up just below zero (range of approx. 0.5V and 4.5V), since the essence of this signal is crossing zero, now I see why it looses rpm.
I guess this soundcard is isolated with some series capacitor inside which allows some DC bias of the signal(?)
Question: how to solve this problem, -preferrably outside of both vems and the notebook?
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I had the same problem, some sound cards were working, some not. Every sound card I came across has a DC-blocking cap. The VEMS has a 10k pullup resistor IIRC for HAL-type trigger (VR works fine with every soundcard), making a DC-offset of 5v. The clapming diodes will make the peak value 5v, thus making the DC offset effectively smaller, but if the amplitude of your sound card is to small, it will not reach the '0' level.
The solution is very simple: Connect a pull-down resistor of the same size as the pull-up resistor in your test cable, thus a resistor from the HAL-input(s) to ground of 10k. This worked perfect on my EeePC 900 and other laptops that weren't working before.
--Tomvl