MembersPage/GergelyLezsak/SoundCardTrigger

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?

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?


2k7 pulldown recommended on trigger input when driven from soundcard

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 pullup resistor making a DC-offset of 5V : (2k7 pullup by default for HALL-type trigger)

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 HALL-input(s) to ground of 2k7 .. 10k. This worked perfect on my EeePC? 900 and other laptops that weren't working before.

--Tomvl