Anyone see a problem with this?

[JimBobFett]

For E/X-Mags, I've been using this Hall Effect Sensor for the trigger: Melexis 90217

I'm loving it, but wonder if it could be a problem. Semi = one shot per pull, right? Okay, this is that still... but its a constantly recalibrating sensor; It doesn't have a fixed on or off position. Instead, when you pull it 1mm or more, it turns on, and when it is released 1mm or more, it turns off. Make sense? So no matter where the trigger is, there is no fixed 'trigger on' point or 'trigger off' point, its just '1mm or more in the other direction that you just pulled'. I think its friggin cool to shoot, but is this a 'no-no' in any way?

[athomas]

This could cause a problem with the expanding and collapsing magnet field of the solenoid. The HES switches based on a change in the magnetic field (once the proper amount of magnetic field is sensed) rather than the strength of the magnetic field at any given switch point.

When you fire the emag, the solenoid magnetic field expands or collapses around the HES. Normally, this doesn't affect the operation because the program only senses the pull of the magnet into the HES, and the magnetic field fluctuation is ignored because it is back to normal in time for the next trigger pull. In any firmware version that allows a trigger capture before the solenoid completely resets can be affected by the changing solenoid magnetic field because it can oppose or add to the existing magnetic affect from the trigger. This can cause the HES to go through the on-off range without actually moving the trigger.

In your self calibrating HES, the same issue could occur. If you pull the trigger and activate the HES, the firing of the solenoid will affect the magnetic field around the HES, causing it to be in the changing magnet field. It won't be biased by a permanently installed magnet, so that won't be an issue. Only the changing magnetic field will affect the operation. If you are running firmware that ignores any switch inputs during the solenoid magnetic fluctuation times, then only the initial magnetic value will determine the firing point. After that, only the final position(s) of the trigger, before any change in direction, will be evaluated. The trigger will essentially activate and reset based on movement distance rather than passing a fixed point. A problem might present itself with the changing magnetic field in any firmware where the trigger event can be captured while the solenoid is active. The active solenoid will cause the magnetic field around the HES to change which could simulate a magnetic change equivalent to a reset and pull of the trigger, even though no physical movement of the trigger has occurred.

So, in a nutshell, your HES might work fine for most emag applications. If it is firing properly, without going full auto, then you are probably fine. In fact, it might actually work better, as you have indicated based on your response. You should be aware that it might make an existing known problem worst for some firmware versions. Note: We can correct the known issues by using a capacitor of a known value on the trigger input. I don't think we will be able to do that correction on your HES because it is a hysteresis issue and not a rapid impulse caused by a changing magnetic field.

[JimBobFett]

Ah, this whole time I was thinking "well, if someone WANTED a longer trigger pull this sensor makes that pretty impossible", but you make a good point! Thanks, that's why I ask!

So far, in dry firing, this seems to be okay, but I get what you are saying: I've heard about that, know about the coil's field, yet totally forgot that once it started working.

Scenario 1: trigger is pulled, coil fires and the field generated by the coil causes the HES to think the trigger has been released so once the coil is done firing the trigger is sensed as 'pulled' again and will fire even though the trigger might not have moved.

Scenario 2: trigger is pulled and the coil generates a field in the opposite direction so the HES thinks the trigger has been pulled even farther, but once again as the coil is de-energized, the magnetic field generated could make the trigger sense that it has been released... this would be the desired scenario it seems.

I did shop around for a few other HES's, including analog in case I needed the software to determine the values... just trying to avoid the slight processing lag that using analog inputs causes.

Thanks!