Growler Wrote:Great post and idea!
Does LabRadar give details on the trigger requirements like voltage thresholds (TTL?), timing, etc? This triggering could be much more reliable than the mic.
I doubt whether you will get much cooperation out of Labradar. A while back I asked for the voltage range limits for the external power source jack and received an email answer saying it was proprietary top-secret information. They sell an external power supply so it's not in their interests to help people make their own.
On another site there are two shooters 'Peel' and 'alsauvre' doing some testing for a DIY recoil trigger and these posts are helpful;
[INDENT]['Peel'] So far, I have figured out that for the stereo plug used for the external trigger 3 sections are voltage supply at the tip, presumed control signal middle ring, and then ground.
I am guessing a voltage proportional to the supply voltage to the signal connection is what is used for external triggering.
[then later he posts this]
I have confirmed that applying 3v to the signal line will trigger the radar to track. I did this by shorting the voltage supply to the signal.
[a few posts later]]
With my labradar, I found that a voltage signal of greater than 0.65v is needed to trigger the unit reliably when the trigger level is set to 1. A voltage of 2.6v is needed to trigger at level 5.
the [vibration] switch will make multiple contacts, but it settles pretty quickly. Pretty sure there are internal voltage comparaters inside the labradar that looks at the voltage of the signal. And it looks like it does not matter if the switch tries to trigger mutiple times quickly...the labradar won't re-trigger until the amber light comes back on after the trigger goes active. That takes about 2 seconds.
['alsauvre'] Here are my findings of minimum trigger voltage for each trigger level.
Labradar trigger Level, Voltage(V), Current Draw (in microAmps)
1, 0.08, 3
2, 0.10, 3
3, 0.14, 5
4, 0.20, 8
5, 0.50, 17
6, 1.50, 50
7, 2.00, 66
8, 2.49, 83
[/INDENT]
They use an oscilloscope to look at the waveform of the vibration switch and then agree a capacitor will smooth the trigger pulse, which sounds like it's unnecessary because the radar has it's own inbuilt filter. My circuit is borrowed from another shooting site so whoever designed that has decided a capacitor is needed. Truth be known you could just use the $1 vibration switch by itself.
So, they are using the microphone jack's own power source (which I understand to be 3V) to provide the voltage required to trigger the radar.