Labradar recoil trigger DIY

I'll be interested to hear your progress/progression... I live in Canada and no one from the US will sell an inertia trigger for LabRadar outside the US.... Making one is my only option... Keep us posted... Thanks..

Tagging in. Interested in what you discover.

Following

Joining this thread late.

Could provide links to the switches?

Picture?

I assume based on the use of a 1meg pot that the current required to trigger is negligible.

The fancier way to do this would be have the shake switch fire a monstable flipflop with a ~1 sec pulse. That would give a very reliable signal, but a lot more work than it's worth. A parallel rc across the input might accomplished as much. Then again the output of the switch may be very clean as to not require any smoothing. And the LR itself may take care of rough looking signals internally. Love to see the waveform of the signal from the switch.

I love tinkering with simple circuits. I don't need this but may build it anyway just for the fun of it.

Very cool. Much cleaner waveform than expected. I need to get a scope. A monostable flipflop would be ideal for a clean single pulse, but I'm going to try it with just an r/c across it to smooth it out some. Got to finish my third generation primer counter this week, the this will be my next project.

Thanks so much for sharing.

Now that the primer counter is put to bed for a while:

I got the "medium" detectors. Put one on a breadboard. (lower right hand corner) I was surprise that it works in all 3 axis. A plus for sure. Having played with it for a while, my thoughts are:

1) - I'd guess the LabRadar people put in their circuit the ability to smooth out any spikes or rough portions of the signal transition (from off to on).
2) - Rather than worry about spikes/noise I wonder about the length of the pulse. Is it long enough to provide a reliable signal every time?

Many ways to handle that with active circuits, but again maybe just a little RC to insure reliable functioning.
I don't have a scope though I've added one to my Amazon wish list.

[So cool these days that everything is palm size, USB interfaced. My TV went from a 20# wall mounted 20" monstrosity to a thumb sized, USB device that appears as a window on my 27" monitor. I can have from a 5" to a 27" picture any time I want.]

Next best thing is to record a video of it. (I mean duh, I retired as a video engineer.) Yes, I'm only getting 1/30 of a second resolution but better than nothing. Well it turns out 1/30sec isn't enough resolution. The pulse is only one frame long at most.

Next step will be to break out the LabRadar and do some measurements. What is the trigger voltage, possible the minimum pulse width and the current draw of the trigger. Then I'll pick values for a simple RC circuit. What I may find is this is all for naught and not needed. Just connect the sensor directly to the LabRadar and be done with it. More later, but this darn shooting stuff is keeping me busy right now.

To specifically answer with a waveform generator, hopefully one that will allow single pulse at a time. I'm looking at waveform generators and scopes right now. I've been out of the home experimenting hobby for a while and debating how much to spend on these. The old name brands are so expensive and I'm hesitant about the plethora of Chinese brands. Also gonna check with my old work, I'm pretty sure they'd loan me a scope for a couple of weeks. This may take a while. Especially (notice how I'm bringing this back around to shooting?) with all the matches that got pushed from spring/summer to fall.

BACKGROUND DISCUSSION - SKIP IF YOU DON'T LIKE WAR STORIES

Electronics has always been an occupation and an avocation. Work consumed my time the last 20 years and I did away with most of my home parts and meters. One of my ideas for old age is to start playing with things electronics again, specifically the microprocessor boards like Rasberry Pi. LabRadar has given me a starting point to buy some test gear. If you're at all interested. My job during the summers in HS was to maintain the head-end and to teach installations (drops) for an early analog cable TV system. USAF I was Avionics tech (Autopilot) on the C5A test team. Earn my 1st Class FCC Commercial license (when they had those things) and a mail order degree in TV Production while I was in the AF. Later added the Extra Class Amateur license (W4ADS). Retired 2 years ago as a Video Engineer and Lighting Director for a large venue in town.

Just to remind folks. LabRadar can activate it's "recording" either by hearing the sound of the shot through it's internal microphone or by watching for some moving object in its "field of view". The later, called Doppler Trigger, isn't as reliable and you may miss the closer in velocities. The microphone can trigger falsely if there are other shooters nearby. LabRadar has an 8 step sensitivity setting than can help ignore extraneous sounds. There is an external jack which can be used as a trigger in place of the internal mic. So that's what is being tested, the external trigger input. Exactly what does that external trigger look for and what parameter are required to make it work reliably?

The first step is to see what LabRadar needs to work, measured in two parts; Amplitude (voltage) and Duration (pulse). I got my variable power supply this week so I've done the amplitude tests. My function generator isn't due in for another month so that test will have to wait.

Here are my findings of minimum trigger voltage for each trigger level. I verified the voltage setting with an independent DVM. I only have one Amp meter but the readings are basically insignificant current draw.

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

Current draw, btw, is a function of the actual voltage used to trigger, not the level setting. The current draws are insignificant. Any external circuit will need to make sure it drains itself before the next shot. Not a problem with a straight switch but could be with an external mic circuit.

Okay, now we know what LabRadar is looking for, amplitude wise. Next step, when my function generator gets here, is so see how sensitive it is to pulse width.

The ultimate aim is to build a reliable circuit for detecting recoil as a trigger which would be useful for silenced devices and quiet airguns. I might also look at an external microphone, specifically one that is more of impulse pressure switch than a true microphone.

What would a thread be without pictures. SIMPLE, yes, but it makes it funner. The breadboard is just used to hold a little switch for the test. I point the LabRadar at a fan during the test. Gives it something to "detect" and resets it for the next activation. My desktop fan gives me readings between 550 and 800 fps. Lousy SD.

Yes, results will vary with unit because in general electronic components, have around a 10% tolerance. You can pay more for higher tolerance, but usually it's not needed for something at this level.

I'd think 1.5V at level 5 would be an excellent choice.

More adventures with electronics, LabRadar and S-H-O-O-T-I-N-G

Boring discussion of a function generator.

I didn't want to spend $125+ on a lab function generator, so I bought a $25 Chinese "module". It arrive much sooner than I expected. It goes under the brand name of Caredy. It was shipped in a small plastic envelope. No padding and NO instructions. As expected it does the bare minimum which is square wave in either a continues stream or in a specified number of pulses. The later is what I really wanted for this project and that was the ability to produce a single pulse of varying width. It has limitations, only up to 150Khz continuous and only down to 1/1000sec pulse width in single pulse mode. However it does what's needed for this project. they say 1% accuracty, but my voltage readings put it a little be further off than that. e.g., the 3V setting only produced 2.78V. But that can be accounted for. Don't have my scope yet, so can't measure the accuracy of the pulse timings. At higher levels, >2V, current draw does cause a slight change in voltage output.

Click to expand...

What I was measuring today is the minimal pulse width needed to trigger the LabRadar. IOW, if a shake switch only produces a contact for 0.1 seconds will that be enough to trigger the LR?

I was limited in that my pulse widths can only go down to 0.001 seconds and my voltage only down to 0.87V, but that seem to be right at the limit of the LabRadar. It's enough to make a good guess as to what would be a reliable pulse. Here are the settings.

Levels 1-5 worked reliably down to 0.87V and 1 milisec. Couldn't go any lower. Probably close to initial tests above.
Level 6 worked down to 1.6V and 2ms
Level 7 worked down to 2.1V and 2ms
Level 8 worked down to 2.8V and 5ms

Longer times at lower voltages produced only slightly different results and neither did higher voltages cause shorter times.

So my conclusion to be sure of an external switch working I'd use the full 3V provided by the LR external jack, select Level 5 and make sure the switch produces at least a 10ms dwell time. I know this isn't an eotwawki thing. If you miss a reading or two not a big disaster.

Next step, when the oscilloscope arrives is to measure the dwell time of the shake switch. Probably on an airsoft gun, a springer air gun, a live firearm or two. It might also be interesting to be thinking about an external microphone down the road.

Got my scope, an Owan USB 2 channel. It worked with my 7 year old laptop running Vista. Amazing. Easy to use. First order was to check out my function generator to see what type of wave forms it was actually producing. Fairly square. So good for it.




Psst: I know my reflection is in the pictures of the scope, but I’m not so anal to go back and recreate them without the reflection. You’ll just have to suffer with it.

Now to hook the scope to the Shake switch and see what the wave forms look like. Pretty rough. Done with an air soft gun.



I added a 10uF capacitor from the trigger to ground and it did wonders in shaping the waveform.



Or with a short sweep time


I made two plug-in units. One with just the Shake switch and one with the switch and capacitor. Encapsulated them with several layers of shrink wrap.



Needed a good way to mount them onto my guns so I took an old scope ring, cut it up and clamped the assemble to it. Just used a small cable clamp to hold it to the mount. I tried it both axially and perpendicular and there doesn’t seem to be any difference in the waveform. You don't really need to cut the scope ring. I could have just clamped it where the top strap would be.






I also built a break-out block using to 1/8” jacks so I could attach the scope in mid stream without the need for the breakout board. This of course isn’t needed for actual operation.




All told, the Lab Radar doesn’t seem to care about the wave form. At least not with the airsoft gun..The medium Shake switch might give false readings when you cock the gun, or operate the action. Though most of the time it didn’t unless I got rough with the gun. I’m set on level 3 sensitivity, which is what I normally use anyway. I don’t think it much matters, as once the Shake switch makes contact it’s providing a sufficiently long enough trigger for the LR to respond. I used the full 3Vdc from the LabRadar as I saw no reason to step it down.

NEXT and LAST STEP (whew) Since I have both modules, with and without capacitor, the next step is range time. I thought I’d do tests with a 10/22 rifle, a 22/45 pistol and a 9mm pistol.

peels said:

The scope trace of the switch only...why is the peak voltage dropping over time?

Click to expand...

Could be the input circuitry of the LR itself. I imagine they have some input filter (r/c) circuitry.
Of course I'm doing this test with an air soft gun, which is a "springer" and probably represents the worst recoil "action". Not the sharpest recoil but a complicated, back and forth recoil.

I'm in the process of putting everything up, but I might re-test this using both the LR and doing it with just a power supply, no "load".

I don't know if I feel like dragging the scope and laptop out to the range, but I might just for the fun of it. Try this with a real springer air rifle, as well as several firearms.


This has been fun and given me an excuse to buy a scope (albeit a cheap one) for future experiments. Thank you Peels. I've also gotten to know more about my LR's trigger, and while it's never been a problem, that I was aware of, I may be using the external trigger more, especially at indoor ranges.

This is a Shake Switch Only mounted on the air soft gun with an external supply. No LR. I think we're seeing a combination of very narrow signal spikes and contact noise. <no reflection this time>



No matter how you shake it <pun> the Shake Switch has a very messy output. I like what adding a capacitor does to the signal. HOWEVER, I'm not seeing that the LR cares. Probably have their own integration circuitry on-board. Range testing in a week or two.

Guys,

A SW-18010P (most sensitive) soldered onto a female 3.5mm socket. No need for capacitors and resistors as the radar filters the multiple triggers in its 2-second timed pause. Use the tip and middle contacts and ignore the shield/ground.


Do all the loading/cocking before you arm the radar although if it triggers prematurely you can ignore it. If it gives a false reading it is usually obviously different to the string and you delete it; either at the time or later.