Labradar Recoil Sensor

[Klem]

Guys,

Those with a Labradar shooting suppressed or close to others on a firing line might find this useful. Changing the Labradar switch from sound to recoil. You can use doppler with suppressors however how far from the muzzle the bullet enters the emitter arc is anyone's guess, which makes extrapolating back to the muzzle another guess.

You can buy these recoil switches from a couple of sellers in the States. They come in rectangular plastic boxes however if you DIY you can get a smaller form factor which is more suited to Picatinny rails . If you can solder electrical parts then this is an easy circuit. If you already have the soldering iron and glues it'll be less than $10.

You need the following parts:

1. 3.5mm plug and cable
2. 1.5K ohm resistor
3. 100nF capacitor
4. Vibration sensor (SW-18010P)

Notes:
There are three switches in the series from most sensitive to least sensitive SW-18010P, SW-18020P, SW18030P. The 18010P is the most sensitive and I recommend you get this. If the radar is 'armed' when you load up the gun it will probably trigger and you get the 'WTF?' screen (no bullet), which you just ignore and go ahead and shoot. It is better that it triggers on being loaded/unloaded than not being sensitive enough to trigger on every shot. I tried the 18020 sensor and it works on larger calibres but one or two shots in a 15 shot Grendel series did not trigger. If you hold the gun firmly then there's a chance the less sensitive switches won't pick up every shot. The most sensitive switch is the go however: the 18010P.

Be careful of the thin lead coming out of the sensor, it is pretty fragile and I've broken a couple off. To prevent this I'm using a piece of project board with two holes where you solder the thick lead and this supports the thin lead. Or you can just be careful.

I figure if the sensor is at right angles to the barrel axis it stands more chance of picking up recoil. From what I can gather it is a wobbly coil surrounding a fixed post.

I prefer the UTG rail cover version as there's no need to screw it onto the rail. It slides on and off and won't come loose. Also no need for a hex wrench. The bubble level form factor is pretty tiny however so it slides under a scope on a bolt gun where the UTG rail cover won't fit.


The circuit diagram and the idea of using those cheap Chinese bubble levels (EBay) is adapted from James Elphick on ozfclasforum.com (2017). I came across a 3.5mm cable which had different colour codes to his diagram so the circuit diagram here is generic.

[D.Davis]

Thanks Klem, good stuff.

[Growler]

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.

[Klem]

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;

['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

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.

[FRB6.5]

FWIW if using the adafruit vibration sensor switches no capacitor or resistor has been needed in my experience. I've been using mine that way for about 20 months.

https://www.digikey.com/catalog/en/partgroup/vibration-sensor-switches/68699

I prefer the medium switch, I can trigger the fast with just hand tremor. Dropping the bolt on any semi will trigger it, so I do that first then arm the Labradar.

I use a loop of shock-cord with a plastic cord lock to attach the sensor. I typically will put it on the scope tube or bell but I can attach it anywhere; hand guard, bipod etc.

For a simple enclosure and to ease assembly I used a 3.5mm 3 pole stereo male plug connector. It is still fine soldering but a heck of a lot easier than going wire to wire and it makes for a pretty sturdy package.
It also allows rapid changing of the switches if you wish to have one of each sensitivity for different tasks (fast for air gun, slow for a .50 etc.).

This all being said my time is valuable enough to me I wouldn't make them and sell them for what https://pietrecoiltrigger.com/ charges. I had all the equipment and components on hand except the switches so it was an inexpensive project for me to try.

EDIT:
One other point on why I arm after closing the bolt. As Klem noted a false trigger can give a "failed to track projectile" error. That one is no big deal, BUT, it can also give a random velocity reading as well. That one is a big deal if you forget where in a string it happened and don't delete it or delete the wrong shot. Piet has video of this issue on his site.

[Klem]

FRB,

The vibration switch I am using is the same design as your Adafruit; a movable coil surrounding a rigid post. The numbering is the same in the photos on Adafruit's website.

On the other forum they mention the wobbling coil of these switches makes and breaks contact several times before settling down. This triggers the radar only once however in a 2 second period which is what you want. By the end of 2 seconds the vibration switch has calmed down. I agree, you probably don't need the capacitor to smooth the impulse, or the resistor as it uses the voltage from the radar itself.

I'll give the switch by itself a go.

What have you done with the wiring of three leads to two?

[FRB6.5]

For direct solder to a audio plug cable with a pigtail I used the tip and ring leads; red and white. I just cut the black sleeve wire flush and insulated the end with hot glue while squirting some around the switch leads to insulate then covered with heat shrink tubing. (The colors can vary with china made cables so verify which are tip and ring with a multi-meter.)

For use with the solder on plug connector tips I use the center tip connector for the stiff post lead (which is also in the center of the switch), and the short ring lead for the thinner coil lead. The longer sleeve connector makes for a clamp to hold the switch body with a little bending of the end then gentle squeeze with some crimp pliers. I trim the leads short enough to fit the switch body inside the plastic cover then fill the gaps with hot glue to insulate and hold it all in place after soldering.

I have 3 and 6 foot male to female audio extender cables I use these plug modules with.

[Klem]

FRB,

So you are leaving the Ground/shield cable untouched? Fair enough - I can see how you don't need it.

The solder-on plug connector you talk about to is a 3.5mm female socket? So the cable connecting the radar to the gun is a standard male-to-male plug lead? If that's case I can see how that makes moving guns easier than my settup where you have a lead fixed to, and hanging off the gun.

[centerfire]

FWIW if using the adafruit vibration sensor switches no capacitor or resistor has been needed in my experience. I've been using mine that way for about 20 months.

https://www.digikey.com/catalog/en/partgroup/vibration-sensor-switches/68699

I prefer the medium switch, I can trigger the fast with just hand tremor. Dropping the bolt on any semi will trigger it, so I do that first then arm the Labradar.

I use a loop of shock-cord with a plastic cord lock to attach the sensor. I typically will put it on the scope tube or bell but I can attach it anywhere; hand guard, bipod etc.

For a simple enclosure and to ease assembly I used a 3.5mm 3 pole stereo male plug connector. It is still fine soldering but a heck of a lot easier than going wire to wire and it makes for a pretty sturdy package.
It also allows rapid changing of the switches if you wish to have one of each sensitivity for different tasks (fast for air gun, slow for a .50 etc.).

This all being said my time is valuable enough to me I wouldn't make them and sell them for what https://pietrecoiltrigger.com/ charges. I had all the equipment and components on hand except the switches so it was an inexpensive project for me to try.

EDIT:
One other point on why I arm after closing the bolt. As Klem noted a false trigger can give a "failed to track projectile" error. That one is no big deal, BUT, it can also give a random velocity reading as well. That one is a big deal if you forget where in a string it happened and don't delete it or delete the wrong shot. Piet has video of this issue on his site.

I've had the Piet recoil switch for two years. The false readings are easily distinguishable by the large velocity discrepancy. You can adjust the sensitivity of the LabRadar to reduce the false readings too.

[FRB6.5]

FRB,

So you are leaving the Ground/shield cable untouched? Fair enough - I can see how you don't need it.

The solder-on plug connector you talk about to is a 3.5mm female socket? So the cable connecting the radar to the gun is a standard male-to-male plug lead? If that's case I can see how that makes moving guns easier than my settup where you have a lead fixed to, and hanging off the gun.

Repair plugs like these:

https://www.amazon.com/gp/product/B077XS77FG

and cable like these:

https://www.amazon.com/gp/product/B0793L5343

I suppose similar female adapters would work, but may not have the room under the plastic cover like the male do. The Switch can be made to fit inside easily.

[Klem]

Repair plugs like these:

https://www.amazon.com/gp/product/B077XS77FG

and cable like these:

https://www.amazon.com/gp/product/B0793L5343

I suppose similar female adapters would work, but may not have the room under the plastic cover like the male do. The Switch can be made to fit inside easily.

Yep, I see what you mean.

Correct, I was thinking the reverse, with the female socket and sensor on the gun. I think there will be enough space https://www.altronics.com.au/p/p0084...o-jack-socket/

[FRB6.5]

I've had the Piet recoil switch for two years. The false readings are easily distinguishable by the large velocity discrepancy.

Not always, especially with lower velocities such as from a Grendel with a short barrel. I've had false readings withing 200 FPS, close enough to look plausible but wrong enough to wreak havoc with the data.

I just drop the bolt then arm. It has been perfectly reliable this way.

[FRB6.5]

On another Labradar reliability tangent; Bluetooth.

If using an external battery the quality and wire thickness of the USB cable used does affect Bluetooth. I believe it may have been mentioned on the forum before but I can confirm the cable does matter.

I had a short, right angle USB cable so it wouldn't get tangled and to reduce chances of snagging or damaging the socket. The cable was on the thin side. While I never had any other issues with the Labradar's function ore reliability, Bluetooth was erratic at best. I switched out to a longer, very thick 24ga. USB cable and Bluetooth was rock solid, it didn't drop a single time over a two hour period.

[Klem]

On another Labradar reliability tangent; Bluetooth.

If using an external battery the quality and wire thickness of the USB cable used does affect Bluetooth. I believe it may have been mentioned on the forum before but I can confirm the cable does matter.

I had a short, right angle USB cable so it wouldn't get tangled and to reduce chances of snagging or damaging the socket. The cable was on the thin side. While I never had any other issues with the Labradar's function ore reliability, Bluetooth was erratic at best. I switched out to a longer, very thick 24ga. USB cable and Bluetooth was rock solid, it didn't drop a single time over a two hour period.

Never had any Bluetooth issues other than the connection dropping out when the IPhone goes to sleep...all too often. My lead is at least 1M. Are you thinking the thin lead was not shielded and it was RF interference? This is the lead I use, a 24AWG


Do you think the radar will take 8.3V via the USB port? In the picture you can see the DC: DC voltage regulator in between the Li-ion battery and radar. The regulator drops the fully charged Li-ion pack from 8.3V to 5V. Surely there is an internal regulator in the radar. The internal battery compartment takes 6 x 1.5V AA in what looks like series = 9V so I'm tempted to try 8.3V directly from the battery pack.

[FRB6.5]

I'm pretty sure it requires 5V only over USB. There are reports of some newer multi-output voltage USB batteries damaging labradars.

As to the Bluetooth it's possible it was RF but I think current limiting may have been in play as well. I recall having issues getting a cellphone to charge using thinner USB cables in my car, changing the 12V to USB adapters had no effect. Once I used the original USB cable, bam it worked as expected.

EDIT:
Detailed post on a unit smoked by one of these non-standard USB battery packs:

https://www.snipershide.com/shooting/threads/labradar-battery-issues.7014287/