Laser for Dry Fire Practice

Winter boredom. Too cold to go to the rifle range. A friend of mine was demonstrating a laser training rig for indoor practice using his target rifle. I said to myself, I can make one of these, in fact I think I have enough parts floating around my basement. One day later I was having fun at home with two of my my high powered rifles shooting laser beams at a free target shooting app called LaserHit.

Note, that there are laser training cartridges available commercially, but the selection of rifle calibers are limited and they seem to be out of stock everywhere. In addition, the commercial laser cartridge fits in the rifle chamber and where it points, it points- you can't really line up the laser dot with the rifle scope/sights without adjusting the sights if the software doesn't have an offset capability. In addition, you require a different laser cartridge for each rifle you want to use. This "basement" version can be moved from rifle to rifle and can be adjusted to have the laser point where required.

The guts of this instructable is a $1.75 laser pet toy from the Dollar Store, a $10 Arduino Uno knock off, and a piezo sensor salvaged from an old fire alarm beeper.

I am linking to online suppliers of parts as examples, but most of these items can be sourced locally or scavenged from items around the house.

Laser Pointer- I used one from the local Dollar Store

Arduino Uno- or clone

Piezo sensor (can be removed from old alarm or beeper)

1 meg ohm resistor (any value from 100K to 1 Meg will do). Try to salvage one from an old piece

of electronics or just purchase an assortment as resistors are handy to have around.

Round magnet to fit Piezo.

Large magnet to attach to rifle barrel

1 1/2 inch angle bracket

1 inch #8- 32 machine screw, nuts, washer, lock washer Qty 2

1 1/2 inch hose clamp (sized to fit rifle barrel)

6 foot cable to connect Arduino to laser and piezo sensor (I used RCA cables and connectors that I had around)

female connectors to accept cable above (fit these to piezo, laser and arduino)

Misc:

2 inches of 1/2 inch rigid plastic pipe

2 inches 3/4 to 1 inch rigid plastic pipe (to fit barrel)

box to house arduino,

1 foot electrical tape

2 inches of duct tape

2 inches of 2 way carpet tape

some rosin core solder and soldering iron

4 x one foot pieces of 22 ish gage wire of various colors (this can be stripped from a piece of computer network cable).

4 inches of 1/2 inch wide by 1/4 inch thick closed cell foam or weather stripping.

Hot melt glue

5 volt cell phone charger or 9 volt battery with barrel connector (5.5 mm OD, 2.1 mm ID)

USB type A to Type B cable to connect cell phone charger to Arduino (same as used for USB printer)

1. Unscrew the ends of the laser pointer removing the dome (put the dome aside for later), key chain holder, and batteries. With a pair of tweezers, reach in to the battery compartment and remove the insulating liner and foam washer.
2. Remove the laser diode and circuit board assembly. This is glued into the metal tube of the pointer. I did this by cutting the rear of the tube with tin snips and peeling back the "petals" of the tube up to the push button switch which can then be removed. Then the rest of the tube body can be carefully cut with a hack saw and peeled open with needle nose pliers. The diode assembly can then be removed. Alternatively, the pointer body can be heated for about 30 seconds with a heat gun or hair dryer. The whole assembly can then be pushed out the front while holding the tube with pliers and using a dowel for a push rod. You do risk melting some of the internal components with this method.
3. The laser diode assembly consists of a laser diode in a barrel housing, complete with a focusing lens, current limiting resistor of 120 ohms and a momentary switch. The anode (positive side) of the laser diode is actually connected to the case of the housing. The cathode (negative side) of the laser diode is connected to one side of the 120 ohm resistor. The other side of the resistor feeds the momentary switch with is not required. Looking at the under side of the switch you will see that there are 4 pins extending through the circuit board. Two are soldered and two are just bent over. Unsolder the two pins (or snip them) and remove the switch.
4. Solder a red wire to the anode of the laser diode as shown in the picture. Looking closely you can see a bit of circuit board raised above the 120 ohm resistor. This is the connection to the anode.
5. Solder a black wire to the side of the 120 ohm resistor that previously connected to the first pin of the momentary switch. The red and black wires will be fed back to the Arduino controller.
6. Finally snip off the remaining bit of circuit board that previously held the other pins of the momentary switch. This will allow a bit more room in the plastic pipe that will hold the laser.

1. Take of the 1.5 inch angle brackets and saw off one half of one side of the bracket as shown in the picture.
2. Take a 2 inch length of 1/2 inch plastic pipe and drill a 3/16 inch hole through the center of the pipe 1 inch from either end to accommodate an #8 machine screw. Place a bit of duct tape over this hole (both side of the pipe) to supply a bit of friction when rotating/adjusting the laser.
3. Screw the dome back on to the laser diode housing and insert the assembly into the pipe, pulling the wires out the back end.
4. Pass the machine screw with flat washer through the pipe, being careful not to pinch the wires. If you didn't snip off the end of the circuit board, it may be interfering with the path of the screw.
5. Attach pass the exiting end of the machine screw through the hole in the long section of the bracket and tighten with lock washer and nut.
6. Take 2 inches of the larger sized plastic pipe and cut it half lengthwise with a hack saw. These two halves of the pipe will bracket the rifle barrel. In one side drill a 3/16 inch hole one inch from the end to accommodate a machine screw. Pass the machine screw through the hole (head against the rifle barrel) and through the hole in the short end of the angle bracket holding the laser. secure with lock washer and nut.
7. Line the inside of the cut pipes with foam or weather stripping so the screw head does not mar the rifle barrel.
8. Attach the assembly to the rifle barrel with the hose clamp.

I used a 27 mm piezo sensor, as that is what I had lying around the basement. A different size is perfectly suitable, if that is what you have available. These sensors can also be used as "beepers" and be found in electronic buzzers, smoke detectors, etc. and can be scavenged from old units.

The sensor requires a resistor of between 1M Ohm and 100K Ohm across the leads. It can be soldered right at the sensor, or as I did, soldered at the input to the controller at the enclosure, whatever is easiest in your particular set up.

Carefully solder the short leads of the sensor to wires long enough to facilitate connectors to a cable to link to your controller box. I used female RCA phono connectors.

I attached the brass side of the sensor to a round magnet with two way carpet tape, and also covered the "white" side of the sensor with some closed cell foam to try to isolate from outside noise and also protect the wires. I used some more two tape to attach the foam. I also wrapped the whole assembly with electrical tape.

I used a second larger and stronger magnet to attach the sensor to the barrel of the rifle. This made a stronger connection then with just the small magnet on the sensor, and also allowed more flexibility in positioning the sensor.

Program the Arduino Uno with the Laser Indicator Software if this has not been completed.

First off- read through the following links to understand the background of the Arduino Microcontroller. You will need to use a computer to load the software on to the Arduino controller. This can be done by using the online tool described in the guide, or installing software directly to your computer. The Arduino is programmed via the USB port on your computer.

Arduino Background:

https://www.arduino.cc/en/Guide

Installing Desktop software:

https://www.arduino.cc/en/Guide/Windows

https://www.arduino.cc/en/Guide/Environment

How to program the Arduino Uno controller:

https://docs.arduino.cc/hardware/uno-rev3

Program the Arduino Uno with this code:

LaserTargetControl.ino

Once the Arduino is programmed, it can be mounted in an enclosure of some type. I used an old plastic box from some nails, but anything non-conductive can be used. I used a small piece of wood to screw the Arduino to, and in turn screwed this to the box.

Rather than soldering to the Arduino, I just tinned the wire connections with solder and inserted the wires into the appropriate pin headers.

There are basically 4 connections to be made (see schematic):

1) A0 on the Arduino to the positive side (red wire) of the Piezo senor

2) D2 on the Arduino to the positive side (red wire) of the Laser Diode.

3) D7 on the Arduino to the open side of the laser test switch (jumper). When this input is connected to ground, the laser will be on continuously.

4) Gnd (Ground) on Arduino to the negative side of the Piezo sensor, Laser Diode and Laser Test switch (jumper).

Finally, the Arduino can be powered either by a 9 volt battery via the barrel connector, or a 5 volt USB (cell phone) charger using a usb type A to B (printer) cable. Preference is to the cell phone charger as the 9 volt battery is depleted quite quickly when the laser is being used in test mode with the laser running continuously.

I used RCA female connections on the box to link to the Piezo and Laser on the rifle via RCA phono cables, however any type of connections can be used.

Also, rather than an actual switch for test mode, I used a shorted RCA male plug that was inserted in the test connector when I wanted to test the laser.

First off, think safety. Make sure there are no live rounds anywhere, and that your rifle is empty.

If using a rimfire rifle make sure to use a "snap cap" or alternative like a drywall anchor in order to prevent damage to your firing pin.

If using a centerfire rifle, normally dry firing is not a problem, but check your rifle manual to ensure that no damage to your firing pin will occur. Snap caps are available for most rifle calibers.

Also remember not to look into the laser as it could cause eye damage.

Attach the laser to the rifle barrel and the large magnet to the barrel near the receiver. Attach the piezo to the large magnet. Connect the laser and piezo to the Arduino box.

Apply the power to the Arduino either by cell phone charger or battery.

Find a suitable location for your target. I am using a 3-9 x rifle scope, and I need at least 30 feet to be able to focus at three power. Higher power scopes should have a parallax adjustment to reduce this distance somewhat.

Mount the rifle in a stable platform and align the scope cross hairs with the center of the target.

Connect the "test" jumper to the Arduino box which should turn on the laser continuously. Now align the laser beam with the scope crosshairs and target center by moving the the laser on the screw pivot points on the mounting bracket. This is the hardest part of the whole procedure as the adjustment is quite delicate and will consist of a few minutes looking through the scope, making an adjustment to the bracket and checking through the scope. I find it is best to keep the screws as tight as possible, only allowing movement of the laser with a bit of effort.

Now remove the test jumper from the Arduino box and the laser should be off.

Sight through the scope at the target and close the bolt. You will probably see some pulses of laser light as you cycle the bolt as the piezo will pick up the vibrations. Press the trigger to fire the action. You should see the 50 msec pulse of laser light on firing.

Now load the LaserHit app onto your Android or Apple Device. I prefer to use an IPAD as the screen is larger and the Apple version of the app allows an offset to be used in case the laser is not striking exactly where the crosshairs on the scope align on target.

Basically, the Laserhit app uses the IPAD/Phone camera to monitor the target area. When the app via the camera "sees" the laser pulse, an image of a bullet hole is overlayed on the target displayed on the IPAD/Phone screen and the sound of a shot is generated. You can select the size of bullet hole, the number of shots per session and a few other options. You must also adjust the target area that will detect the laser pulse as a "shot" and the reset area that allows you to clear the target for a new session. You can also save your "shot targets" as a picture after the session.

I have a rather low end Android phone running Android 7 that does work with LaserHit. I find with this low end phone, a target using an off-white background (inside of a cereal box) seems to work best. Also there is the occasional shot that goes undetected likely due to the low frame rate/quality of the built in camera. I do not have these issues with the IPAD. I found that casting the screen on the Android phone to a big screen TV with Chromecast works great for observing target hits.

Use the "generic" cartridge, red laser, and the "free target program" options. Follow the instructions and have fun. Note, that when cycling the bolt to cock the action, point the rifle away from the target area as the vibrations will trigger the laser and false hits will be registered.

The LaserHit app has many options, but the "free target" program suits my needs. Other upgrades are available at reasonable pricing. There are many videos on the LaserHit site that show the various options and how to use the program.

The video below shows my use of the LaserHit app with my setup.