Firearm Magazine with Round Counter

The present Application for Patent is the United States National Phase of International PCT Patent Application No. PCT/US2023/010368, filed Jan. 8, 2023, entitled “FIREARM MAGAZINE WITH ROUND COUNTER” which claims priority to and the benefit of U.S. Provisional Application No. 63/298,322, filed Jan. 11, 2022, entitled “Firearm Magazine with Round Counter,” both aforementioned applications are assigned to the assignee hereof and are hereby expressly incorporated by reference herein.

The present disclosure relates generally to a firearm magazine. In particular, but not by way of limitation, the present disclosure relates to a firearm magazine having a round counting system.

U.S. Pat. No. 9,612,068 discloses a magnet (180) that can be coupled to the spring supporting a magazine follower along with a signaling element (145) coupled to the magazine or another portion of the firearm and configured to detect a proximity of the magnet (180). For instance, the signaling element (145) can include a reed switch or Hall effect sensor. The proximity of the magnet (180) is converted by the signaling element (145) to a signal indicative of the ammunition status of the firearm (105). The signaling element (145) can then send a wired or wireless signal to a reporting element (130, 135) to display a remaining round count to the firearm user. There are no sensors within the magazine.

U.S. Pat. No. 9,784,511 discloses a magnet (33) on the follower (38) or compression spring (34) that causes physical displacement of tactile indicators (44) on an outside of the magazine to thereby provide a tactile indication of the follower position within the magazine.

U.S. Pat. No. 8,215,044 discloses a gray encoded ferromagnetic strip arranged along the magazine to indicate a location of the follower and thus round count of a magazine.

Great Britain application No. WO2018172738 discloses a round-counting device for monitoring the number of ammunition rounds contained in a firearm magazine. The system includes a magnet mounted to the follower and a plurality of reed switches arranged in a spaced apart arrangement along a length of the magazine. When the follower is in a given position, adjacent reed switches are activated, and provide a signal indicative of the number of rounds in the magazine.

U.S. Pat. No. 5,303,495 discloses a handgun with a grip that fully-encloses a magazine. The firearm also includes a permanent magnet (92) mounted on a top rung of a magazine spring 93 and a series of Hall effect switches (94) that are surface mounted on a mylar substrate (95) in the hollow handle of the firearm. The number of Hall effect switches (94) is equal to the number of cartridges to be counted and the switches (94) are positioned one cartridge diameter apart at positions where the magnet (92) will be located directly adjacent to a switch 94 as each round is fired. Only one Hall effect switch (94) at a time is activated. There are no sensors in the magazine.

United States Publication No. 2011/0252682 discloses receptor means (41) (e.g., Hall effect sensors) in a pistol grip or magazine well of a long firearm that sense a magnetic field strength of a magnet (24) positioned on a cartridge lifter (22). In the case of the long firearm, this disclosure suggests that there is only a need to monitor the last cartridges in the magazine (21), and therefore receptor means (41) are only placed in an area adjacent to the upper part of the magazine (21) (i.e., only in the magazine well). There are no sensors in the magazine.

The following presents a simplified summary relating to one or more aspects and/or embodiments disclosed herein. As such, the following summary should not be considered an extensive overview relating to all contemplated aspects and/or embodiments, nor should the following summary be regarded to identify key or critical elements relating to all contemplated aspects and/or embodiments or to delineate the scope associated with any particular aspect and/or embodiment. Accordingly, the following summary has the sole purpose to present certain concepts relating to one or more aspects and/or embodiments relating to the mechanisms disclosed herein in a simplified form to precede the detailed description presented below.

In some aspects, the techniques described herein relate to a magazine for a firearm, including: a housing, the housing having a proximal end and a distal end; a follower having at least one magnet; a plurality of indentations formed in a first channel on a first side of the housing, wherein each indentation of the plurality of indentations includes a magnetic sensor, and wherein the first channel is positioned adjacent a path of the at least one magnet when the follower moves along a length of the housing; at least one side cover positioned on at least one side of the housing, including at least a first side cover positioned on the first side of the housing, and wherein the plurality of indentations including the magnetic sensors are positioned between the first side cover and a bottom of the first channel; a floor plate assembly positioned at the distal end of the housing, wherein the floor plate assembly includes: a floor plate, wherein at least a portion of the floor plate is positioned below an opening in the distal end of the housing, and wherein the floor plate includes a receptacle; and a lock plate, and wherein the receptacle is shaped and sized to receive at least one power source and at least a portion of the lock plate.

In some aspects, the techniques described herein relate to a magazine for a firearm, including: a housing, the housing having a proximal end and a distal end; a follower; a plurality of indentations formed in a first channel on a first side of the housing, wherein each indentation of the plurality of indentations is shaped and sized to receive a magnetic sensor; a first side cover positioned on a first side of the housing, wherein the plurality of indentations including magnetic sensors are positioned between a bottom of the first channel and the first side cover; a second side cover including a proximal end and a distal end, the second side cover positioned on one of a front side or a rear side of the housing, wherein the second side cover includes a second channel extending along at least a portion of a length of the second side cover; a circuit board; a floor plate assembly positioned at the distal end of the housing, wherein the floor plate assembly includes: a floor plate having a horizontal portion and a vertical portion, wherein the vertical portion is positioned at one end of the horizontal portion and extends proximally to the horizontal portion; a lock plate, wherein at least a portion of the lock plate extends through the floor plate; wherein the vertical portion of the floor plate is configured to interface with the distal end of the second side cover; and wherein at least a portion of the circuit board is positioned in a gap between the vertical portion of the floor plate and one of the front or the rear side of the housing.

In some aspects, the techniques described herein relate to a round-counting magazine including: a housing configured to hold a stack of two or more cartridges and having a feed end opposite to a distal end, and a front end opposite to a rear end; an end plate slidingly coupled to the distal end of the housing; a follower slidingly arranged within the magazine and biased to feed the two or more cartridges toward the feed end of the housing; a channel running along a first side of the housing from substantially the feed end of housing to substantially the distal end of the housing, the channel aligned with a path traversed by one or more magnets of the follower; a recess intersecting the channel and running along the first side of the housing between the channel and a rear end of the housing; a plurality of magnetic sensors arranged along the first channel; a first electrical bus arranged in the second channel and configured to inductively draw power from a magazine well of a firearm; a power assembly affixed to the end plate, the power assembly including: a power storage device; and a second electrical bus coupled between the power storage device, the first electrical bus, and the plurality of magnetic sensors.

Some embodiments of the disclosure may be characterized as a round counting system for a firearm with a detachable magazine, the system comprising: a magazine comprising at least a follower, the follower comprising one or more magnets, and the magazine comprising: <N magnetic-field-sensing sensors arranged substantially along a path of the one or more magnets when the follower moves along a length of the magazine, where N is a maximum number of cartridges that can be loaded in the magazine, the sensors generating round count data based on a position of the one or more magnets relative to the <N magnetic-field-sensing sensors; and a first substantially flat antenna on an inside of the magazine arranged at in a region of the magazine that is configured to fit at least partially within a magazine well of the firearm, the wireless antenna configured to wirelessly transmit a round count indication from the magazine to a substantially flat second wireless antenna on the firearm; and the substantially flat second antenna configured to be affixed to an inside of a magazine well of the firearm and having an area that mostly overlaps with an area of the first substantially flat antenna.

Other embodiments of the disclosure may also be characterized as a round counting system for a firearm with a detachable magazine, the system comprising: a magazine comprising a follower, the follower comprising one or more magnets, and the magazine comprising: Hall effect switches or sensors arranged substantially along a path of the one or more magnets, where N is a maximum number of cartridges that can be loaded in the magazine, the Hall effect switches or sensors each generating a high or low signal based on a position of the one or more magnets relative to each of the Hall effect switches or sensors; and a magazine processor coupled to each of the Hall effect switches or sensors and configured to convert the high or low signal from each of the Hall effect switches or sensors into a single round count indication for the magazine; a magazine antenna on an inside of the magazine arranged in a region of the magazine that is configured to fit at least partially within a magazine well of the firearm, the magazine antenna configured to wirelessly transmit the round count indication from the magazine to a magazine well antenna on the firearm; and the magazine well antenna configured to be affixed to an inside of a magazine well of the firearm and having an area, a majority of which, overlaps with an area of the magazine antenna.

Other embodiments of the disclosure can be characterized as a method of manufacturing a magazine with a round counting system, the magazine comprising a follower, wherein the follower comprises one or more magnets, the method comprising arranging <N magnetic-field-sensing sensors substantially along a path of the one or more magnets when the follower moves along a length of the magazine, where N is a maximum number of cartridges that can be loaded in the magazine, the sensors generating round count data based on a position of the one or more magnets relative to the <N magnetic-field-sensing sensors; and arranging a first substantially flat antenna on an inside of the magazine in a region of the magazine that is configured to fit at least partially within a magazine well of the firearm, the first substantially flat antenna configured to wirelessly transmit a round count indication from the magazine to a substantially flat second wireless antenna on the firearm, the round count indication based on the round count data, wherein the first substantially flat antenna is arranged such that an area of the first substantially flat antenna, defined by a height and width, primarily aligns with an area of a second substantially flat antenna coupled to an inside of a magazine well of the firearm.

Other embodiments of the disclosure can be characterized as a method of installing a round counting system on a firearm, the method comprising installing a detachable magazine comprising a follower, the follower comprising one or more magnets, and the magazine comprising: <N magnetic-field-sensing sensors arranged substantially along a path of the one or more magnets when the follower moves along a length of the magazine, where N is a maximum number of cartridges that can be loaded in the magazine, the sensors generating round count data based on a position of the one or more magnets relative to the <N magnetic-field-sensing sensors; and a first substantially flat antenna on an inside of the magazine arranged in a region of the magazine that is configured to fit at least partially within a magazine well of the firearm; and installing a second substantially flat antenna on an inside of a magazine well of the firearm such that an area of the first substantially flat antenna and an area of the second substantially flat antenna are mostly aligned, the first and second substantially flat antennas configured to exchange a round count indication based on the round count data as well as power via a near-field-communication connection.

Other embodiments of the disclosure can be characterized as a non-transitory, tangible computer readable storage medium, encoded with processor readable instructions to perform a method for detecting and displaying a number of cartridges remaining in a firearm magazine, the firearm magazine comprising a follower, and the follower comprising one or more magnets, the method comprising: arranging <N magnetic-field-sensing sensors substantially along a path of the one or more magnets when the follower moves along a length of the firearm magazine, where N is a maximum number of cartridges that can be loaded in the firearm magazine, the sensors generating round count data based on a position of the one or more magnets relative to the <N magnetic-field-sensing sensors; arranging a first substantially flat antenna on an inside of the firearm magazine in a region of the magazine that is configured to fit at least partially within a magazine well of the firearm, the first substantially flat antenna configured to exchange a round count indication based on the round count data as well as power via a near-field communication connection with a second substantially flat antenna coupled to an inside of a magazine well of the firearm, wherein the first substantially flat antenna is arranged such that an area of the first substantially flat antenna, defined by a height and width, primarily aligns with an area of the second substantially flat antenna coupled to the inside of the magazine well of the firearm.

Despite the industry working to solve the round counting problem for decades (this application references early round counting systems dating to as early as 1992), no solution thus far has overcome all the challenges that the inventors identified. For instance, RADETEC (Rade Tecnologias) has developed two primary lines of round counters: one that is part of a pistol grip and uses a magnet on the follower and magnetic field sensors in the pistol grip to estimate distance of the magnet from those sensors and thereby estimate a position of the follower and hence a number of rounds in the magazine; the second is directed to long gun platforms, such as the AR-15, and this system again uses a magnet on the follower, but a magnetic field sensor in the magazine well or receiver to detect a distance between the magnet and the sensors. Both systems rely on analog magnetic field sensors that are prone to low signal to noise ratios and thus erroneous readings. They also both require “long distance” magnetic field sensing. Magnetic field strength drops off exponentially with distance (e.g., r) and thus even small increases in distance have a profound influence on field strength. By locating the magnet inside the magazine, and the sensors outside the magazine, either in the pistol grip or in the receiver, the magnetic field is greatly diminished by the time it reaches the sensors. Additionally, in the case of the long gun version, since sensors are only arranged on the magazine well or receiver, the magnet is even further away for fully-loaded and near-fully-loaded magazines. What is more, layers of material (e.g., metal) between the magnet and the sensors can further interfere with and degrade the magnetic field detected at the sensors, and often the thickness of this material is not consistent along a length of the magazine. For instance, in the long gun version, the magazine well does not extend down the entire length of the magazine, meaning that different materials and thicknesses of material are interposed between the magnet and the sensor(s) for different follower positions. All of these factors lead to a system that suffers from high and varying signal to noise ratios and ultimately to inaccurate round counts. From an ease-of-use standpoint, the Radetec technology also requires the user to calibrate the system before use, and such calibration is undesirable.

The inventors overcame the problems that have faced the industry unresolved for over thirty years via a combination of some or all of the following: (1) use of Hall effect switches rather than Hall effect sensors; (2) arranging Hall effect switches along a full length of the follower path so that there is consistent signal strength and consistently high signal-to-noise for each cartridge position; (3) arranging magnetic sensors within the magazine where they are close to the magnet on the follower thereby maximizing magnetic field strength at the sensors; (4) arranging a flat Near Field Communications (NFC) antenna within the magazine well; (5) arranging a processor within the magazine to process sensor signals before transmission across the wireless connection; and (6) energy harvesting from a power source on the firearm through the NFC connection.

Most systems rely on Hall effect sensors rather than Hall effect switches to detect a magnet in a follower since these more advanced sensors can better determine a position of a magnet when used singularly (e.g., a Hall effect sensor provides an analogue signal proportional to magnetic field strength and hence to distance, whereas a single Hall effect switch provides either a high or low signal as a function of a threshold magnetic field). For the purposes of this disclosure, a “Hall switch” is one providing a digital or at least pulsed or square wave output, as compared to a fluctuating or sinusoidal analogue output. However, Hall effect sensors are susceptible to many of the variables noted above relative to the Radetec platform, and because of these systems using Hall effect sensors often require user calibration. Hall effect sensors may also require an analogue to digital converter (ADC). The inventors unexpectedly found that the simpler Hall effect switch, when used in an array having <N switches (or N/2) (N=maximum number of cartridges in the magazine), avoids the need for an ADC and calibration and can provide more accurate follower position than an array of Hall effect sensors equal to the number of cartridge positions in the magazine.

To implement a Hall effect switch array where the number of switches is <N, a processor may be used to assess the signals from the array and looks for two scenarios: (1) where only a single Hall effect switch is active, the follower is likely closely aligned with that Hall effect switch; and (2) where two Hall effect switches are active, the follower is likely roughly between the two switches. Using these two scenarios, the processor can distinguish between each and every cartridge position, even though <N or N/2 or N/3 or N/4 Hall effect switches are used. Reducing the number of switches also decreases cost and complexity.

Another advantage of using Hall effect switches is that the processor can analyze the switch outputs and determine a number of cartridges without storing any state or other data in memory. Thus, a processor with less or no cache/memory can be implemented. Alternatively, this implementation may allow a processor with cache/memory to use less of the cache/memory for round count processing.

While Hall effect sensors can estimate distance to a moving magnet using a single sensor, such systems can also introduce errors since each cartridge position must be associated with a unique magnetic field strength. By positioning magnetic-field-sensing sensors along a full length of the magazine, the sensors can be arranged such that each cartridge position can be associated with a consistent magnetic field strength, thereby greatly reducing errors. This also helps to avoid the calibration challenges seen in the prior art.

(3) Sensors within the Magazine

Most existing systems use sensors outside of the magazine as this simplifies manufacturing and design. This also avoids the challenge of having to wirelessly convey data from the magazine to the firearm. However, the inventors found that these systems are not accurate enough for practical implementation. Therefore, the inventors chose the more complex route of locating sensors within the magazine. This introduced challenges associated with getting round count data from the magazine to the firearm that have not been addressed in detail in the art. For instance, U.S. Pat. No. 9,612,068 vaguely notes that round count information can be wireless transmitted to a display, but provides no enabling details surrounding this so-called wireless embodiment. WO2018172738 also vaguely suggests that a wireless chip can be implemented, but makes no further discussion regarding details needed to implement this wireless embodiment. By taking on this challenge, the inventors achieve more consistent magnetic field strength measurements since there is little to no material between the follower's magnet and the magnetic-field-strength sensors. Also, by locating the sensors closer to the follower than the prior art, the inventors could pick up on the strongest magnetic field possible, thereby further reducing errors.

(4) Antenna within the Magazine Well

In practice, wireless communication between the magazine and the firearm is fraught with a number of challenges neither recognized nor addressed by known systems. For one, most wireless technologies are power hungry. Power requires batteries, which are heavy, and thus power-hungry wireless systems lead toward heavy firearms-something that is not conducive to in-field usage. While there are known low-power wireless protocols, such as near field communication (NFC), these protocols only operate over very short distances and often have difficulty with signals that pass through anything but air (for instance passing through components of a firearm could lead to errors in data transmission). Also, since a firearm is a high tolerance device and designed to fit into the smallest space available, there is not extraneous space to insert or arrange antennas. However, the inventors discovered that there are two unused areas of a firearm that are in close proximity, such that they don't require any metal components between them, which turned out to be an ideal location for two interoperable flat NFC antennas. Namely, in the forward part of a magazine where the magazine tapers, there is room in a polymer magazine that can be carved out to fit a flat NFC antenna without compromising the magazine's structural integrity. There is also a depression in the left side of an AR-15 magazine well that does not contact the magazine and is just deep enough (e.g., Depth: 0.0175+/−0.0075 inches (0.44+/−0.19 mm), Width: 1.77 inches (45 mm), Height: 2 inches (50.8 mm)) to fit a thin (e.g., thickness: 0.010 inches (0.25 mm), Height: 1.6 inches (40.64 mm), W: 1.050 inches (26.67 mm)) flat NFC antenna without interfering with magazine insertion and removal. In some cases, the NFC antenna may be a microstrip patch antenna fabricated on a dielectric substrate (e.g., ROGERS RT/DUROID or RO3000 or DiClad series composite/laminate, Gallium Arsenide (GaAs), GaN, epoxy, or any other composite or substrate for use in high frequency applications).

Even after the inventors discovered a solution to getting a low power wireless system into the magazine well that avoided metal interference between the antennas, this solution generated a new problem-how to provide wiring access between the antenna inside the magazine well to a display that is on the outside of the receiver. Again, the high tolerances of a firearm do not leave much if any room to run wiring between these two components. Unexpectedly, the substrate of the flat NFC antenna is flexible, and the inventors recognized that a portion of the NFC circuit board could be flexed around a bottom of the magazine well and then stuck to an outside of the magazine well (e.g., see, and) where a connection to an RF cable could be made, in this way avoiding having to drill/machine any openings in the receiver to provide a wiring path for a traditional cable.

(5) Processor within Magazine

Another challenge of placing the sensors within the magazine is minimizing the bandwidth requirements of the wireless connection. The prior art always uses a processor within or on the firearm (e.g., receiver) to process raw data signals from the one or more sensors. If this same technique were applied to the inventor's Hall effect switch approach, then upwards of thirty separate data streams would need to be wirelessly passed through the NFC connection. To avoid this burden on the NFC connection, the inventors found that placing a processor on the magazine to process the Hall effect switch signals allowed a single indication of round count to be passed across the NFC connection, thereby greatly reducing the throughput needs of the NFC connection.

Reducing cost and weight means minimizing the number of batteries needed for the round counting system. Prior art systems may utilize only a single battery, but also benefit from off-magazine systems and thus do not need to provide power to the magazine. Where a magazine does require power, the prior art uses a second on-magazine battery. The inventors have realized a system with a single battery, but also capable of providing power to the magazine. Specifically, the NFC connection can unexpectedly pass both data and power allowing the magazine to upload round count data to the firearm while passing power in the opposite direction, back to the magazine.

As seen, an effective round counting system for firearms with a magazine that is insertable into a magazine well, such as an AR-15 and most semi-automatic long guns, is a complex challenge that requires more than mere design choices. A holistic approach that overcomes a vast set of challenges, was needed. Each inventive discovery often led to a new challenge to be solved, and an inventive balancing of various interests had to be discovered to arrive at a system-level solution. The industry has searched for an effective, reliable, and accurate solution to round counting for over 30 years, with little progress over that time (e.g., U.S. Pat. No. 5,303,495 used a sensor for each cartridge in 1992). Despite this decades-old challenge, no one has yet conceived of a solution as elegant, low power, light weight, accurate, and reliable as the one herein disclosed.

In some cases, reed switches may be a viable alternative to Hall-effect switches. Like Hall-effect switches, reed switches may be examples of electrical switches operated using an applied magnetic field. Reed switches may primarily come in two variants: always on and always off switches. An always on reed switch may disconnect or turn off under the influence of a magnetic field, whereas always off (or closed) reed switches, such as those seen in flip phones or laptops may start flowing current in a magnetic field. In some cases, an always off reed switch may be implemented in a round counting system. For instance, an always off reed switch is activated when a magnet on a follower is adjacent to the reed switch. In such cases, a magnetic processing circuit connected to a plurality of reed switches (e.g., N/2+1) lining the inside of the magazine may identify which of the reed switches has been activated, and from this determine the position of the follower (and the round count). Such an embodiment would enable a lower-power application since reed switches don't need external power.

In some circumstances, capacitive strip encoders may be utilized in a round counting system. Capacitive strip encoders may measure a change in capacitance as a measure of displacement (i.e., linear or rotational) using a high-frequency reference signal. By analyzing the change in capacitance as the follower moves through the magazine, a round count may be determined.

In one example, capacitive sensors, such as those seen in digital calipers, may line the inside of the magazine. In some cases, the follower may comprise a circuit board, and a plurality of rectangular notches (or grates) may be engraved onto a metallic strip inside the magazine. In some cases, the circuit board and the grates on the metallic strip may form a grid of capacitors. Further, as the follower moves along the inside of the magazine, the rectangular notches may align and misalign with the circuit board, causing the capacitance to change. In some cases, a processor within the magazine, or the firearm may determine a position of the follower within the magazine (and a round count) based on analyzing this varying capacitance.

In some circumstances, Radio Frequency Identification (RFID) tags may be utilized in a round counting system. For instance, an RFID tag may be placed on the follower in order to accurately determine its location within the magazine. In some examples, an RFID reader may be placed on the weapon (e.g., on the magazine well, trigger guard, or elsewhere on the receiver), and the follower's location may be determined based on a time delay of signals received from the RFID tag. In some other cases, unique RFID tags may be embedded within each round of the magazine (e.g., attached to or within each cartridge), and the magazine round counting system may determine the number of rounds expended (or remaining) based on the RFID reader scanning the rounds remaining in the magazine. Thus, the RFID reader may also be used to identify an empty state of the magazine, if no RFID tags are identified.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

Preliminary note: the flowcharts and block diagrams in the following Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, some blocks in these flowcharts or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

The following illustrations and detailed descriptions of the various embodiments will help the reader to understand and appreciate the inventive concepts noted above.

is a side view of a firearm receiver and a detachable magazine, illustrating an embodiment of a magnetic sensor-based round counting system. The firearmcan include a magazinehaving a follower, and one or more magnetsattached to the followeror a compression spring. The magazinecan also include an array of magnetic sensors(e.g., Hall effect switches). The arraycan span an entire height of the magazineor some subset thereof. For instance, if the magnet(s)is arranged at a platformof the follower, the follower may have tinesthat prevent the follower platformfrom reaching a bottom of the magazinewhen the magazineis fully loaded. The bottom of the arraycan be roughly aligned with a position of the magnet(s), or roughly the follower platformheight above a bottom of the magazine. The arraycan extend to a top of the magazineor some position below a top of the magazine.

When the one or more magnetsare within a threshold detection range of one or more of the magnetic sensors, those sensorscan generate a detection signal and provide this to a magnetic sensor processing circuitry. The processing circuitry can compare signals from the sensorsto ascertain a position of the followerand convert this position to a number of rounds remaining (or number of rounds expended). The round count can then be passed to transmitter, which wirelessly transmits the round count to a wireless receiverand passes the round count to a display device. As illustrated, the display deviceis a digital display affixed to an exterior of a red dot scope, but this is in no way limiting. For instance the display devicecan be arranged on the firearm (e.g., a digital display integrated within or affixed to an outside of a scope; a digital display coupled to an outside of the firearm receiver, a digital display arranged on a visible portion of the magazine, etc.), but may also be arranged on a user (e.g., in a display of glasses/goggles). The display devicecan be part of a scope or iron sight, but can also be a display separate from a sights/targeting means. Although the transmitterand the receiverare illustrated as being separated by a few inches, in other embodiments, these can be NFC interfaces and each can be arranged within a few millimeters, for instance with the transmitter just under the magazine well, and the receiveron a portion of the trigger guard closest to a bottom of the magazine well. In particular, a small (e.g., 5 mm×5 mm) receiver or transceiver (e.g., TC0502HF from PREMO) can be mounted on or within an end of the horizontal portion of the trigger guard where it meets the magazine well. Electrical communication between this receiver or transceiver and a transmitter or transceiver in the grip could be made through of on the length of the trigger guard (e.g., an electrical trace along a bottom surface of the trigger guard). The transmitter or transceiver in the grip could wirelessly communicate data to a display thereby avoiding wiring or leads snaking along a side of the firearm. Alternatively, wired communication could also be made from the receiver or transceiver on or in the end of the trigger guard to a display device. A processor or reader may be arranged in the grip to analyze raw data from the round counter in the magazine and convert that data to a displayable form for transport to the display or other devices remote from the firearm.

A typical magnetic sensorbegins to detect the one or more magnetsat a distance, and the strength of this detection increases as the one or more magnetsget closer to the sensor. So, for instance, where each sensorgenerates a voltage proportional to the magnetic field generated by the one or more magnets, this voltage will increase as the one or more magnetsapproach the sensor. When the voltage exceeds a threshold, the processing circuitrycan determine that the followeris proximal to the sensorwhose voltage exceeds the threshold.

Each sensorcan include an analogue to digital converterfollowed by a digital comparatorthat compares the digital signal from the digital converterto a reference signalor threshold. Where the digital comparatorfinds that the signal from the digital converterexceeds the reference signal, the detection signal can be generated and passed to the magnetic sensor processing circuitry.

shows a variation where each sensorincludes an analogue to digital converter, a reference signal, and a comparator, where the outputs of the comparatorsare provided to the processing circuitry.illustrates an embodiment where the outputs of each sensorare converted to digital and then passed to the processing circuitry, and where comparatorsof the processing circuitrydetermine whether each signal exceeds the reference signal.

shows a variation where each sensorcan include an analogue comparatorthat compares the analogue output of the sensorto a reference signal. Where the analogue comparatorfinds that the signal from the sensorexceeds the reference signal, the detection signal can be generated and passed to the magnetic sensor processing circuitry.illustrates an embodiment where the outputs of each sensorare passed to the processing circuitry, and where comparatorsof the processing circuitrydetermine whether each signal exceeds the reference signal.

In another embodiment, each sensorcan provide its signal in analogue or digital form (where an analogue to digital converter (ADC) is interspersed between the sensor and the magnetic sensor processing circuitry) to the magnetic sensor processing circuitry. The magnetic sensor processing circuitrycan then process these signals and ascertain a position of the follower. For instance, the magnetic sensor processing circuitrymay be programmed or wired to determine that a sensorhaving the strongest signal is closest to the follower. The magnetic sensor processing circuitrycan be hardwired with data, or include data in memory, providing a position of each sensor.

In some examples, reference signalmay be a threshold with which the output value of the sensoris compared to, prior to being passed to the magnetic sensor processing circuitry. In one embodiment, the threshold value may be slightly lower than an output value of the sensor(s)when the magnet is roughly equidistant from two sensors. For instance, when a magnet is positioned between two adjacent sensors, and the output voltages from the sensors are 2 V and 2.1 V, respectively, the reference signalmay be set as <2 V (e.g., 1.95 V). In such cases, output readings from sensors that are further away may not be passed on to the processing circuitry (i.e., if <1.95 volts). In some embodiments, an operational amplifier (or op-amp) may be used as a voltage comparator. The polarity of an op-amp's output circuit depends on the polarity of the difference between the two input voltages (i.e., input voltage and reference voltage), and thus an op-amp may be used as a voltage comparator.

For instance, comparator(or) may comprise an op-amp, where a first reference voltage (e.g., reference signal) is applied to an inverting input of the op-amp, and the voltage to be compared (i.e., output from sensor's) with the reference voltage is applied to the non-inverting input. In some examples, a resistive voltage divider (i.e., for constant reference), or a battery source, diode, or potentiometer (i.e., for variable reference) may be used to set the input reference voltage (i.e., reference signalor) for the comparator.

The output voltage of the op-amp may depend on the value of the input voltage relative to the reference voltage. For instance, if the input voltage is less than the reference voltage, the output voltage is negative; if equal to reference voltage, output voltage is zero; if greater than reference voltage, output voltage is positive. Thus, only signals exceeding the reference signal(or) may be filtered and passed on to circuitryfor further processing, based on the polarity and/or magnitude of the output voltage from the comparator or op-amp.

The arraycan include one sensor for each cartridge, where each sensoris roughly arranged at a position where a cartridge will stop. However, in other embodiments, there may be one sensorfor every two cartridges: when a sensorgenerates a strong signal and the two adjacent sensorsgenerate much weaker signals, then the magnetic sensor processing circuitrymay determine that the magnet(s)is closest to the sensorproviding the strong signal; and when two adjacent sensorsprovide roughly the same signal, then the magnetic sensor processing circuitrymay determine that the magnet(s)is between those two sensors. This arrangement could decrease the number of sensorsand thus the complexity and cost of the array.