What a Light Gun Needs — Every Input, by Game, Genre and Platform

1.1 What This Dive Owns

The light gun in this category is being built as a working instrument, so every control on it has three lives: a human-interface life (what the player needs and where a finger finds it), a mechanical life (what switch, what force, what travel, how long it lasts) and an electrical and firmware life (which pin, which pull-up, what the firmware reports to the computer). This dive owns the first two. The third is owned elsewhere, and this dive links to it rather than repeating it:

• The wiring of every input — the pull-ups, the optional RC filter, the Hall-effect trigger circuit, the connectors and the pin budget — is in Reference Electronics, Volume 4 and Volume 2.
• What each button sends to the computer — the on-screen, off-screen and gamepad assignments in the OpenFIRE App, the off-screen reload modes, Low Buttons Mode — is in Open-Source Firmware, Volume 6 and Volume 5.
• Repairing the switches in classic guns is in Modding Classic Light Guns, Volume 2.
• Reloading by shooting off the screen, and why the edge needs hysteresis, is in Aiming Maths and Calibration, Volume 7.
• A motion sensor as an input (point-down reloads, a flick for a pump) is in Positional and Inertial, Volume 6; the owner has decided to fit one to the first carrier (decision D36).

The volumes of this dive run in the order a designer meets the questions: what inputs a gun needs (this volume), where they go on an MP7 (Volume 2), what switches to build them from (Volume 3), how the trigger should feel (Volume 4), how bounce and timing are handled (Volume 5), pumps and pedals (Volume 6), and feedback, accessibility and the final input map (Volume 7).

1.2 The Arcade Minimum: a Trigger and a Way to Reload

The arcade games that defined the genre were designed for a cabinet with a gun, a start button and sometimes a pedal. That is worth stating first, because it means the large majority of the light-gun library needs two inputs: something to fire and something to reload.

Namco’s operator manuals for its Time Crisis cabinets describe the whole player interface in three lines. From the Time Crisis II manual (section 7-2-1, “How to control”):

1. Step on the pedal = attack position: At this position, you can shoot the enemy. You are also subject to an enemy attack.
2. Release the pedal = defence position: At this position, you are hidden behind an object. You are not subject to an enemy attack. Releasing the pedal recharges the gun.

The Time Crisis 4 deluxe cabinet manual uses the same two states and then loads further functions onto them rather than adding buttons. Weapon selection is “releasing the pedal and pressing the trigger”; in a sniper event, “When the pedal is pressed, the screen zooms toward the target. When the pedal is released, the ammunition will be reloaded”; the special machine gun “shoots continuously, while the trigger is pressed”. A four-weapon game with zoom and cover, played with one trigger and one foot switch, is the clearest evidence that the arcade designers treated every extra control as a cost.

Games without a pedal reload with the gun itself. The common convention is the off-screen shot: point the gun away from the picture and pull the trigger. It needs no extra hardware at all, which is why the original GunCon could ship with two side buttons that, in Wikipedia’s description, both performed the same function. On a camera gun the off-screen shot is a computed state, not a sensor reading, and it has a known weakness at the edge of the screen (Aiming Maths and Calibration, Volume 7, §7.8). A dedicated reload button removes the geometry from the problem, which is the argument for one in Volume 2.

1.3 Every Input, One by One

OpenFIRE, the firmware the build runs (Open-Source Firmware), knows fourteen button functions, three hardware toggles and two analog axes (boardInputs_Strings in OpenFIREshared.h, read in Reference Electronics, Volume 4, §4.2). Taking them in the order a player meets them:

Table 1 — OpenFIRE, the firmware the build runs ([Open-Source Firmware](/light-guns/building-the-electronics/open-source-firmware/)), knows fourteen button functions, three hardware toggles and two analog axes (boardInputsStrings in OpenFIREshared.h, read in [Reference Electronics, Volume 4, §4.2](/light-guns/building-the-electronics/reference-electronics/vol-4/)). Taking them in the order a player meets them

Input	What it is for	Who needs it	Firmware name
Trigger	Fire. Also the “OK” of every calibration step and many menus	Every game	Trigger
Reload	Reload without leaving the screen	Games that reload off-screen (any gun can), console games that read a button, players who want the edge problem gone	none; usually Button C or a pedal
A, B	Secondary actions: grenade, weapon change, special	PC titles and console games; a few arcade ports	Button A, Button B
C	A third action; on GunCon 2 it sits at the bottom of the grip	Console games written for the GunCon 2	Button C
Start, Select	Start a game, insert a credit, pause	Every emulated arcade game (the cabinet had them), every console game	Start, Select
D-pad	Menus, map screens, cursor nudging	Console games, front-ends, the firmware’s own pause menu	D-Pad Up/Down/Left/Right
Home	Enter the firmware’s pause and calibration menu	The gun itself, not games	Home Button
Pump	A shotgun slide: reload, or cock	Shotgun games; Sinden users map reload to it	Pump Action
Pedal	Cover (Time Crisis), or reload	Cover shooters; any game as a reload	Pedal
Alt pedal	A second foot function	A few titles; rare	Alt Pedal
Rumble, solenoid, autofire switches	Hardware toggles that override the pause menu	A gun handed to other people	Rumble/Solenoid/Autofire Switch
Analog stick X and Y	A thumbstick	GunCon 3 games	Analog Stick X/Y

Three points from the table shape everything that follows.

The firmware has no “reload” function. A reload is whatever the game decides it is: an off-screen trigger, a mouse button, a key. OpenFIRE’s defaults send Button C as mouse button 4 and the pedal as mouse button 4 too (Open-Source Firmware, Volume 6, §6.3), so in mouse mode a magazine-release switch wired as Button C and a foot pedal arrive at the game as the same button. That is a useful default: one game binding covers both.

Start and Select are not optional on an emulated arcade game. The cabinet had start buttons and a coin slot. On an emulator they are keys, and OpenFIRE sends them as player-relative keys (1 and 5 for player 1). A gun without them forces the player back to the keyboard between every credit.

Home is for the gun, not the game. It enters OpenFIRE’s pause mode, where calibration, profiles and the toggles live (Open-Source Firmware, Volume 5). It should be reachable but hard to press by accident, a point Volume 2 returns to.

1.4 By Genre

Table 2 — 1.4 By Genre

Genre	Typical titles	Inputs used	Notes
Rail shooter, off-screen reload	Virtua Cop, The House of the Dead series	Trigger; reload by off-screen shot	The whole game on one switch. A reload button is a convenience
Cover shooter	Time Crisis series	Trigger, pedal	Pedal held = out of cover; released = hide and reload (Namco manuals). Without a pedal, a button stands in (1.5)
Party and gallery	Point Blank	Trigger, start	Namco’s Point Blank operator’s manual names only the gun trigger and the 1- and 2-player start buttons
Shotgun games	hunting and shotgun titles	Trigger, pump	A pump is the realistic reload; any reload button works
Console games written for the GunCon 2	PS2 titles	Trigger, A, B, C, Start, Select, D-pad	The D-pad and C exist because these games had menus and extra actions
GunCon 3 games	PS3 titles	Trigger, two sticks, six buttons	The only common use for analog sticks on a gun
Modern PC light-gun games	e.g. Railbreak	Trigger, reload, two or more side buttons	A Steam discussion of Railbreak with the Sinden maps front-left (or pump) to reload, rear-left to grenade, front-right to weapon switch
Emulator front-ends and the gun’s own menus	RetroArch, MAME, OpenFIRE pause mode	D-pad, Start, Select, Home, trigger	The reason a D-pad earns its place on a gun with a mouse cursor

Virtua Cop 3 is the edge case the firmware’s own release notes single out: OpenFIRE v5.2 added off-screen and low-button modes for it, “with a single button gun + pedal” (Open-Source Firmware, Volume 6).

1.5 By Platform

Arcade cabinets. Gun, cabinet start buttons, pedal where the game had one. The guns themselves were simple: Namco’s parts list for the Time Crisis SD cabinet gives the gun’s switch as one microswitch, an Omron SS-01GL2T (Volume 3 explains why that part matters), and the pedal as a plunger pressing a second microswitch.

PlayStation. Wikipedia’s account of the GunCon family gives the progression. The original GunCon had “buttons A and B, both performing the same function”, below the barrel on either side. When Time Crisis came home without a pedal, a button command replaced it; Wikipedia reports reviewers split between a joypad button under the foot and the GunCon’s own button, GameSpot preferring the latter “because it encourages a two-handed grip”. The GunCon 2 moved A and B rearward “to a position directly above the trigger”, added “two new smaller buttons, SELECT and START” on the left side, a D-pad at the back of the barrel and a C button at the bottom of the handle. The GunCon 3 added “an analog stick and two shoulder buttons” on a sub-grip under the barrel, a second stick at the rear with buttons B1 and B2, and C1 and C2 on the left of the barrel.

The Sinden Lightgun, the commercial border-tracking gun, has, in Time Extension’s review, “four buttons – two on either side of the barrel – as well as a D-pad”, and a “pump-action bar on the base of the gun”; reload in Time Crisis can be “the button on the side or the aforementioned pump-action bar”. Sinden sells a separate USB pedal (Volume 6).

The open firmware. OpenFIRE’s default Pico map gives every one of its fourteen button functions a pin except Alt Pedal (Open-Source Firmware, Volume 3, §3.10). Its defaults are a close copy of the GunCon 2’s set plus a pump and a pedal. That is the right reading of it: a gun built to that list can play everything above except the GunCon 3’s stick games.

1.6 The Input Set for This Build

The first gun is a 3D-printed MP7 (decision D35, 2026-10-19), built on a Pico with a Hall-effect trigger (D2, D8). The set below is what this dive proposes for it. Volume 2 places each one on the gun, Volume 3 chooses each switch and Volume 7 assembles the final map.

Table 3 — 1.6 The Input Set for This Build

#	Input	On the MP7	Firmware function	Required for
1	Trigger	the trigger, Hall-effect	Trigger	everything
2	Reload	the magazine catch	Button C	console and PC games; the edge problem
3	A	left thumb, above the grip	Button A	secondary actions
4	B	right side, above the grip (index finger, left-handed: thumb)	Button B	secondary actions
5–8	D-pad	left side of the receiver, thumb reach	D-Pad	menus
9	Home	centre press of the same five-way switch	Home Button	the firmware’s own menu
10, 11	Start, Select	rear of the receiver, both hands off the grip	Start, Select	every emulated arcade game
12	Pump	the folding fore-grip, pulled back	Pump Action	shotgun games; a second reload
13	Pedal	a 3.5 mm jack on the gun’s cable, to a floor pedal	Pedal	cover shooters
14	Alt pedal	unassigned	Alt Pedal
T1	Autofire	the fire selector at its “burst” position	Autofire Switch	a held trigger fires continuously
T2	Recoil off	the fire selector at its “safe” position	Solenoid Switch	quiet play; handing the gun over

Counted against the pin budget (Reference Electronics, Volume 2, §2.5), that is the analog trigger plus fourteen digital inputs: the thirteen the budget already carries (A, B, C, four D-pad, Start, Select, Home, Pump, Pedal and the Solenoid Switch) and one more, the Autofire Switch. The stopgap build’s one spare pin, GP15, takes it. The kit-camera build has 26 functions on 26 pins and no spare, so on that board autofire stays a pause-menu setting and the selector’s “burst” position does nothing until a pin is found. Alt Pedal is left unwired on both. Volume 7 counts it again against the final carrier.

1.7 Why This, and Why Not the Others

Table 4 — 1.7 Why This, and Why Not the Others

Option	Verdict	Reason
Trigger + off-screen reload only (arcade minimum)	Rejected as the whole set	Plays the arcade library, but not console games, front-ends or the firmware’s menus, and leaves the edge problem in every reload
The OpenFIRE default set (GunCon 2 + pump + pedal)	Adopted, with Alt Pedal unwired	Covers every genre in 1.4 except GunCon 3 stick games; every function already exists in stock firmware
Analog sticks (GunCon 3)	Rejected for the first gun	Two ADC pins; the Pico has one spare analog input after the Hall trigger and TMP36, and the kit-camera budget has none (Reference Electronics, Volume 2). Only GunCon 3 games use them
More side buttons (Sinden’s four)	Rejected	No firmware function to send them as beyond A, B and C, and no pin for them
A second pedal on the same gun	Deferred	Alt Pedal exists in firmware; it is the cheapest addition if a game needs it, since a pedal is a jack and one pin
An IMU as a reload gesture	Complement, not substitute	The owner chose an IMU on the carrier (D36). A point-down reload works with the camera blind (Positional and Inertial, Volume 6), but it is firmware work in the fork and cannot replace a button on day one

1.8 What Could Not Be Verified

• The Sinden button list comes from a review and a Steam discussion, not from Sinden’s own documentation; Sinden’s site pages read on 2026-10-19 did not describe the controls.
• Sinden’s reference image in the owner’s file has no recorded source.
• The Railbreak mapping is one user’s configuration, quoted as an example of how side buttons get used, not as the game’s default.
• No game-by-game survey of input use across the whole light-gun library exists; 1.4 is built from the manuals and sources named.

Sources

1. Namco, Time Crisis II Operation Manual (arcade), §7-2-1 “How to control” and §8 maintenance. Central Library, namco-time-crisis-ii-operation-manual-arcade (read 2026-10-19).
2. Namco, Time Crisis 4 DX Operators Manual, Issue 2 (part no. 90500167), “How to Play”. Central Library, namco-time-crisis-4-dx-manual-issue-2-arcade (read 2026-10-19).
3. Namco, Time Crisis SD Operation Manual, §9-4 Pedal Assy and §9-5 Gun Assy parts lists. Central Library, namco-time-crisis-sd-operation-manual-arcade-gun-solenoid (read 2026-10-19).
4. Namco, Point Blank Operators Manual (part no. 90500078), test-mode and setup sections. Central Library, namco-point-blank-operators-manual-90500078-arcade (read 2026-10-19).
5. Wikipedia, “GunCon”, https://en.wikipedia.org/wiki/GunCon (read 2026-10-19).
6. Wikipedia, “Time Crisis (video game)”, https://en.wikipedia.org/wiki/Time_Crisis_(video_game) (read 2026-10-19).
7. Time Extension, “Sinden Light Gun” review, https://www.timeextension.com/reviews/sinden-light-gun-old-school-arcade-blasting-on-your-modern-day-tv (read 2026-10-19).
8. Steam Community discussion of Railbreak with the Sinden Lightgun, https://steamcommunity.com/app/2587170/discussions/0/4031348734037664585 (search result, 2026-10-19).
9. TeamOpenFIRE, OpenFIRE-Firmware v6.2, OpenFIREmain/OpenFIREprefs.h (button descriptor table), and OpenFIRE-Boards OpenFIREshared.h (read 2026-10-19).