Wiring the V3b/4 Micro Pulse Rifle Counter

Wiring the V3 Micro Pulse Rifle Counter couldn't be simpler. That's how we designed it. We know that most users of this counter aren't electronic engineers and often don't have much experience with soldering, so it's been designed to be as plug-and-play as possible.

To get yourself up and running all you will need is:

  • The pulse rifle counter
  • The cable connectors supplied with the counter
  • At least two buttons
  • A battery (see below)
  • A switch
  • Some wire
  • Insulation tape, solder and soldering iron (or other means of connecting wires together)

All the important connections to the counter are made through the 5 plugs on the lower edge of the unit. No soldering is required to wire up the unit itself. When viewed from the display side of the board, from left to right, the connectors have the following usage:

  • Power input (This one is slightly separated from the others for better identification)
  • Auxiliary control (see below) - optional (Non-sound) / Speaker output (Sound)
  • Mode select (Auto-fire / Single-shot) - optional (Non-sound) / Auxiliary LED Output (Sound)
  • Magazine detect
  • Trigger

We'll start from the bottom of that list and work up.

Connecting a trigger button

Connecting any buttons to this unit is as simple as plugging in one of the cables into the socket and wiring a normally-open (push-to-make, momentary action) button across the two wires. That's all there is to it. We can't, though, tell you what buttons to use. That very much depends on the specifics of your build. For the trigger you need a button that the trigger itself can press against to activate. That could either be external to your casing (or protruding through it) so that it is within the trigger guard area (between the trigger and the body), or inside the casing where the trigger pivot point or other part of the trigger may be involved. It's up to you to decide on the best solution for your build. A popular choice for the trigger is one of the many forms of microswitch. You can get some pretty small ones, and ones with a flexible lever on them can be good to give plenty of tolerance to the motion of the trigger (as shown to the right).

Simply connect the "COM" and "NO" pins of the button (if they are so labelled - they are the "common" and "normally open" pins) to the two wires of the connector and plug it in. Obviously you will want to extend those wires to the length you need - possibly by soldering them to other wires and wrapping the joints in electrical tape.

Connecting a magazine detect button

The wiring for the magazine button is identical to the trigger button. The operation of this button is slightly different, however. The button should be sited in such a position that while the magazine is inserted the button is constantly being pressed. The same microswitch type shown above could be a good choice. Another good choice, if you have a plastic magazine and shrouds, is to use a reed switch. This is a small glass tube with metal leaves in it which are connected together when in the presence of a magnet. Attach a small (but fairly powerful) magnet to the end of your magazine, with the reed switch placed in the body above it, and when the magazine is inserted the magnet closes the connection. This is ideal if your magazine could be pushed out by the springiness of a button.

The Auxiliary Output EX

This output provides a 50% duty cycle 3.3V pulse while firing. The frequency is the same as the ammo count (one pulse per round). It is intended to interface with our LED driver board, but anything that expects a logic level input can receive this signal. Red wire is the signal, black wire is Ground.

The Speaker Output SP (Sound-variant only)

Connect this directly to a suitable speaker. The default amplifier is 8W, so something around that region is good. It doesn't matter which wire connects to which terminal of the speaker.

Connecting power

The power input connects to your battery via a power switch of your choice. It's important to get the wires connected the right way for this: red to the + and black to the - of the battery.

Non-sound variant power

Because of the brightness of the LEDs the unit is quite power hungry. You should choose a battery with a low voltage (between 3 and 6 volts ideally) and a high capacity. Lithium-ion and similar batteries are the best choice since they give the right voltage range and have plenty of power - and are rechargeable as well. While the unit will accept an input voltage of up to 15V maximum it's not recommended to go above about 6V. This is because all that extra voltage has to be discarded as heat. That's not good, not only from an "it gets hot" perspective, but also it's a real waste of power. However, if your build already has higher voltage batteries in it (for instance an AirSoft conversion) you can still use that higher voltage power source - you just need to "condition" it first.

The most efficient method is to convert the higher (typically 11.4V) output from the batteries into a lower voltage (5V) using an efficient "UBEC" (Universal Battery Elimination Circuit). These are sold by many model aircraft and drone marketplaces and cost very little. Look for one that gives 5V output from an input range that your batteries fit comfortably within (which covers most UBECs on the market). A UBEC works by effectively converting voltage into current. A high voltage, low current input gets converted into a low voltage high current output. This is far more efficient that just dropping the voltage and will ensure you get the most life out of your batteries.

Sound variant power

The version with sound needs a little more power to run the amplifier. Because of this you want at least 6V, but not too much more because of the extra heat that will be generated. Two lithium ion / polymer batteries in series (aka "2S") is probably the best solution for this.

A few final notes

When working with metal shrouds and parts it is important to remember that there are live connections on both sides of the counter. Care should be taken to ensure that the board is insulated from any metal parts.

When fitting the unit into your build it is easy to get confused with which wires are which. Label them. Don't get them mixed up. Connecting the battery to one of the button inputs will destroy the board. Take care.

For the version 4 board with sound I have made a handy wiring diagram showing how it all plugs together: