Digital counter

[Matt_K]

Firstly hi everyone,

This is my first post, I'm not very expereinced in electronics but in the quest for a summer project i am starting to delve in.

Basically what I want to build is an ammo counter for an electric airsoft gun. (like the pulse rifle in aliens)

I have found some electronics kits available, but none that do what i think the project will need.

As i understand it I want to build a counter that:

• Starts at 99 and counts to 0 (Each magazine holds 99 bbs)
• Has a switch to reset it to 99 (For when i load a fresh magazine)
• Has a mechanism to detect when a single bb has been shot out the barrel, either by a switch in the gearbox or some kind of IR beam across the end of the barrel

Have any of you guys done anything like this before?

Or do could you point me in the direction of a resource that could help?

Many thanks
Matt

 

[House0Fwax]

For the count down, look into the 40110 chip, it drives a 7 segment LED display and counts either up or down. (You'd need two.)

As far as the IR beam goes, that should be just a quick Google away.

 

[Boncuk]

Hi Matt,

the CD40110 would do the job, but reset is always done by zeroing the outputs.

I understood you want to indicate the remaining rounds of ammo when the gun is loaded - 99 (instead of 00) and count down.

Therefor I suggest to use a programmable binary U/D counter (74LS192). That one can be preset and loaded to any value.

Using a CD40110 you would save one IC per digit (contains a 7-segment decoder already), but indicating a false value. Starting at "00" the first trigger pulse would set it to "99" which is acutally "98", since one of 99 shots is already fired. (or fire one shot without ammo before loading )

To trigger the counter the gun has some means of triggering a "bullet". If it's electronic that would be perfect, using the same signal to trigger the counter.
If it's mechanical the easiest way to trigger the counter would be a tiny microswitch (or a reed switch, magnetically activated) to attach to the trigger.

Please decide on the choices offered and also make a short describtion of the gun trigger mechanism.

Hans

 

[Matt_K]

Thank you for the help chaps.

I'm trying to have to try out a few different designs for the trigger mechanism, mainly because the gun will fire on full auto (A constant current is fed to the motor which turns a gearbox repeatedly loading and shooting bbs).

As the current to the motor will be constant rather than in pulses i assumed that I couldn't use this as an input to the counter.

So I am looking at different ways to install a switch inside the gearbox that will detect 1 complete cycle. My only concern is that the gun fires at about 7-8 shots a second so I will need to make the switch quite robust.

Thanks again, I'll have a look at those parts you suggested.

 

[Boncuk]

Hi Matt,

using a motor to load the gun for rapid firing sequence (continous fire) won't make a difference using the counter ICs.

As you will certainly use a reduction gear and a kind of ammo drum (as used in gatling guns) that one could be used in conjunction with a coded disk and an IR-barrier chip (as used to determine x and y travel in a computer mouse).

The disk has to be big enough in diameter to mount transmitter and receiver on both sides of the disk (mounted like a fork) and pulses will be generated when holes in the disk allow unrestricted view of the receiver to the transmitter.

For proper function it doesn't make a difference if the receiver has steady view on the transmitter while nothing moves. Only pulse transitions from high to low and vice versa will be recognized as count pulses.

I suggest to get the mechanical part done first and then adapt the electronics accordingly. Just a view look ahead properties should be contained in the mechanical design.

Hans