 | Intro |  |
This page outlines the material, design and procedure for my bullet counter
modification on my G36C airsoft rifle. By no means is it a guide or a
how-to. Though anyone with junior electronics and carpentry skills can
perform the same mod with ease and I hope that this will be a place to
spark interest for those who are interested. | Planning | |
- IR Emitter and sensor to detect bullet leaving barrel
- 74HC14N to stabilize IR sensor's trigger and send TTL signal to counter
- counter circuit 74LS90 and 74LS47 (times 3 digits) to drive 7 segment LED display
- 5V regulator to take power from 8.4v main battery pack
After hooking everything up, I realized that the current draw on the rifle's electric motor is far too much, and while firing there isn't enough current to power the counter.
5v power supply
IR
sensor circuit
The original plan was scrapped, and a new circuit was built:
- IR Emitter and sensor to detect bullet leaving barrel
- 74HC14N to stabilize IR sensor's trigger and send TTL signal to counter
- counter circuit LM14553 and LM14511
- External batteries (1.2v x 4)
New counter circuit (http://members.shaw.ca/roma/three%20digits.html)
- Couldn't find MC1543, ended up using the MC14511 instead
- The .4nF capacitor doesn't need to be installed so that the faint signal
from the speeding BB pellets can be registered and not treated as noise
The new circuit was built with the hopes that since the CMOS IC has much lower voltage requirement, it can still operate when the rifle is firing, but I was wrong. :( Though my second alternative is to use external batteries, and power consumption is an important factor in this case.
As far as power goes, the new circuit uses the Motorola 14533 CMOS to multiplex the three digit displays which saves a lot of energy from having to power all three digits at the same time. Only one LED driver is needed because of that instead of three.
| Labor | |
Like any electronic projects, the concept had to be proven with the design
stuck on the breadboard. My left hand held a piece of paper blcking the
infrared emitter and the number went up. Now to start with the installation.
A latch switch is slipped at the end of the decorative cocking rail, so
pulling the cocking lever back will turn the counter on and off.
Originally, the infrared transmitter and receiver was mounted in the path
where the bullets were being fed, but as it turns out, since bullets are fed
before the actual shots are fired, the display wouldstart counting
before the actual shots are fired.
The sensor ended up being installed at the nozzle. A 1/16" hole needed
to be drilled through the flash suppressor. After testing, the tape was
removed and glue + black paint was used to secure and hide the infrared
emitter/receiver.
The tiny space right below the rear sight is used to house the 5v power
supply.The chip dangling in front of it is the 74HC14N used to detect
the infrared receiver and send a clean signal to the counter circuit.
As opposed to soldering on a circuit board, I had to solder everything
together with wires because of the space restrictions. First
version requires three of these counter/driver pairs, making 6 chips
to install. The second version
only requires two chips but needed a few transisters and resisters on the side.
First version of the counter was mounted on the side, hence the little transparent window
was built on the side also. It's not as functional but is great for showing
off. :) The empty area inside the handle is where the circuit is stored.
Otherwise there is no other space in the rifle to hide the circuit.
The LED display (2 digit on both sides) plus the circuit all tightly wrapped.
On the second version a much smaller digit display was used, allowing three
digits to be stacked inside the top handle. Though not as flashy it's
much more practical.
Watching the numbers climb while spraying in full auto mode is pure joy.
Questions? Comments? Click here to contact me, or just sign my guestbook. ;).
Lanzer (Jan '05)