Step 1: Price and Supplies
(opt.) x2 $.48 8 pin IC socket
(opt.) $.99 14 pin IC socket
(opt.) $1.99 perf board (these 1.99-cheapies should have enough holes)
$1.99 piezo speaker (some higher dB speakers are more costly)
$1.49 .01 microfarad cap
$.99 10k ohm resistors (5-pack)
$.99 65k ohm resistors (5-pack)
$.99 100 ohm resistors (5-pack)
$2.99 CdS photoresistors (5-pack)
$3.99 5mm tactile switch
(opt.) $3.99 SPDT toggle switch
(opt.) $1.49 trimmer resistor
(opt.) $3.99 pager motor ("rumble" motor)
(opt.) $2.99 breadboard
$2.99 assorted LEDs (20 pack - cost effective if you want to make more suits)
$1.69 LM555 timer chip (8-pin)
$3.69 (@ Walmart) Laser pointer or bright flashlight (sensitivity will be explained in the build and explanation sections)
Wires and/or alligator clips, 9v battery clip
If you have ABSOLUTELY NONE of these parts these are the costs (not including batteries and wire).
If you have recovered from that price induced heart attack, remember it's only if you're missing everything, it goes down significantly if you have most of everything.
Step 2: Let's Build It! Part1: the First Chip
Step 1: Adding the heart and powering it.
In order for the circuit to work you'll of course need something to run your LEDs and Piezospeaker, but what fun is it to just apply power to them? Not very fun really, so we're using two LM555 timer chips to give our LEDs and speaker some style. Noting the clocking mark on the chips (denoted by a small dot or indentation) we hook up our first 555 timers' 8th pin to the power rail (the red colored column) and the 1st pin to ground using a jumper cable.
Step 2: Setting your trigger switch and reset threshold.
This laser tag system is actually comprised of two different 555 timer circuits. The main triggering circuit is called a bistable multivibrator or flip-flop circuit. The second triggered by the flip-flop activates a classic astable multivibrator to generate a tone. These are explained more in the next instructable step, so if you're not interested just skip over it. Now we'll set our "light switch" and reset button by first attaching a 10k ohm (10,000 ohms) resistor from power to your trigger pin (pin 2) on your first IC chip and a 65k ohm resistor from power to the reset pin (pin 4) on your first IC chip. Finally for this step we add the CdS cells (photoresistors) to the trigger pin (pin 2) in series (NOT PARALLEL!) directly to pin 6.
And... while we're on the topic of photoresistors, you may know that there are also many different sizes of photoresistors out there which each have different values in different light levels. The ones I used were 1/4" cells with 4 "ribs" (what I tend to call the wave-like line running through the center of the cell). In ambient light they create 3.35k ohms each (3,350 ohms) of resistance, 2.5M ohms (2,500,000 ohms) of resistance in total darkness, and 330 ohms of resistance when hit with the laser light. There are three other sizes I examined in CdS cells each with a different set of values (given in the order: Darkness, ambient light, laser light):
1/4" cell with 3 ribs: 2.5M ohm, 3.35k ohm, 330 ohm (our photoresistor being used)
1/8" cell with 4 ribs: 3M ohm, 5.38k ohm, 600 ohm
3/16" cell with 4 ribs: 1.4M ohm, 2k ohm, 400 ohm
3/32" cell with 3 ribs: (>= 10M) ohm, 4.2k ohm, 300 ohm
Step 3: Finishing our switches.
In the last step we had left off before we had actually finished the reset and trigger hookups. I did this because I wanted to keep the board relatively clean before we got in the way of our fun stuff and end up having a plate of spaghetti for a circuit board. Before we do the final jumper placements we must first add our light by taking it and connecting it from the output pin (pin 3) on the first IC to the ground rail (blue rail). Now we can add our tactile switch (push button) to our board. Connect your tactile switch to the reset pin (pin 4), using a jumper, and the other side of the switch to pin 6.
Step 3: Let's Build It! Part 2: the Second Chip
Step 1. Connect a 65K resistor from power to pin 7.
Step 2. Connect a 65K resistor from pin 7 to pin 2.
Step 3. Connect a jumper wire from pin 2 to pin 6.
Step 4. Connect a .01 microfarad capacitor from pin 2 to ground.
Step 5. Connect piezoelectric buzzer to pin 3 with a jumper wire and connect the buzzers ground to ground with a jumper wire.
You have now completed the tone generating setup. Congrats!
Step 4: How This Circuit Works
Whew, that's quite easy once you see it in action more. This is how we get our alerting tone when we hit the mark, but how does it turn on and off when you hit the trigger? The output of the first 555 timer chip controls the power for the second chip. When the no light hits the target, the chip sits in a reset/off position and does not put out a voltage that the second chip can work off. When the target is hit, however, the voltage produced at pin 3 is about 3 volts, so the other chip can now work off of that voltage . Now that it can work, the tone is generated by the resistors and capacitor.
The first chip is set up as a Schmitt Trigger that changes it's state depending on whether the Threshold is high or low. The threshold is set at pin 6 by a 1/3:2/3 signal by either the reset pin or the trigger pin (respectively) caused by variances in resistance (with our photoresistor) or by switch (with our reset button). A current that is 2/3 of the original source current must be applied to pin 2 for the chip to set a threshold in a high state while a 1/3 source current must be applied to the reset pin for the threshold to be set to a low state. In either case, the threshold state is kept until the opposing condition is met, which explains why the chip keeps the LED on or off over a length of time.
If you really want to learn more about the 555 time chip I suggest borrowing Electronics for Dummies from a library or buying it in a bookstore and turning to chapter 7. (photos below are the circuit posted on page 161 and 164 in Electronics for Dummies.)
Step 5: New Step - the Laser Gun Circuit
Step 6: The Supplies and Some Explinations
$1.29 - 100 mircofarad capacitor
$1.19 - 1 microfarad capcaitor
$0.99 (5-pack) - 100 ohm resistor (Color bands: brown, black, brown)
$0.99 (5-pack) - 470 ohm resistor (Color bands: yellow, purple, black)
$0.99 (5-pack) - 10k ohm (10,000 ohms) resistor (Color bands: brown, black, orange)
$0.99 (5-pack) - 22k ohm (22,000 ohms) resistor (Color bands: red, red, orange)
$0.79 (each) x2 NPN transistors (The ones I used were Radioshack 2N4401's)
($30+ dollars at Radioshack, find one at a cheap dollar store) Laser light
$1.49 - Light Emitting Diode (LED)
A few things you should know before you tear your hair out over not having the supplies. There are quite a few things you can change about. One thing you can change would be the 2N4401 NPN transistors. To my understanding of the circuit you can use any NPN transistors (3904, 2222, 4401, etc.) as long as they are NPN . If they aren't you may burn something out or it just plain won't work (As a tip to those who don't know if their transistors are NPN or PNP, simple use this circuit with two LEDs and your transistors in question. If the LEDs flash the transistors are NPN. If you end up using two PNP transistors the circuit won't work and there shouldn't be a risk of burning out the components.)
Another thing you should know is that you don't really need the LED in the circuit but it (A) shows if your circuit is hooked up correctly and (B) could be used for cool lighting effects on your ray gun. You may not have all the necessary resistances either but before you hit your head on the desk at the lack of parts you can simply use the power of tens to exchange the equation (Sorry, I don't know the math for this circuit...yet) but if you use a 100k ohm (100,000 ohms) resistor you may want to use a .1 microfarad capacitor (explained later on in the build).
Step 7: The Shortest Part: Building
Starting off the board we plug in our two NPN transistors (on most if not all NPN transistors reading the pins left to right, flat side facing you, the pinouts are Emitter, Base, and Collector.) into the board.
Then you take your 100 ohm resistor and plug it from power to a random open place in your board which will later be bridged with your laser circuit (trust me, it's better for the sake of anti-spaghetti-plateness). We then take our LED and connect its anode (positive side) directly to power and its cathode (negative end) to a spot on the board. Immediately after that, place a 470 ohm resistor from the cathode to the Collector (With flat side facing you: the farthest right pin) of one of the transistors (just for my own preference, I used the right side transistor), this is what we'll eventually be doing to the laser light. Next, place our 100 mircofarad capacitor so that the anode (positive end) connects to the collector of transistor with the LED connected and the cathode (negative end) will connect with the base of the other transistor. We then reverse this process with the 1 microfarad capacitor by attaching its anode to the collector of the no-LED transistor and the cathode to the LED-transistor's base . Now that the most complicated part (yes, that was the most complicated part) is over we take our 10k ohm (10,000 ohm) and connect it to power and the base of the no-LED transistor and then connect a 22k ohm (22,000 ohm) resistor to power and the base of the LED-transistor. Semi-finally connect the emitters (the only pins you haven't touched) to ground using jumper wires. Now, finally, we take our beloved laser light and plug that puppy between the 100 ohm resistor and the collector of the formerly no-LED transistor. To give the circuit power we make a connection from the positive end of the 9v battery and the N.O. terminal (that's normally open when you're talking about switches) and connect the common ground (the lonely pin at the bottom) to the power rail on the board and finally connect the ground rail to the negative terminal of the battery and you're all set.
Step 8: How the Ray Gun Works
If you're interested post your creations for other Instructable-ites to view and have fun! Stay tuned for the enclosed version of the system.