I found a pistol shape broken RC car remote from my son’s toy box one day and got an idea to modify it into a toy laser gun. I also had a cheap laser pointer. I regret for forgetting to take pictures of all intermediate procedure.
As you can see, the antenna was removed and an aluminum tube (about a half inch OD) as a barrel was added. The laser diode assembly and the triggering circuit and two supercaps for power supply are all integrated inside the handle as shown in the picture below.
The laser diode for a laser pointer needs about 3-5VDC, so my idea was to provide 5V to the laser from two supercap (10F, 2.7V) in series and charge the supercaps through USB female connector. You can fully charge them from a computer USB port in 20-30 seconds (not minutes or hours!). Of course the supercap’s capacity is much smaller than other rechargeable batteries, but it can hold sufficient amount for playing with your kids for long enough with one charge. I made a circuit to supply only a short pulse of power to the laser when it is triggered by a tactile switch attached behind the yellow trigger.
As explained, there is a USB connector and two supercaps are connected directly to the +5V and GND pins of the USB connector so that they can be charged whenever you plug it in to any USB port of a PC or a wall wart USB charger. In the diagram, I added a power switch, but I didn’t actually use it because it could charge so fast that you don’t have to try to save power when it is not used. And in fact, even if you cut the power line to avoid discharging by the circuit, you cannot completely prevent discharging 100%. You may have experienced with old flash lights.
Let me talk about how it works.
- First of all, if the supercaps are charged (and power switch is closed), the capacitor C3 (electrolyte capacitor, 470uF, 6.3V) is instantly charged because it is connected to the supercaps through the normal close pin of a small relay, K1 (5V).
- When the trigger switch is closed, the relay, K1, is activated and the charge from the capacitor, C3, discharges to the laser. You can change the length of the laser pulse by changing the capacitor, C3, e.g. 200uF for shorter pulse or bigger ones for longer pulse.
- Once you release the trigger, the relay will be deactivated and the capacitor, C3, is charged again.
It’s simple but solid way to generate a laser pulse, isn’t it?
For more detail pictures, visit my Flickr Photoset .
Inside the target box, there are a power switch at the top left corner; a piezo buzzer at the top center; a CdS to receive laser beam (a red plastic (taken from a push switch 🙂 at the center of the target (see above picture) is used to filter only (mostly) the red laser beam); a circuit board for switching the buzzer triggered by the CdS; and 5) two D battery holder in the picture below.
The circuit is very simple. A general purpose NPN transistor, 2N3904, works as a switch. Two batteries (3V) power the whole circuit. If the laser hit the center of the target, the CdS cell will decrease its resistance and the base current of the transistor will be increased. As a result, the transistor will be ON and the buzzer will set off. That’s it.
You can find more detail pictures from my Flickr Photoset