DIY Airsoft Chronometer/ Chronograph, PC based (Part 2- Construction)

Circuit diagram. Reverse polarity of the diode will not burnt the diode as the reverse voltage is not high enough to damage it. Make sure your mic input support stereo input. Most P4 or above motherboard has stereo mic.
IR diode is quite resistant to ambient light. U may cover the receiver diode if U found too much noise. Make sure all connection is solder well as small vibration may produce noise in the wave capture in Audacity. Get the orientation of which one is the entry reciever diode end, by testing each channel in the Audacity tracing.

IR sender diode connect in parallel with a battery source. The specified nominal voltage of my 5mm IR diode is 1.7V at 20-200mA. So I use 3V lithium battery with a voltage drop resistor. So 10-100 Ohm 0.5W resistor is ok. Note the polarity of the diode. The smaller metal piece inside the diode is to be connected to the battery positive.

For the IR recevier diode, one of the pin of the entry and exit diode is connected to the stereo plug middle and tip segment respectively (provide 2 channel information . The ground (base of the stereo plug) is connected to the other pin of each diode.

I check the IR sender by using my Sony DV camera. One should see the IR sender diode is lit on.

The IR receiver diode can be checked by using any TV/HiFi/DVD remote controller. One can see the IR spike on the Audacity software.

For small velocity gun, the tracing is easy to be capture. For higher velocity gun, a single exit diode may not be able to capture the signal in just 1 shot, as the BB may pass the exit diode on sideway. U can enhance this limitation by adding more parallel IR receiver diode in the exit end - a curtain of IR that will not miss the BB.

Audacity Software setting .... (to be cont)