Question I want to register a small change of voltage of a photo sensing diode at bullet's speed ?

Jun 24, 2021
What I intend to do:
Estimate Accuracy of a Bullet Hit from the Bull's Eye

Use some light sensing diodes like BPW34 (or you suggest) spanning a feet vertically and horizontally or so with laser light incident on them from above and side respectively. When a bullet is fired between the laser and the diodes it will interrupt the incident light on any one of the horizontal and vertical diodes at speed of approximately 2700 km/hour (average bullet speed). This will cause a change of voltage/current values of the diodes that shall be registered, 7.2 μs response time depending upon surface area of BPW34 diode.

Problem Areas:
  1. Suggest a Light Sensing Diode whose response time of light interrupt can produce a noticeable change in voltage/current at above speed.
  2. Which amplification circuit (Op-amp ) is required which can amplify the change in incident light level.
  3. What comparator circuit to be used which can record the change and register it for processing.

    Last but not the least: I am a starter at electrical circuits.
While I'm not sure how you would monitor accuracy with such a setup (it sounds like a camera and motion capture software like MLB uses would be much more accurate--and harder to accidentally shoot), it seems remarkably similar to the traditional ballistic chronographs using skyscreens. Those inexpensive commercial products do use two light sensing diodes to watch for the shadow of the bullet.

More recently there's the Magnetospeed which actually senses the bullet travelling through a magnetic field, or of course the LabRadar which just sits on a table and is pointed downrange.
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