Introduction
There exist different possible approaches to setting up a trigger trap. Hähnell’s Captur Module Pro + IR-module (\(\approx\) 90 €) is versatile, and capable of detecting different events: sound, light and blockage of the line of sight between a laser or IR LED and a detector. For a trigger trap to photograph animals, this last approach is most useful. However it makes it necessary to set the trigger and/or laser pointer or NIR LED emitter away from the camera. Hähnell sells remote wireless receivers usable both as flash and camera-shutter triggers in versions suitable for different brands of cameras ana flashes. I have owned this trigger system for several years and used it with different OM-System/Olympus cameras, and Olympus and Godox flashes. MIOPS sells the Smart+ Versatile Camera Trigger (\(\approx\) 300 €) based on similar detection approaches, but controlable directly and remotely through a phone app. I have not used this system.
A passive infrared (PIR) sensor does not measure the distance…
Cognisys’ Sabre II trigger is based on a LiDAR, which has many advantages, but costs 500 u$s, which given its capabilities, seems very reasonable compared to the MIOPS. A LiDAR is based on reflected IR radiation and able to measure distances, making it possible to limit triggering to a range of distances of interest. A LiDAR, in addition, does not require a separate IR source. The Sabre II is also very fast, and usable even for birds in flight. Additionally, it has a built in PIR sensor that can be used to enable the LiDAR only when there is an animal within a broader target range, saving power.
LiDAR sensors are nowadays very common components as they are used in most drones and robots. They come at a wide range of prices and with different distance reach. This raises the question about the possibility of building a cheaper LiDAR-based camera-trap trigger. The most powerful single board computers (SBCs) have become very capable although rather expensive, while the lowly ones, but still-feature rich ones have become extremely cheap (\(\approx\) 5 €).
An Arduino-based alternative
Paul Illsley has published a design for a LiDAR trigger based on a cheap LiDAR sensor an a Arduino UNO SBC among other interesting Arduino-based projects related to photography.
The trigger described by Paul Illsley uses a TF-Luna LiDAR sensor from Benewake which is available for between 20 € and 30 €. It has a maximum range of 8 m, and has no weather protection. I think, the TF-mini Plus with a range of 12 m and IP65 protection would be a better choice for field use, althrough at about twice the price. The design described by Paul Illsley uses an Arduino UNO R3 SBC (\(\approx\) 20 €), which has a relatively large form factor. It could be substituted by a similar board with a smaller form factor such as the Arduino Nano (\(\approx\) 25 €). Very small SBC’s based on different microcontroller families such as ESP32-C3 (\(\approx\) 5 €) or ESP32-C6 (\(\approx\) 10 €) vwith low power consumption could be used as long as suitable libraries for the Arduino IDE are available. Of course, SBCs based on other more capable microcontrollers, but still small in size like the Raspberry Pi Zero, Raspberry Pi Zero 2W, OrangePi Zero 2W or even Raspberry Pi Pico could be also used.
To build a system with all the features of the Sabre II would most likely be nearly as expensive as buying a Sabre II and take a lot of time to build, test and program. However, building a system with fewer features and a shorter range would probably be cheaper and provide a good learning experience about modern remote distance and positioning systems. This last point is the main reason for me to try this.
Mounting the LiDAR sensor
The alignment of a LiDAR is critical if it has a narrow angle of view, such as 3.6\(^\circ\), and the Olympus 300 mm 1:4 MFT telefoto lens has an angle of view of 4.1\(^\circ\).
One approach would be to mount the trigger on the flash hot shoe of the camera. Good and stable alignment would require a good fit of the LiDAR trigger to the flash hot shoe of the camera. This is possible, I expect, with Olympus/OM System cameras as their flash hot “shoe” has an alignment pin. Building a trigger with this approach would require an Olympus compatible flash “foot” with a compatible alignment pin. Adding a laser pointer aligned with the LiDAR as used in the Sabre II trigger would be of great help in practical use if visible in day light.
Alternatively, the LiDAR trigger could be mounted separately, and the camera triggered wirelessly, using, for example a Hähnell remote trigger transmitter and receiver pair. This can be easily done as the Hähnell transmitter has a socket for connecting an external release switch.
To obtain a suitable hot shoe, probably the best approach would be to buy a spare part for a Godox flash for Olympus cameras as these are readily available and cheap (\(\approx\) 10 €). These flash hot-shoe bases for Olympus cameras do have an alignment/lock pin.
OM-1 use with a trigger
The PIR or millimeter wave Radar sensor could be used to not only enable the LiDAR sensor but also to enable a “half-press” of the shutter release. With the camera set to subject recognition and/or focus tracking, and ProCap2 mode, this would enable focusing the camera if in auto-focus mode and start filling the camera image buffer, so that images would be captured both immediately before the trigger enables the “full-press” of the shutter release based on the LiDAR. The number of photographs to save both before and after the shutter is “released” can be controlled by the camera settings in case of a long uninterrupted “full press”.
A built-in trigger-trap mode could be a nice addition in a future firmware or camera model.