Trigger trap – Photo-spectrum Services

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 and 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 controllable directly and remotely through a phone app. I have not used this system.

A passive infrared (PIR) sensor does not measure the distance, works only warm-blooded animals and has a broad angle of view. Its main advantage is the low power use.

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 in 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, but still-feature rich ones have become extremely cheap ($\approx$ 5 to 15 €).

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, although 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 €) with 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. It would be interesting to also test if a radar human prescence sensor could could be used in place of the PIR sensor.

How to

To start working on this project, I bought a LiDAR sensor and two millimeter wave Radar sensors of human presence/movement. I do already have some SBCs and power supplies that I can use. Static LiDARs with a single laser beam have a narrow field of view (FoV), usually less than 3 degrees. Radars have a broad field of view, usually from 60 to 75 degrees. Both LiDARs and Radars can measure distances

A catch with LiDAR is that as it used IR radiation it can be disturbed by sunlight. Sunlight decreases the range to different extents depending on the sensor design. The maximum range of the cheap LiDAR sensor TF-Luna ($\approx$ 30 €) from Benewake, is 8 m indoors. More expensive ones like the TFmini-S ($\approx$ 40 €) reach to 12 m indoors. There is also an IP65-encased version the TFmin Plus ($\approx$ 50 €) at a higher cost. There are also sensors sold by better-known suppliers like Garmin’s LIDAR-Lite v4 sensor available, for example, from SparkFun rated at 10 m ($\approx$ 65 U$s in the USA, but $\approx$ 150 € in Europe). Recently a new LiDAR sensor has appeared in AliExpress under multiple brands and model types. Photographs are identical, so the hardware seems to be the same for all of the. Specifications are also the same but supporting software varies. Benewake calls it TFS20-L ($\approx$ 50 €) it has a range of 20 m indoors and 12 m in sunlight. This is much better than the TF-Luna, but it is a bare sensor and more expensive. However, what looks like the same sensor is also sold as PolarisIC DTS6012M ($\approx$ 18 to 40 €). From PolarisIC web site it looks that this is the manufacturer. The data sheets from Benewake and PolarisIC are almost identical except for brand name.

I ordered one PolarisIC DTS6012M. It has both I2C and UART interfaces. The distance resolution at distances shorter than 6 m is $\pm 3\,\mathrm{cm}$ and FoV < 2 degrees.

I ordered two different radar sensors that are able to report distance. The ability to measure distances and total inmunity to ambient light could make them better than a PIR sensor if the parameters can be tuned to detect birds and animals smaller than a human. Their reach is less than that of the LiDAR, but not by much in sunlight. The sensors are a Waveshare HMMD mmWave and a HiLink LD2412S. Both, the mmWave and the LD2412S sensor, have a serial interface at 3.3 V. These sensors have different reach for static and moving humans. In the case of “static” humans breathing movements are detected. The detection range is more for moving subjects than for static ones. According to specifications, the LD2412 has a range of 9 m and a resolution of about 1.5 m and FoV 75 degrees. The mmWave has a range of 10 m and a distance resolution as good as 0.15 m with FoV of 45 degrees.

As interfaces to a PC I will use for initial testing Yocto-Serial and Yocto-I2C USB modules from YoctoPuce. Recent SBCs I have are ESP32-C3 ($\approx$ 3 to 5 €) and ESP32-C6 ($\approx$ 7 to 12 €) generic boards with dual USB-C sockets, older ones, but still readily available, are Olimexino-328 ($\approx$ 25 to 30 €) from Olimex and an Arduino Leonardo ($\approx$ 20 to 25 €) from Arduino. These four SBCs are supported by the Arduino IDE.

To test and program specific settings in the sensors using the Windows software from HiLink and Waveshare USB to serial (3.3V) I will the use interfaces HiLink KLK-CH340E and Waveshare CP2102. I do have a third one based on FT232 but the modules cannot be powered from it.

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 and while the trigger is active. 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” (detection by the LiDAR is this case).

Note

A built-in trigger-trap mode could be a nice addition in a future firmware or camera model. However, it would most likely drain the battery very fast.

Reuse

CC BY-SA 4.0

--- title: "Trigger trap" subtitle: "Hardware and software" author: "Pedro J. Aphalo" date: "2025-05-24" date-modified: "2025-08-05" toc: true categories: [cameras] keywords: [trigger trap, LiDAR, shutter trigger] format: html: code-tools: true lightbox: auto license: "CC BY-SA" draft: true --- ## Introduction There exist different possible approaches to setting up a trigger trap. [Hähnell's Captur Module Pro + IR-module](https://www.hahnel.ie/irish-shop/captur_module_pro/) ($\approx$ 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 and 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](https://www.miops.com/products/smart) ($\approx$ 300 €) based on similar detection approaches, but controllable directly and remotely through a phone app. I have not used this system. A passive infrared (PIR) sensor does not measure the distance, works only warm-blooded animals and has a broad angle of view. Its main advantage is the low power use. Cognisys' [Sabre II](https://cognisys-inc.com/sabre-2.html) trigger is based on a LiDAR, which has many advantages, but costs 500 u$s, which given its capabilities, seems very reasonable compared to the MIOPS. A LiDAR is based on reflected IR radiation and able to measure distances, making it possible to limit triggering to a range of distances of interest. A LiDAR, in addition, does not require a separate IR source. The Sabre II is also very fast, and usable even for birds in flight. Additionally, it has a built in PIR sensor that can be used to enable the LiDAR only when there is an animal within a broader target range, saving power. LiDAR sensors are nowadays very common components as they are used in most drones and robots. They come in a wide range of prices and with different distance reach. This raises the question about the possibility of building a cheaper LiDAR-based camera-trap trigger. The most powerful single board computers (SBCs) have become very capable although rather expensive, while the lowly, but still-feature rich ones have become extremely cheap ($\approx$ 5 to 15 €). ## An Arduino-based alternative [Paul Illsley](https://paulillsley.com/) has published [a design for a LiDAR trigger based on a cheap LiDAR sensor an a Arduino UNO SBC](https://paulillsley.com/arduino/lidar_camera_trigger.html) among other interesting [Arduino-based projects related to photography](https://paulillsley.com/arduino/). The trigger described by Paul Illsley uses a [TF-Luna LiDAR sensor](https://en.benewake.com/TFLuna/) from [Benewake](https://en.benewake.com/) 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](https://en.benewake.com/TFminiPlus/index.html) with a range of 12 m and IP65 protection would be a better choice for field use, although at about twice the price. The design described by Paul Illsley uses an [Arduino UNO R3](https://store.arduino.cc/products/arduino-uno-rev3) 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](https://store.arduino.cc/products/arduino-nano) ($\approx$ 25 €). Very small SBC's based on different microcontroller families such as ESP32-C3 ($\approx$ 5 €) or ESP32-C6 ($\approx$ 10 €) with 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](https://www.raspberrypi.com/products/raspberry-pi-zero/), [Raspberry Pi Zero 2W](https://www.raspberrypi.com/products/raspberry-pi-zero-2-w/), [OrangePi Zero 2W](http://www.orangepi.org/html/hardWare/computerAndMicrocontrollers/details/Orange-Pi-Zero-2W.html) or even [Raspberry Pi Pico](https://www.raspberrypi.com/products/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. It would be interesting to also test if a radar human prescence sensor could could be used in place of the PIR sensor. ::: {.callout-warning icon=false} # {{< fa screwdriver-wrench >}} How to To start working on this project, I bought a LiDAR sensor and two millimeter wave Radar sensors of human presence/movement. I do already have some SBCs and power supplies that I can use. Static LiDARs with a single laser beam have a narrow field of view (FoV), usually less than 3 degrees. Radars have a broad field of view, usually from 60 to 75 degrees. Both LiDARs and Radars can measure distances A catch with LiDAR is that as it used IR radiation it can be disturbed by sunlight. Sunlight decreases the range to different extents depending on the sensor design. The maximum range of the cheap LiDAR sensor _TF-Luna_ ($\approx$ 30 €) from Benewake, is 8 m indoors. More expensive ones like the _TFmini-S_ ($\approx$ 40 €) reach to 12 m indoors. There is also an IP65-encased version the _TFmin Plus_ ($\approx$ 50 €) at a higher cost. There are also sensors sold by better-known suppliers like Garmin's LIDAR-Lite v4 sensor available, for example, from [SparkFun](https://www.sparkfun.com/garmin-lidar-lite-v4-led-distance-measurement-sensor.html) rated at 10 m ($\approx$ 65 U$s in the USA, but $\approx$ 150 € in Europe). Recently a new LiDAR sensor has appeared in AliExpress under multiple brands and model types. Photographs are identical, so the hardware seems to be the same for all of the. Specifications are also the same but supporting software varies. Benewake calls it TFS20-L ($\approx$ 50 €) it has a range of 20 m indoors and 12 m in sunlight. This is much better than the _TF-Luna_, but it is a bare sensor and more expensive. However, what looks like the same sensor is also sold as PolarisIC DTS6012M ($\approx$ 18 to 40 €). From PolarisIC web site it looks that this is the manufacturer. The data sheets from Benewake and PolarisIC are almost identical except for brand name. I ordered one PolarisIC DTS6012M. It has both I2C and UART interfaces. The distance resolution at distances shorter than 6 m is $\pm 3\,\mathrm{cm}$ and FoV < 2 degrees. I ordered two different radar sensors that are able to report distance. The ability to measure distances and total inmunity to ambient light could make them better than a PIR sensor if the parameters can be tuned to detect birds and animals smaller than a human. Their reach is less than that of the LiDAR, but not by much in sunlight. The sensors are a _Waveshare HMMD mmWave_ and a _HiLink LD2412S_. Both, the mmWave and the LD2412S sensor, have a serial interface at 3.3 V. These sensors have different reach for static and moving humans. In the case of "static" humans breathing movements are detected. The detection range is more for moving subjects than for static ones. According to specifications, the LD2412 has a range of 9 m and a resolution of about 1.5 m and FoV 75 degrees. The mmWave has a range of 10 m and a distance resolution as good as 0.15 m with FoV of 45 degrees. As interfaces to a PC I will use for initial testing Yocto-Serial and Yocto-I2C USB modules from [YoctoPuce](https://www.yoctopuce.com/). Recent SBCs I have are ESP32-C3 ($\approx$ 3 to 5 €) and ESP32-C6 ($\approx$ 7 to 12 €) generic boards with dual USB-C sockets, older ones, but still readily available, are Olimexino-328 ($\approx$ 25 to 30 €) from [Olimex](https://www.olimex.com) and an Arduino Leonardo ($\approx$ 20 to 25 €) from [Arduino](https://www.arduino.cc/). These four SBCs are supported by the Arduino IDE. To test and program specific settings in the sensors using the Windows software from HiLink and Waveshare USB to serial (3.3V) I will the use interfaces HiLink KLK-CH340E and Waveshare CP2102. I do have a third one based on FT232 but the modules cannot be powered from it. ::: ## 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. ::: callout-attention 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 and while the trigger is active. 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" (detection by the LiDAR is this case). ::: callout-note A built-in trigger-trap mode could be a nice addition in a future firmware or camera model. However, it would most likely drain the battery very fast. :::