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Assembly and Operating Instructions for Kits


Operation of the Dual Light Sensor


Assembly instructions for other kits


Click on any photo to enlarge.

Dual Light Sensor

Figure 1

Dual Light Sensor control box

Sensor cable Emitter cable

Figure 2

Sensor cable

Figure 3

Emitter cable


RCA flash trigger cable, assembled

Nikon MC-30 shutter cable

Figure 4

Flash trigger cable

(RCA type)

Figure 5

Shutter cable for camera

(photo shows cable for a Nikon camera)



The Dual Light Sensor (DLS) has two modes that allow one to trigger flash or camera on either the presence or absence of light. The Dual Light Sensor also works in combination with a Delay Timer in order to delay the discharge of the flash or actuation of the camera shutter. The Dual Light Sensor kit comes with all the parts for the control box (Figure 1), the sensor cable (Figure 2), and the emitter cable (Figure 3). The flash trigger cable kit (needed for triggering a flash unit) and the shutter cable (needed for triggering a camera shutter) are purchased separately.


Powering the DLS

The DLS can be powered with either a 9-V battery or an optional 9-V wall transformer. If using a transformer, simply plug it into the Power In port. If a battery is also installed, the transformer power will bypass the battery. The advantage of using the wall transformer is for applications where the Dual Light Sensor will be on for extended periods of time, and the supply voltage must be maintained. If using a battery, begin the installation by removing the 4 corner screws holding the lid to the box. Lift off the lid carefully. Insert a fresh, 9-V battery into the battery holder, making sure that the contacts snap securely to the battery. If desired, the battery holder can be removed to help with the installation. Velcro connects the holder to the box. If removing the battery holder, be careful not to stress the red and black wires to the lid. When the battery is installed, close the lid carefully to make sure not to pinch any wires between the lid and the case. Then screw the lid back on.

With the battery installed or the wall transformer connected, flip the power switch to the ON position. The Power LED on the left side should light and remain lit.


Note that the circuitry of the DLS is protected from overload by a 1A fuse. In event that the power LED doesn't come on when the DLS is switched on and the battery is fresh, check the fuse inside the box for integrity. Replace the fuse, if needed, with a fuse having a rating of 1A.


The Sensor and LED cables

The two cables needed for full operation of the DLS are shown in Figures 2 and 3 above. Note that the sensor end of the sensor cable has a clear, plastic case, while the infrared LED emitter on the LED cable has a blue, plastic case. It’s important to distinguish between these two cables, because they plug into different jacks on the box. These jacks are labeled Sensor and LED. We recommend turning the power to the box off before inserting the cable plugs into the jacks. If you happen to insert the cables into the wrong ports, you likely won’t hurt anything, but, of course, the unit won’t work correctly. In the event that longer cables are needed for an application, you can use 3.5mm mono male-female cable extenders.


The Ready Mode Switch
The Ready Mode Switch is used to switch between the two triggering modes of operation, labeled Light and Dark. Note that the switch has 3 positions. The center position is an open circuit in which neither mode is operational.  Here is a description of the two modes.

  • Light: The unit triggers when the intensity of light detected by the Sensor increases above a particular threshold. The latter is determined by the position of the Sensitivity knob.
  • Dark: The unit triggers when an infrared beam is blocked. The sensitivity knob is used to adjust for the ambient light level as well as the separation of the infrared light source and detector.

Operation of the two modes is described next.


The Dark Mode
Both the Sensor and LED cables are needed for the Dark mode of triggering. In order to test the operation of the trigger, carry out the steps below.

  1. Plug in both cables and then tape them a few inches apart on a table and facing each other as shown in Figure 6 below. An infrared beam passes from the LED to the sensor but, of course, you won’t see it, since infrared has a frequency below the range of visible light. Have the room lights on initially.
  2. Flip the Ready Mode switch to the Dark position. (Be sure the switch moves one click past the center position.) Set the Sensitivity at the 2 mark and turn on the box.
  3. With the Sensor and LED aligned, the Ready LED should be lit. If not, adjust the alignment to make sure that the LED is aimed at the Sensor.
  4. Place a finger between the Sensor and LED (we’ll call this the gate) while watching the Ready LED. The latter should go out, indicating a blockage. Lift your finger up to see that Ready LED turns back on. Now try running your finger through the gate without stopping. The Ready LED should blink off when your finger is in the beam.
  5. Note that if you turn the Sensitivity down to 0 (try this), the Ready LED will may go out. This depends on how bright the ambient light is. It’s typical not to set the Sensitivity less than 2.
  6. Now turn the Sensitivity up to 10. When you run your finger through the gate, you may not notice any change in the Ready LED. This happens when the room is bright and the Sensitivity is turned high. Turn down the Sensitivity slowly while holding your finger blocking the gate. At some position, perhaps around 5, the Ready LED will go out. Now remove your finger. The LED should come back on, indicating correct operation. What you’ve done is locate the position of greatest sensitivity for your combination of room light and gate width. (We’ll show you in a later step the effect of gate width.) We recommend that as a default setting, you use the position midway between 2 and the point of maximum sensitivity. That’s because the point of maximum sensitivity can drift, depending on ambient light and the battery level. If you do operate at or near maximum sensitivity, keep in mind that if the gate stops working, you probably need to make an adjustment.
  7. Turn out the room lights now. (You can have a dim light on in order to see what you’re doing.) When the room is dark, you can turn the sensitivity up higher. Try it to see how high you can turn the sensitivity.
  8. As a final test, increase the gate width (separation of Sensor and LED). Leave the room lights turned down and sensitivity turned up.  Leave the Sensor taped down but untape the LED. Just move the LED further away by hand. Move the LED, say, a few inches at a time. Maintain alignment by watching the Ready LED. You should be able to make the gate width large enough for relatively large objects to pass through.

When using the DLS in Dark mode, use the procedures above to insure good alignment and optimal Sensitivity setting. Once you’ve determined where you want to place the Sensor and LED, you’ll need firm supports or clamps to make sure the components don’t move. One possibility is to mount them in a rigid framework made of PVC tubing such as the one shown in Figure 7. For this frame, three sections of 1/2-in tubing were used: 2 6-in sections and 1 12-in section. The interior holes for the emitter and detector are 13/64 inch in diameter, and the exterior holes are 1/4 inch. The separation between the emitter and detector can be changed simply by replacing the horizontal length of PVC with a different length.


Dark mode testing Photogate frame

Figure 6

Set up for testing Dark mode

Figure 7

Framework for photogate



The Light Mode
The Light mode is easier to use than the Dark mode, because the LED isn’t needed and precise alignment isn’t a concern. This mode is used to detect flashes of light or changes in intensity of light sources. One can, for example, use the Light mode to trigger on a flash of lightning. Follow the steps below to test the Light mode operation.

  1. Leave the Sensor connected but disconnect the LED. Note that while it won’t hurt to leave the LED connected, that’s one less cable to be in the way.
  2. Switch the Ready Mode switch to the Light position. Be sure to push the lever all the way past the center position. Turn the Sensitivity to 5.
  3. You’ll need a light source such as a flashlight or just the light from a smartphone for testing. Start with the room lights turned down and the light source turned away from the Sensor.  The Ready LED should be on.
  4. Now bring the light source toward the Sensor. At some point, the Ready LED will go dark, indicating that the light has been detected. Move the light source away to verify that the Ready LED turns on again.
  5. Try the above test with both high and low sensitivity settings. You should find that in an otherwise dark room, detection of the light source is fairly independent of the Sensitivity setting. If, however, you turn the Sensitivity below 1, detection may fail as it did in Dark mode.
  6. Turn the room lights on and repeat the tests from the previous steps. This time, expect to find that the light source isn’t detected at high Sensitivity settings. You’ll probably need to keep the Sensitivity below 5 when working in a lighted room.

The Shutter Output
In some situations, such as photographing lightning, you’ll need to trigger your camera shutter rather than a flash unit. Use the Shutter output for such situations. Like the flash output, the DLS immediately triggers the shutter output on reception of a trigger signal. Keep in mind, though, that the shutter itself takes time to actuate due to inherent shutter lag of the camera. The amount of the lag depends on the camera.

In order to trigger a camera, connect the shutter cable for your camera to the Shutter jack on the DLS. This requires a 3.5mm stereo plug on one end and the appropriate connector for the camera’s shutter port on the other. (See Figure 5.) Caution: Do not connect the camera to the Pulse jack, as this port will send a low-voltage pulse to the camera. See below for the use of the Pulse output.

3.5mm female - RCA male adapter
Note that the Shutter output can be used to discharge a flash unit rather than actuate a camera shutter. This provides a way to discharge two flash units simultaneously. When connecting to a flash unit, an adapter is needed to convert the RCA plug of the flash cable to a 3.5mm plug needed by the Shutter port. See the photo to the right. Click here for cable adapters.

Note about optoisolation: The Shutter port is optically-connected—as opposed to electrically-connected—to the DLS circuitry. Thus, the DLS cannot damage your camera. This, however, is not necessarily true if you use the Shutter port to discharge a flash unit. The voltage at the Shutter port can be no higher than 80 V in order to prevent the optoisolator from burning out; however, some legacy flash units have internal synch circuits with voltages up to 400 V. Such flash units may not be used. While modern units don’t have this problem, we don’t recommend using the Shutter port to trigger a flash unit if you’re not sure what the synch voltage of your flash unit is. If you want to check the synch voltage, there are videos on YouTube describing the process.

The Pulse Output
The Pulse port provides a low current pulse of about 9 V. This can be used to trigger flash units or other devices that require a low voltage pulse for triggering. Connection is made to the Pulse jack with a 3.5-mm mono plug. Note that the Pulse port will only power light loads and should never be used to power an inductive load. This may damage the DLS circuitry.


Connecting to a Delay Timer

One often wants to create a time delay between the trigger signal and the discharge of a flash unit or actuation of a camera shutter. In that case, a Delay Timer is needed. Simply connect a cable from the Flash output of the DLS to the Input of the Delay Timer. The cable needs to have an RCA jack on one end and a 3.5mm jack on the other. A cable with two RCA plugs could be used together with the adapter shown above.



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