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Assembly and Operating Instructions for HiViz.com Kits

 

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Creating a Timeout Function for an Instant Output

 

Assembly instructions for other kits

 

When using a sound trigger with a particularly loud event such as a balloon burst in a small room, one sometimes gets an echo which can create multiple discharges of the flash for a single photo. This can also result when firing a gun, as both the sound of the gun firing and the bullet hitting a target can discharge the flash twice quickly in succession. So one obtains two images, slightly-displaced from the other, in the photo. In order to prevent such double exposures, you need a timeout function (also called reset delay) for the trigger. This deadens the trigger for a long enough time to prevent a second firing while the camera shutter is open.

 

When using a delay unit with the trigger, a timeout can be set for the delayed output. Instructions for doing this are provided with the various HiViz.com kits and products that include delay units. Consider, for example, the SK2-DU breadboard circuit below. (Click on the image for a larger version.) The resistor between 26C and 29C controls the amount of the timeout. For the 1 kΩ resistor shown in the photo, the timeout is only about a hundredth of a second. This kit and all of the HiViz.com breadboard kits with delay units are provided with an extra 100-kΩ resistor. Replace the 1-kΩ resistor with the extra 100kΩ resistor. This will produce a timeout of about 1 second and will eliminate double exposures.

 

sound trigger

 

For some situations in which the fastest possible response is needed for the trigger--for example, capturing a balloon burst--it's not advisable to set a delay. In such cases, one would use an instant output. In order to set a longer timeout for an instant output, simply dial up the coarse delay knob. This serves as the timeout for the instant output. Of course, if you're using both the instant and delayed outputs, the delay setting may be determined by other considerations. In that case, there are other methods to set a timeout for the instant output. These are described below.

 

Preparing a timeout cable

 

This method is the quickest to carry out. The disadvantage, though, is that it's dependent on the flash unit that one uses, and the method doesn't work with all flash units. See the Timeout Circuit method for a more universal way to achieve a timeout.

 

The addition of a capacitor of the appropriate value across the output of the trigger can have the effect of inactivating the trigger for a short period of timing after a flash discharge. The value of the capacitor depends on the make of the flash unit; also, this trick may not work for all flash units. For a Nikon SB800, a 2.2-μf capacitor works, but this same capacitor doesn't work with a Vivitar 283 flash unit. For the latter, use a 100-μf capacitor.

 

If you're using a sound trigger on a breadboard, the addition of a timeout capacitor is simple. Refer to the photo below. First, change the connection of the red wire of the flash trigger cable from 9A to 9C. Then connect the positive leg of the capacitor to 9A and the negative leg to the ground column.

 

trigger cable

 

If you're using an SK3 sound trigger, which is built in a project box, the easiest thing to do is add the capacitor to the flash trigger cable. Instructions for this are given below. This method also works if you have an MT-PCB2, MT-PCB3, or an MTE-PCB and are using the direct output of the sound trigger.

 

Click on the images for larger versions.

 

trigger cable Start with the trigger cable that connects the flash to the SK3 switch output.
cable with insulation removed Carefully cut away about an inch of of the gray insulation. Then cut away about a quarter-inch of insulation from each of the red and black wires.
cable with capacitor attached If you have a polar capacitor such as the one shown in the photo, note that one leg of the capacitor is longer. This is the positive leg. Take note of this leg. Now cut down the legs of the capacitor to about a quarter inch long. Then wrap the positive leg around the red wire and the negative leg around the black wire. Before soldering, you may want to test the cable with you sound trigger to make sure the timeout function is working. Connect the cable to your flash and trigger. Then tap the microphone twice in quick succession. If the timeout is working, the flash will discharge with the first tap but not with the second. After a brief time, tap the trigger again to see that it's functional once more. If the timeout function didn't work, first make sure you have the capacitor connected with the correct polarity. Try switching the legs. If that doesn't do it, try a capacitor with a different value.
soldering the legs of the capacitor Once you've verified that the timeout function works, you can solder the legs of the capacitor to the cable.
taping the cable Wrap electrical tape around the bare wires to keep them from touching each other and producing a short.

 

That completes the timeout cable. In case you have an application where you don't want the timeout, you could have a second trigger cable without a capacitor.

Timeout Circuit

 

Figure 1. Timeout circuit with fixed timeout interval of 1 second
Timeout circuit 1
Figure 2. Timeout circuit with continously variable timeout
Timeout circuit 2
Figure 3. Timeout circuit with low and high values of timeout
Timeout circuit 3

A timeout circuit uses a 555 timer to provide an output signal of variable duration. The instant output of a sound trigger or delay unit triggers the 555 timer on and initiates a square output pulse. As long as the pulse remains high, the 555 timer can't be triggered again, thus producing a timeout interval. The duration of the output pulse depends on the choice of the resistor and capacitor connected to pin 6 of the timer. In Figure 1 (click on the figure for a larger version), the values of C3 and R4 determine the duration of the timeout. The duration is calculated using the formula, Timeout in seconds = 1.1 (Value of C3 in microfarads)(Value of R4 in megohms). For Figure 1, the calculation gives Timeout = 1.1(10 µf)(0.1 MΩ) = 1.1 s, where the value of 100 kΩ is converted to units of MΩ using the power of ten conversion, 1 kΩ = 0.001 MΩ. The value of 1.1 s is approximate due to the tolerances in the values of resistance and capacitance. If, for example, each component has a tolerance of 10%, then the actual timeout could differ from 1.1 s by as much as 0.2 s.

 

If one wants the timeout to be adjustable, there are several ways to do this. For a continuously variable adjustment, see Figure 2. A 100 kΩ variable replaces the fixed resistor. A fixed 1 kΩ resistor placed in series with the variable resistor prevents the resistance from dropping to 0. This circuit provides timeouts from 0.01 to 1.1 s. The lower value of 0.01 s is less than the recycle time of a typical flash unit; therefore, such a low timeout appears to be 0 in practice.

 

A third method uses an SPDT switch to switch between two values of resistance. This is shown in Figure 3. The upper position of SW2 provides a timeout of 0.01 s while the lower provides a timeout of 1.1 s. A variation on this method is to use a fixed value of resistance, say 100 kΩ, and switch between two values of capacitance in place of C3. Values of 0.1 µf and 10 µf would produce the same timeout durations as the circuit of Figure 3.

 

One final note about the choice of the silicon-controlled resistor. The SCR needs to have a high voltage rating to accommodate flash units with high-voltage synch circuits. The EC103D SCR is a good choice.

 

 


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