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Assembly and Operating Instructions for Kits


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Assembly Instructions for an Amplified Sound Trigger



Front view

Side view

Here we show how to use a microphone and amplifier together with a silicon-controlled rectifier to build a very sensitive sound trigger with a wide-frequency response. We use the Radio Shack Mini-Amplifier (part no. 277-1008) shown to the left for its functionality and portability. The amplifier has 3.5mm (1/8") jacks for a microphone and an external speaker. An inexpensive dynamic microphone such as the one shown to the right (Radio Shack Recorder Microphone 33-306) will do. For convenience, a clip-on electret microphone can also be used.


When used as a sound trigger, a special cable is prepared that plugs into the external speaker jack. The other end of the cable can be connected directly to a flash unit, the delay unit on a breadboard, or to the external input on a Multi-Trigger enclosure, either the breadboard or PCB version.


The Mini-Amplifier is powered with a 9-V battery. The unit also has a jack for a 9-V AC/DC adapter; however, we haven't been able to find an adapter with the appropriate plug. Radio Shack says on their website to use AC Adapter 273-10027; however, a search on this part number turns up nothing new. A visit to a local store also yielded no results. We've tried our own 9-V adapter but, although the plug fits, the adapter doesn't provide power to the amplifier. Please contact us if you find an adapter that will work with the amplifier. We'll post the information here.


We provide the Output Cable Kit (OUTC) to connect the output of the amplifier to a flash unit. The Radio Shack Mini-Amplifier and Recorder Microphone are usually available at Search on the part numbers given previously.


The device can trigger on a normal, speaking voice or just by blowing past the microphone. It will even trigger on the sound of a drop of water hitting a solid surface, although it won't trigger on a drop falling into a pool of liquid. (In any case, for drops and splashes, we recommend that you use a photogate-delay combination.) If you find the trigger too sensitive, turn down the volume control on the Mini-Amplifier. You will probably find it more difficult to use the amplified sound trigger than our piezoelectric sound triggers SK2 and SK3. Unlike the latter triggers, the amplified sound trigger will trigger on most any sound in the vicinity of the microphone, so you have to be very quiet when using it. The click of the camera shutter may set off your flash prematurely.

Name product code Photo Quantity Function
Parts provided in the Output Cable Kit (OUTC)
TYN408 silicon-controlled rectifier (SCR) TYN408 1 The SCR act as an electronic switch. The amplifier output closes the switch which, in turn, triggers a flash or delay unit.
2-conductor cable   4 feet Used for the output cable

3.5mm male phone connector

(jacket may be gray or black)


1 This connects the output cable to the amplifier output jack.
Empty film canister   amplifier 1 OK, so it's just an empty film canister, but these things are becoming scarcer these days. The canister makes a handy protective container for the SCR after it's soldered to the cable.


RCA male connector



1 This connector is for the sound trigger output cord.
RCA female to 3.5mm mono male adapter 35mRCAf 1 This adapter is for connecting the sound trigger to the external input of a Multi-Trigger enclosure.
Coupler for two RCA plugs FFRCA 1 This coupler connects two cables with RCA plugs together (such as the sound trigger output cable and a PC cord).


Tools needed (not supplied)
Wire stripper
For soldering: 15-30 W soldering iron and solder, heat sink (a metal clip will do)


    Soldering Tips

    • Solder in a well-lit, well-ventilated, open area. Avoid contact with all metal surfaces on the iron.

    • Keep the tip of the soldering iron clean by wiping it against a wet sponge or towel before and after each use. A clean tip should look shiny and silvery; any yellow or black material on the tip will get into the solder and may weaken your solder joint.

    • Once the tip of your soldering iron is clean, touch a bit of solder to the tip just before use. This is called tinning, and helps the solder run more evenly.

    • Heat the connection to be soldered by holding the soldering iron to it, until solder applied at the junction between the two melts and flows freely. This ensures the connection and the solder are both hot enough to yield a good solder joint. This should take no more than 10-15 seconds. After the connection is heated, try to get solder along the entire length of the connection by briskly moving the solder and iron along.

    • Avoid touching only the solder to the connection, and then the soldering iron to the solder to melt it onto the connection. The connection will be cooler than the melted solder and won’t form a good solder joint.

    • Let new solder joints cool for several seconds before examining them. There should be solder all the way around the connection, forming a rigid joint. When done, unplug your soldering iron and let it cool.

Assembling the output cable


Click on the thumbnails below in order to view full-size images of the breadboard with the components that have been added in each step.


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Step 1: Stripping the cables


Begin by cutting the 2-conductor cable into a 1-foot section and a 3-foot section. Then strip the wires on one end of each section as shown to the left. Strip the gray insulation back about an inch and the red and black insulation about half an inch.

bb_065.jpg (87501 bytes)
bb_065.jpg (87501 bytes)

Step 2: Wrapping the black wires


Here's a description of the part that the SCR plays in the trigger. The SCR acts as an electronic switch. The microphone picks up a signal, the amplifier boosts the signal, and the boosted output signal from the amplifier to the gate of the SCR turns the SCR on. This closes the circuit between the anode and cathode and triggers the flash (or camera).


Now hold the SCR so that the legs are down and the writing is facing you as in the upper photo. This is the orientation assumed when referring to the legs as left and right. The left leg is the cathode, the middle leg is the anode, and the right leg is the gate.


Spread the legs of the SCR a bit to provide more space for wrapping wires. Now wrap both of the black wires around the left leg as shown in the lower photo.

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Step 3: Soldering the connection


In addition to the soldering tips given above, it's a good idea to use a heat sink when soldering semiconductor components like the SCR. The heat sink is just a small metal clamp that clips to the leg that you're soldering between the connection to be soldered and the body of the component. The heat sink shown in the upper photo was purchased from Radio Shack; however, any small metal clip will do. For that matter, the SCR's back plate serves as a heat sink as well, so you can get by without the clip as long as you don't heat the legs for a long period of time. Go ahead now and solder the wires to the left leg. The photo in Step 4 shows the soldered connection.


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Step 4: Connecting the red wires


Wrap the red conductor of the 1-foot cable around the right leg and the red conductor of the 3-foot cable around the middle leg. Then solder the connections.



bb_065.jpg (87501 bytes)
bb_065.jpg (87501 bytes)

Step 5: Encapsulating the SCR


It's important to secure the SCR so that it doesn't break off with repeated use. You could tape all the wires tightly or coat the legs in hot glue or epoxy resin. The method shown in the upper photo uses an empty film canister. First, drill or punch a hole about 5/16" in diameter in the bottom of the canister. Remove the lid and feed the two cables into the canister and through the hole. Before feeding the cable all the way in, tie a half knot in the cables. This will serve as a strain relief. If a pull is applied to the cables from the outside, the knot will feel the force rather than the SCR. Cinch up the knot close to the SCR and then push the knot and SCR gently into the film canister and snap the lid on.


The completed assembly is shown in the lower photo.

bb_065.jpg (87501 bytes)

bb_065.jpg (87501 bytes)

Step 6: Preparing to add the phone plug


Next, you'll work with the free end of the 1-foot cable. First slip the plastic jacket of the 3.5mm phone plug onto the cable as shown in the upper photo. Then strip back the gray insulation 1/4 inch. Strip back each of the red conductor about 1/8 inch and the black conductor about 3/16 inch.

bb_065.jpg (87501 bytes)
bb_065.jpg (87501 bytes)
bb_065.jpg (87501 bytes)

Step 7: Making connections to the phone plug


Slip the black wire through the longer lug of the phone plug and the red wire through the shorter lug as shown in the upper photo. Don't crimp the metal collar around the cable yet. If you do, the heat from soldering will melt the insulation and may create a short circuit.


Now solder the connections. Due to the large amount of metal in the plug, you'll find that it will take longer to heat up the lugs so that the solder will flow. The middle photo shows the soldered connections.


After soldering, clip off any loose wire strands. Then crimp the metal tabs around the gray cable as shown in the lower photo.

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Step 8: Reassemble the phone plug


Screw the plastic jacket onto the plug to complete the phone plug assembly. This is the end of the cable that will plug into the amplifier output. From now on, we'll call it the STC (sound trigger cable).

bb_065.jpg (87501 bytes)
bb_065.jpg (87501 bytes)

Step 9: Connecting the sound trigger to a flash unit or breadboard


The way that you prepare the free end of the STC depends on what you will connect it to. We'll first describe connections that are made with bare wires.


Connecting to a delay unit on a breadboard: In order to connect the sound trigger to the input of a delay unit on a breadboard, strip back the free end of the 3-foot cable as shown in the upper photo. You need only strip the red and black insulation an eighth of an inch for insertion in the breadboard. Then connect the black wire of the breadboard jumper to the negative (ground) column of the breadboard, and connect the red wire to the input of the delay unit. The input of the delay unit is 13F for the Multi-Trigger and 18F for trigger-delay combination circuits. The lower photo shows the sound trigger connected to the input of a delay unit on a breadboard. The delayed output is connected to a flash unit.


Connecting directly to a flash unit: You'll first need to have prepared either a PC cord or Flash-to-PC adapter that connects to your flash unit on one end and to the breadboard on the other. That cable--like the STC--will have bare red and black wires. You simply need to connect red-to-red and black-to-black. You could twist the wires together and tape them, but you'll need to strip back the wires on the sound trigger output cable further than if you were connecting to a breadboard. When connected in this way, the delay between the sound-producing event and the discharge of the flash unit is determined by how far the microphone is from the event.



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bb_065.jpg (87501 bytes)


bb_065.jpg (87501 bytes)


Step 10: Using the couplers


The sound trigger can be connected to the external trigger jack of a Multi-Trigger enclosure--either the breadboard or PCB version.--in order to use the delay unit of the MT2. This has the same effect as connecting the sound trigger to the input of the delay unit on a breadboard. In order to make the connection to the MT2, first solder the RCA male connector to the free end of the STC. The method is similar to what you did in Step 7. First slip the plastic jacket of the plug over the free end of the cable. Strip back the wires as you did in Step 7. Solder the red wire to the shorter lug and the black wire to the longer lug. Crimp the tabs onto the wire and screw on the jacket. The completed cable is shown in photo 1.


Since the external input jack of the MT2 uses a 3.5mm mono jack, you may be wondering why we had you solder an RCA plug rather than a 3.5mm mono plug to the STC. The reason is to avoid confusing the connectors on the two ends of the STC. This means, however, that you'll need an adapter to make the connection of the STC to the MTE. The appropriate adapter is shown in photo 2. The connection of the sound trigger to the MTE is shown in photo 3.


One other connection you may want to make is that of the sound trigger cable directly to your flash unit. You may have already prepared a flash trigger cable for use with the MT2 as in the photos below. In order to connect the RCA plug of the STC to the RCA plug of the flash trigger cable, use the RCA coupler shown below. (Click on the photo for a larger image.)


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PC cable prepared for use with MTE

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Flash-to-PC adapter prepared for use with MTE

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Use of RCA coupler


Note that connecting the sound trigger directly to a Camera Opto-Switch to trigger your camera will not work. You'll need to connect the sound trigger to the input of a delay unit and connect the camera to an output of the delay unit. A Camera Opto-Switch may also be required.

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bb_065.jpg (87501 bytes)

Step 11: Preparing a Quick-Connect Cable for a breadboard


If you prepared your cables as in Step 10 and also want to be able to make connections to a breadboard trigger circuit, you may be interested in the Quick-Connect Cable Kit. This kit includes parts for the breadboard jumper shown in the upper photo. Assembly instructions are here.


The lower photo shows the jumper cable connected to the delayed output of a Multi-Trigger.


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bb_065.jpg (87501 bytes)

Using the Amplified Sound Trigger


Connect a microphone to the amplifier INPUT jack and the sound trigger output cable (STC) to the EXT SPKR jack as shown in the upper photo. The microphone and STC are shown connected to the amplifier in the lower photo.


Connect the opposite end of the STC either to a flash unit, the input of a delay unit on a breadboard, or the external trigger input on an MT2 as described in steps 9 - 11. Turn on the volume control on the amplifier and dial it up to obtain the sensitivity that you wish. If the microphone that you're using has an on-off switch, turn that on. When you're finished using the trigger, be sure to turn off the amplifier in order to conserve battery life.






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