This is how simple it is.

There are many types of sound trigger devices available for triggering cameras. Most of them are rather expensive and they have many other features. For some applications the variable delays and many features are not required. Here is a very simple way to create a sound trigger using just two components: A transistor and a diode.

First a little background: This unit is used to trigger a Nikon D700 but I expect that the same circuit will work with most cameras.
Before starting the design I measured the shutter delay of the camera with a remote switch trigger. The shutter delay was 35 +/-2ms which is slightly better than Nikon's 40ms specification.
To acoustically trigger we need to pick up the sound using a microphone, amplify the electronic signal, and then rectify it to activate a switch that will trigger the camera.
Almost any type of microphone and audio amplifier that produces at lest one Volt output can be used. Just verify that there is no DC voltage on the output of the amplifier before connecting the circuit. (Normally amplifiers have an output capacitor to isolate the DC component.) If not, a 1 µF capacitor can be added between the audio amplifier and this circuit.

A very convenient and self-contained option is to use a Sound Pressure Level (SPL) meter. An old low-cost Radio-Shack 33-2050 meter was used for testing. They sell on eBay for $25 or less.

SPL Meter

Instead of showing a circuit diagram I temporarily connected the components as a visual design.

The Connections

This just shows the basic connections of the wires and the diode to the transistor. For the final assembly it can be much smaller

Only two items are required besides and wires and connectors:
1. A transistor, type NPN, for example 2N3904.
2. A diode, for example 1N914.

The components are very non-critical. Almost any NPN transistor will work and any diode will be fine too.

The black wires are "Ground" (common), the red one is audio input and the yellow trigger output.

The easy, but expensive, way ($45) is to buy a Nikon MC-22A. The color coded banana plugs can be seen in the first photo.

MC-22A

The low-cost way is to buy an aftermarket remote trigger (about $5) and cut off the switch and just use the connector and cable. In that case you need to use an Ohm meter to find the correct wires since the color coding is unknown.

Brand X

For camera pinout information see: www.vinland.com/Nikon_10-Pin.html

The camera should be set to manual focusing and the "awake" time "C2" should be changed to a much longer value depending on the application.

The two components can be hidden in any very small non-conducting box. They can even be left in the cable joint and covered by electrical tape.

I wanted a very small device so I hid the components inside the Phono plug.

The parts are really squashed together

Finished and closed

The space is really too small inside the connector so it is difficult to make it fit. If I have to make another one I will use surface mount components which would easily fit.

This circuit works fine on my system but any time non-brand name equipment is used there is always a possibility for errors or damages. In summary, use this information at your own risk.

For more camera information and other projects see:
www.vinland.com/_Misc.html

Bertho Boman
Vinland Corporation
11600 NW 20^th Street
Fort Lauderdale
FL 33323
(954) 475-9093
Email: boman33 at vinland dot com
www.vinland.com