Making an electronic cable release for use with

 DSLR's 

For any camera that uses the standard 2.5mm stereo audio connection for it's electronic cable release

[ Canon 300D/350D/400D. Pentax *ist-D/Ds/DL/K100D/K110D/K200D etc]

When we started this site one of our first pages concerned the conversion of the Pentax cable 'F' switch - used with the 'Z' series film cameras -  to enable it to be used with the *ist-D. Cable 'F' switch . (This can also be used when converted with the same cameras that this DIY electronic cable release is intended to be used with). Since that time there have been several users who have made their own electronic cable releases and recently there has been renewed interest in this subject.

In order to assist those who would like to try this we are providing some details on how to go about this and the parts that you will need. Making your own electronic cable release is fairly easy and cheap. It cost us just £5.00 to buy the parts needed, a fifth of the cost of the cheapest electronic cable release that uses the same connection.

The electronic connection used in the camera's is a  2.5mm stereo audio socket. Many DSLR's/SLR's from several makers now use this connection for use with electronic cable releases. Plugs to suit this connection, usually called stereo jacks, are easily obtained from any good electronic store, as are most other parts needed. In the UK  www.maplin.co.uk  is a good online source. They have also recently started to open stores on a number of high streets, conveniently replacing the Tandy electronic shops, a past good source of components, who disappeared a few years ago.

As there many camera users who are uncertain about how the electronic cable releases work, and thus what parts are required, and why,  we will deal with this aspect first.

Camera Shutter Buttons

Camera shutter releases - shutter buttons - work in two stages. The first stage, the half-press, engages the AF and metering circuits. The second stage, the full press, also engages the shutter circuit. The switches used are of the pressure type. Applying pressure makes/completes the circuit, removing it breaks it. These are signal circuits. What this means is that the circuit does not carry much current, just that when made it 'switches on' further circuits. In these cases the AF/metering and shutter circuits.

Electronic cable releases are designed to work in the same way, again using two stage pressure switches. In order to make them easy to use with the bulb mode, especially with long timed exposures where it can become awkward continuously holding down the shutter button, some cable releases have a 'lock' which when used keeps the switch 'on' and the shutter open. In bulb mode of course the shutter remains open for as long as the shutter button is pressed down.

Two stage switches are used to ensure the AF/metering circuits engage before the shutter circuit. This is for two reasons. It enables the AF system and metering to be used without actually taking a shot, the button only being pressed half way and no further. And it prevents the shutter being fired without the lens being correctly focused if this is desired.  Whilst the shutter will fire if the circuit is energized, the circuits are designed so that once the AF circuit is made, the shutter circuit will not complete and the shutter fire until the AF system has worked and confirmed correct focus. This only occurs in single shot or continuous AF. When the camera is set to MF mode, whilst a half press of the shutter button will engage focus confirmation and metering, it will not prevent the shutter firing on full depression of the shutter button, which occurs irrespective of whether correct focus has been obtained and confirmed. 

In single shot AF once the shutter button as been pressed halfway and the circuit made the AF works until focus is confirmed. It does not matter if the circuit remains made the AF will not continue to work. The circuit needs to be broken and re-made for this to happen. This happens by lifting your finger from the shutter button and then pressing down again. In continuous AF the opposite happens. The AF works and continues to work, re-focusing as necessary, until the circuit is broken.

When the shutter button is pressed fully down and the shutter circuit is made the shutter fires. For how long it remains open depends on the metering mode used. In every mode except 'bulb' the time is fixed by the metering method being used and the shutter will close after this time. In 'bulb' mode the shutter remains open for as long as the shutter button remains pressed down. How many times the shutter fires depends on the AF mode chosen, one in single shot and multiple in continuous.

As you can see, shutter buttons using pressure switches are used because they provide the most convenient way of making the AF/metering work and firing the shutter. The only slight drawback with the design is, as we have stated, the awkwardness of holding down the shutter button for long periods in connection with long time exposures in bulb mode. But this is over-ridden by the fact that in general very few photographers use bulb mode much these days, and some not at all. This is particularly true of present day cameras where timed exposures of up to 30 seconds are common and cater for most needs.

Wiring circuits

The circuits for wiring a cable release are simple on/off one's, most of the circuitry being inside the camera. Just three core cable is needed. One core carries the 'feed' from the camera to the switches, with the other two carrying the feed back when the contacts are made completing each respective circuit. fig 1

Although we have tried, we have been unable to find any proprietary two stage pressure switches that could be used as a shutter button, and so two individual push button pressure switches need to be used. These are very common and easily obtained. As a result all you really need to make a cable release are two push button switches, a container which fits in the hand in which to fit them, a length of three core cable, and a 2.5mm stereo audio jack.

Finding a container in which to fit the switches, and which is easy to hold and obtain has been cleverly solved by those who have hit upon the idea of using an old film canister/container. Small diameter 3 core cable is not so easy to find. We have used some 3amp, but it's diameter is still a bit too big and the cable is rather stiffer than we would have liked, but it does the job. You may have better luck in finding more flexible smaller diameter cable.

An additional switch you may like to incorporate into the design is a simple on/off type to use with the bulb mode. This is wired in parallel with the shutter circuit push button and used instead of it when needed. fig 2

Here are shots of the switches used along with the stereo jack. 

The wiring for the stereo jack is as follows ; Base - feed. Middle - AF/Metering. End - Shutter. Be sure to use a simple on/off type toggle switch if you fit one for the bulb mode. These toggle switches are made in a variety of formats which outwardly look similar, single pole, double pole, on/off, changeover, centre off, passing contact. Just ask for a single pole on/off type.

Actually making the cable release is not a difficult or time consuming business and is easily accomplished with a small soldering iron of about 15watts with a small tip and something with which to make the holes in the film canister for the switches and the wire.

We played around with the film canister for a while whilst deciding where to position the push buttons and came to the conclusion that for us, placing the AF button in the middle top, and the shutter button about half way down the side worked well. It seemed easier to push down with your thumb, and then squeeze with your index finger, rather than the other way around. But of course where you place the buttons is up to you.  Some place both buttons on the side. As two individual buttons are used you must remember that the design requires that you are able to depress the AF/metering button before the shutter one. All you must remember to do is to leave enough room between them inside the canister so that their respective contacts do not touch.

It is best to actually wire up the two push button switches before fixing them in place in the canister. It's impossible to solder up the connections once they are fitted in the canister. Similarly it's best if you can find some way of holding the stereo jack while you are soldering up the wires to it. We used one of those 'helping hands' units that has crocodile clips for holding objects while you work on them. See photo's below.

And here is the finished result next to the standard Pentax cable 'F' switch. As you can see there is hardly any difference in size and it works just as well. 

Not bad for a fiver [£5.00], a little effort finding the parts, and an hours work making it.