Building a
Digital Intervalometer

Having used a single frame advance Super-8 and a couple of Sony Hi-8 video cameras to do some time lapse work over the years, Minolta's implementation of an intervalometer has left a lot to be desired in the Dimage cameras.

Wanting to do a documentary on the removal of a historic Railroad Bridge, I'd planned to shoot DV of the details and also time lapse with a 'still' camera, my upgraded Minolta Dimage 7.

The reasoning behind this choice is the excessive wear noted on the camcorder's tape transport when using it as a single frame grabber. Most consumer units aren't built for this type of heavy usage. As my Minolta has the IBM 1 GB Microdrive, it'll easily handle the number of images required.

Unfortunately with Minolta's allowed choices of 99 frames and a 1 minute minimum interval (their 'time lapse') -or- the UHS mode of 5 frames per second, but only a maximum of 80 images - this just wouldn't work for a two day project! One's too slow, the other too fast - and neither allows the length of time needed.

As Minolta does have a remote control using a simple contact system, with the camera providing the switch 'bounce' buffering, it becomes easy to trigger the camera through the modified remote (RC-1000).

Other digital cameras with remotes or triggering inputs can also be fitted to this little circuit. As the design is a 'dry' contact type - this shouldn't cause any 'warranty' problems. No voltage leaves this device, thanks to the relay's isolation.
 



WARNING

This circuit, its design and all information contained herein,
is provided AS-IS.
 
If you choose to build it, you assume all responsibility,
both for your work and any problems or damages
use of this idea may 'cause'.


 

Circuit Description:

The LM-555 timer IC is easily configured to output a pulse after an interval determined by a simple RC combination. By using a dip switch to short out selected resistive components, the timing can be changed in a binary additive fashion.

To allow settling of the circuit and ensure that the output relay has relaxed, a minimum time was set at 2 seconds. The clock is then adjustable from 2 seconds (all switches 'ON") to 65 seconds (all switches "OFF"). The resistors are chosen in a 1, 2, 4, 8, 16, 32 ratio with approximately 14.7 K ohms giving a 1 second time. This will vary slightly with the actual value of the nominal 100 uf capacitor used.

A second 555 circuit is used as a 'one-shot' to pull in the output relay and set its "ON' time. This is necessary as the camera requires a held contact for approximately 0.25 seconds. Adjustment of this is easily done by selecting the RC constant of the 100K resistor and 4.7 uf capacitor.

For ease of construction the LM-556, a dual 555 device, was used. To keep the current drain low and not require a driving Q for the relay, a fairly sensitive 5v relay must be chosen.

Building the circuit:

The circuit was laid out using a method I'd adopted for 'one-off' projects while working in the broadcasting industry. For lack of a better name - I've often referred to it as a "component lead PCB". The idea is to lay out the project in a manner that can be quickly translated to a real PCB if it needs replicating or can be used by others.

I chose a 'dual compartment' case for the project as I wanted to easily access the timing, power and "start/stop" switches. Placing those parts where the 9v battery would normally go keeps the rest of the circuit enclosed. Pop the 'battery' lid, make the settings, turn on and snap closed.

The 'Power' jack (an "M" 'short' type), the confidence LED and the 1/8th inch Mini Phone jack are all on the case's removable panel. I used heavier wiring and some epoxy to join the circuit card to this panel via the bodies of those components.

The rest of the wiring, except for three jumpers, is all on the underside of the card, as in true PC wiring.

The shaded area on the component side of the board (top image) shows where the internal barrier of the case rests. Slight notches were cut to clear the three jumpers. It then holds the card firmly in place.

Operation:

Preset the dip switches for the desired time. The ON position shorts the series resistor associated with that switch, shortening the RC constant and the firing interval.

Turn OFF to add the times shown:
Switch 1 =   1 second
Switch 2 =   2 seconds
Switch 3 =   4 seconds
Switch 4 =   8 seconds
Switch 5 = 16 seconds
Switch 6 = 32 seconds

Remember to ADD the minimum 2 seconds to all selected timings.

Switches 7 and 8 are in parallel and either will apply power from the regulator to the IC and timing circuits. ON is "on".

The large SPST enables the output to the relay, LED and subsequently fires the camera. As the circuit fires immediately on power up, and again upon removing power, I chose to interrupt the output to better control the number of images.

The brightness of the LED can be trimmed by adjusting the resistor in series. I've used a fairly dim setting with the 2.7K resistor. A 1K would work well for more visibility. The voltage applied is about 5.8 v. It depends upon the draw of the relay chosen.

With the use of the full bridge rectifier and LM-7808 regulator, I can power this from a 9 - 15 v. battery (including the auto accessory power), as well as 8 - 12 v AC or 9 to 15v DC wall worts.

 



WARNING

This circuit, its design and all information contained herein,
is provided AS-IS.
 
If you choose to build it, you assume all responsibility,
both for your work and any problems or damages
use of this idea may 'cause'.


 

The contacts on the Minolta's RC1000 socket are used as follows:
Right side of camera is the "Take".
Middle contact is the "Focus and Exposure" pre-set.
Innermost contact is the "Common".

As I use the camera in a manual focus and exposure mode for time lapse, only the outer two contacts are closed by my intervalometer..

 

My Working Drawings
 
 

 

TTRR IconTonopah & Tidewater Railroad

12/08/2002