Stereo Digital Camera Power-up Pulse Generator

I find that powering up my twin digital Sony DSC-V1 cameras at exactly the same time frequently synchronizes the cameras to a remarkable degree, within milliseconds. The cameras are powered up by twinned Sony wired remotes by shorting the ACC port LANC signal conductor with the ACC port ground. With experimentation, I find further that the synchronization can be refined to within microseconds if the switch on-time (ACC port signal to ground short time) is reduced to a minimum, to the point where one of the cameras occassionally does not turn on. In addition, the cameras either power up in sync, or one camera does not power up, possibly relieving one of having to even check the sync.

From the reports of others wiring camera power switches together, I suspect that wiring up the power switch on each digital camera with this device would also provide a remarkable degree of synchronization, though I do not have a set of cameras to test.

The Circuit:

To test this possibility, I modified a standard LM555 timer "one-shot" circuit slightly to trigger on the down stroke of the trigger button, and to provide an adjustable pulse length centered around 80 msec. I built the circuit on a solderless breadboard, used a Sync Shepherd to show the degree of camera sync, and used a (poor man's) oscilliscope to measure the pulse length produced by this power sync circuit. The optoisolator provides complete separation of this device from the cameras, and of the cameras from each other. Here are diagrams of the schematic, and a printed circuit board pattern:

Parts List:

Part	Value	Digikey Number	Price	Description
R1-2	1M	1MEBK-ND	$0.28/5	1/8 Watt Carbon Film 5% Resistor
R3	51K	51KEBK-ND	$0.28/5
R4	50K	U262R503B-ND	$0.32	10 mm Trim potentiometer, horizontal
R5	150 ohms	150EBK-ND	$0.28/5
R6	510 ohms	510EBK-ND	$0.28/5
C1,C2,C5	0.1uF	P2053-ND	$0.39	Tantalum Capacitor Radial 2.5mm Lead Spacing
C3	1uF	478-1833-ND	$0.46	Tantalum Capacitor Radial 2.5mm Lead Spacing
C4	33uF	P2029-ND	$1.30	Tantalum Capacitor Radial 2.5mm Lead Spacing
Q1	5V	LM2931Z-5.0-ND	$0.86	5 volt regulator, TO-92, 0.3 volt drop out
IC1		LMC555CN-ND	$0.50	CMOS 555 Timer, 2-15V, 100mA sink/source
IC2		TLP621-2GRT-ND	$1.05	Dual photocoupler
D1	LED	P364-ND	$2.15/10	LED green diffused, lens 3mm diameter 5mm height
T4		2238K-ND	$0.49	9 volt battery clip
SW1,SW2		P10882S-ND	$0.36	PCB right angle push button, light touch 5mm 130gf

Construction Notes:

Attach power to the board in the right lower corner. The circuit runs at 5V, but the regulator needs at only 5.3 volts to regulate at 5v, so you can use a 6 volt or greater battery. I used a regular 9V battery for testing, but a smaller 6V camera battery, or an even smaller 12V garage door remote battery will work. The main power drain is the LED at about 15mA--the rest of the circuit when idle draws only 3.2mV. The optoisolator draws about 17mA, but only for the instant (~80 msec) the cameras are being powered up.

User Instructions:

If you have a pair of cameras with a LANC port (also called "ACC" on still cameras), you can use this device to power up the cameras through the LANC port. Get a couple of regular 2.5mm stereo plugs from your local Radio Shack (part 274-298), and wire up an extension for each connector from a set of paired wired remotes. This device then will briefly short the LANC signal lead with the ground lead, and power up the cameras. This device will only power up the cameras, and will not change the operation of the paired remotes.

If your cameras do not have a LANC port, the optoisolator serves as a switch for each camera. Attach wires from each camera's power switch to the terminals T1 and T2 with the common or ground at the negative terminal as indicated.

To power up the cameras together, first hold down button SW1 to turn on the device (D1 LED glows), then press button SW2 to send the power-up pulse, wait at least a tenth of a second, then release both buttons. By using a push button rather than a switch to turn on this device (LED glowing), the battery should last just about forever in spite of the small size of the battery. Turning R4 counterclockwise decreases the power-up pulse length, increases the likelyhood of synchronization, but makes it more likely a camera will not power up. Adjust R4 to a point where one camera or the other does not power-up about one or two in ten times. At this point, power-up sync should be optimal.

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