i'm building a flash trigger with arduino and a photoresistor and laser module.
working so far, but it's breadboard only.
so the distance sensor<->laser is only about 5cm.
now since i dont know yet what kind of photos i want to shoot and therefor not where to flash positioned, how far sensor/laser apart are etc, i'm having trouble attaching a cable.
if i'll solder it too short i'll have problem for some setups, if i solder it too long i'll have too much cable laying around.
anyway, so yesterday i was thinking. and got a brilliant idea.
USB.
why not solder three USB-A socket on the board and one USB-mini socket on each module (laser, sensor, flash hot shoe adapter).
that way the connection between the parts is flexible and cheap and expensional.
if i the things are near together i can use one of these retractable USB cables and have it all tidy.
if i need it to be few meter away, i simply plug some USB extension cables in.
best of all, the parts are cheap as hell.
a USB-A to USB-mini retractable costs $1.50
a 3 meter USB extension cable costs $3
and a USB connector is about 50ยข each
now the question, how long would it take for the signal to go throu e.g. 3 meters of cable? would the analog readout from the photoresistor be too slow for triggering? or do i worry too much and the delay is under a few ms?
i'm new to this whole thing so don't quote me but couldn't you have a switch based on how long the cable is? and us the according ms response time to trigger the camera/flash/etc?
well that of course.
i'll have a switch (actually its a potenti) which sets the delay between the detection and the trigger.
but if the delay is too long the object would already be on the ground (or whereever) when the singal is reported back.
so thats why i asked if the singal would take only a few (<10ms) milliseconds, or if the delay were too big to handle (like over half a second), though i dont think it would be a problem.
after all, network cables (RJ45) can be quite long and still maintain a high rate.
Correct, your biggest problem won't be with the length of your cable, at around a nanosecond a foot that won't effect much. However your use of a photoresistor may limit it as they are not the fastest optical device to respond to changes and time constant used will have the largest effect on how quick the whole process will be.
cable length doesn't affect the time to send/ receive a signal. what it changes is the resistance.USB devices don't work with a cable longer than 16 ft because of this. What happens then is you get standing waves which is when your signal bounces around inside the cable so you get " signal ghosts". It shouldn't be a problem though for just a trigger signal.
p.s an alternative to usb is Ethernet or plain old phone line cable. except for the initial cost of the crimper it is cheaper than usb if you want to make lots of cables.
so i was thinking, why not have the photoresistor and laser on the same board and just reflect the laserbeam with a mirror.
that way the resistor and laser would be right beside each other.
the distance flash<->board shouldn't be a problem, even if it would be 10 meters apart, since all the flash needs is a contact. and when i give it 5V and the cable "resists" too much it might be like 3V and even that is plenty to trigger the flash.
what to you think (i'm sure there is some mathematical formula for that), when i need at least 1V to trigger a flash how long can the USB cable be? (the arduino board provides 5V)
as i remember, for the formula i'd need the correct material, the diameter of the cable and the voltage.
but i dont know the dimeter of a USB cable ^^
but 15ft (~5m) should not be a problem to maintain the 1V, right?