any electronics boffins out there?

I would like to buy (or butcher) a light sensitive diode and adjustable micro timer to close a circuit and trigger my Camera.
I need to capture a falling object passing the slight sensor and delay closing the circuit until the object is in view (microseconds).
Can you suggest a component list? There's too much choice
I know I could just buy this, but the more 'home made' the better as I will be doing it with my 4 year old son - so lots of tinkering and soldering wires hopefully

Depends on how clever you want to be ...

In a logic circuit start with a 10 MHz clock (0.1 micro seconds)

Run the photo diode though an amplifier stage ito a latch, so that on triggering it will go to a FIXED state.

Use that to initiate a counter that ius running on the 10MHz clock.

The outputs of te counter will be binary, so use a set of micro switches to define te delay in 0.1 micro second increments. With those feeding a set of AND gates you can get a low to high (or high) to low transition) which you could capture using a latch (JK flip flop)and that could trigger the camera. The output would then also be fed back to the inputs to reset everything.

That is how you could do it ...

Hi Darkmunk,
The easiest way is to use an infrared diode, and a light sensitive diode the other end. A 555 timer should do the job for the delay (though really basic!).

I've seen plenty of projects out there for Veroboard... I'll see if I can dig up a web link

What's your electronics experience like?
Matt

Matt - that's the easy way ! At least mine would be a challenge and would be "programmable"

It probably wouldn't trip the shutter quick enough due to what is known as shutter lag. Flash in a darkened room would work, but might not be convenient.

shim

Try this:
http://courses.ncssm.edu/hsi/pacsci/fpaper.html

To be honest, unless you are actually breaking things , a simple NE555 timer would do the job nicely - you just twiddle the pot until you get a delay that works. It's more predictable triggering a remote flash in a darkened room than trying to trigger the camera

That said, it's still possible to trigger Pentax cameras through their 2.5mm remote control socket.

Polchraine - well, you could always hook everything up to a laptop and write loads of code... or stuff it all in a microcontroller Personally, I take Einstein's (IIRC) motto - "Things should be as simple as possible, but not any simpler"

Matt

Cool thanks guys.
I had the 555 in mind, and I was intending to trigger the shutter thru the 2.5 socket, but I can always trigger the flash if the shutter is too insensitive. I love the idea of getting all clever and hooking up a laptop (Vista notwithstanding ) but I think my boy might not be so impressed!
I haven't really got any experience of this but I find the theory and practice easy enough... it's the shopping that stops me in my tracks

Let me have a look at that link....

That link seems to be just the job Matt. thanks
As usual though it is American, so if you have any hot tips for sourcing these components please fire away


I was already looking at the ICM7555IPA from Maplins but my total lack of experience buying such stuff left me paralysed with indecision ('just a normal day at the shops then Mark...')

RS components ... http://uk.rs-online.com/

Farnell,

Maplin

or probably easier if you find someone locally who is into electronics - TV & radio repair shop, friend of a friend &c, or someone who works in the dockyard. The cost of that lot would be under £1 probably but buying from a one of the above would means 10 or 100 of each ... and will end up costing £25.


And good old SCRs for the outputs ... you will only need low power versions of those

I managed to pick up almost everything locally, but it's a bloody minefield! all the different permutations and the circuit I'm using is a bit old fashioned so I'm not totally sure the new versions I've bought are appropriate....
Anyway, my most pressing problem is the polarity of the capacitors, as I understand some get a bit teasy if they're the wrong way round. the black one below has what seems to be negative signs down one side, is this the negative pole?
I assume the yellow one doesn't matter?

Yes you are right - the black cap is polarised and if you get it the wrong way round you will end up with a bang and horrible smell!

so they are negative signs?
I have just realised that the black one has 63V written on it. Is this max volts? will it be ok as my .5 capacitor marked 'C' above?
Is this because the K10 and Metz flash are both low voltage?
I've got two CP106D thyristors (rated to 400v) is this OK?

You may have a problem - looking at the circuit, none of them should be polarised.

As for the Thyristors - you are only switching a low power part of the circuit in the flash or camera and get no where near the high voltage side so yes they will be fine.

As you say try it and see ...

I would also experiment with the output connected to a small bulb initially - rather than the camera/flash. Then when you are happy connect it fully.

Huh? Yes, the 10uF will be polarised. Shown in the diagram middle bottom. You'll see that one side connects to ground - make sure the "- - - -" side of the cap goes to the ground (shown on the left) and you'll be fine
And yes, marked as "63V" means that's its maximum safe working voltage.

Matt

I did say SHOULD be polarised ... that is that there is no need for any polarised caps. I agree it WILL be polarised which is different.