I could go and do it all and may get it to work but would have no idea why a 2.2k resistor is the resistor of choice on the base why not a bigger one or smaller...
(5 - 0.7) / 2200 = 0.0019 A
(5 - 0.7) / 1000 = 0.0043 A
So you are letting around 2 mA flow, which is well within spec for the output pin.
Presumably that is enough to turn on the transistor (isn't it voltage that turns it on rather than current?).
Quote from: Nick Gammon on Oct 20, 2013, 12:40 amSo you are letting around 2 mA flow, which is well within spec for the output pin.OK, OK, I know it is well within spec. And I doubt whether the current matters anyway for a relatively short period of time. Just a matter of "no more than necessary". If we assume a beta of 100 - which should be really conservative, it can easily switch 200 mA. If it is switching logic levels in the camera as one would expect, that is immensely more than sufficient.Quote from: Nick Gammon on Oct 20, 2013, 12:40 amPresumably that is enough to turn on the transistor (isn't it voltage that turns it on rather than current?).Eh? Transistors ("transfer resistors") are current amplifiers. FETs switch on voltage.
Also have a look at http://www.martyncurrey.com/?p=34This is a simple guide on using an optocoupler to activate the camera shutter but it can also be used to fire flashes.
The fellow goes on about using isolation in case it "could kill your several hundred dollar camera", then proceeds to describe a circuit missing out on the resistor in series with the optocoupler LED.Give me strength!