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Topic: Newbie guidance for dslr timelapse controller (use relay or transistor?) (Read 1 time) previous topic - next topic


I still haven't given up on this, my goal is to try and be completely confident in my understanding before trying it out...

I'm going with the transistor option.

I found this quite detailed and helpful tutorial and he is also using the same transistor as me which highlighted the calculations you were doing Nick:

I'm probably not understanding something here but could I for e.g. use my multimeter in amp mode - make the short with the multimeter - measure the current - then perform the calculations done in the video and by nick to select the best possible resistor for on the base?     Or could that be a bad idea considering I know nothing of the camera internal circuit?

Could someone also advise me about common grounding?  I find myself slightly puzzled between for example a battery with +/- terminals and my arduino with its GND pins.

Now the standard google response is its a common reference point for voltages..... but that doesn't really click in my head.

What is actually under the GND pins on the Arduino and why for example when I take my 5v to resistor to led and touch the other end to for e.g. a metal mic stand I get nothing.  What is under those GND pins that make the electricity flow but not when touching a mic stand on the actual ground?  (you may tell me this was a silly idea but I had to try)

This question is popping up because the camera has a battery with + and - and the arduino has +5v pins and GND and I'm just wanting some clarity on how the two layouts can mix.  How does GND pins interact with batteries, is the - on bat just a GND?

Again thanks for all the input and patience.  My understanding is growing and it will all click sooner or later!



Ground on the Arduino, is (connected to) the negative supply terminal, but only on the Arduino.  Any electrical circuit must have a complete loop in which the current can flow, so unless the "ground" on one device is actually connected to the "ground" on another, there is no path for current to flow back from one to the other.

Particularly in America with its two-pin plug system, appliances - such as your mic stand or a lamp fitting - do not have a connection to ground (and the mic stand as just a lump of metal is most unlikely to be connected to anything anyway).  The output from a "plug pack" (or a "wall wart") is just two connections with a voltage between the two, but not to anything else.  Computers - and therefore the USB connections - usually are grounded, but a bench power supply usually has three terminals - positive, negative and ground, with the option to connect the ground wire to either as the need arises.  A battery on its own has a positive and negative, but unless you connect one to the ground terminal of something else, there is no connection and certainly no "ground".  As a matter of practical convention ground is usually the negative - but only to the extent that you make it so.


Electrons flow the least resistive path...

If your Arduino GND and battery GND are not connected there is no path for the electrons to flow, it's all about the voltage differential between point A and B, the greater the differential the more current will flow, the Transistor when switched on via the base controls how much current flows between the Collector and Emitter, the more current greater the current flow.

But, no current will flow IF the grounds are not tied because there's no "path" or voltage differential for the electrons to flow.

Arduino Pin Out --- [1k] ---- Base Pin (of Transistor)

+ Collector (of your Camera)  (+ side of your button)
- Emitter (of your camera)   (- Side of your button)

When the transistor conducts, a path will be made and you can think of the + and - from the camera "making contact" like a push of a button.

Now, if there's no resistor your camera flash side (which i highly doubt) you could create a short... but don't worry because a "short" is what one would do everytime a button presses to trigger the flash on the camera, so there has to be a resistor there.

A relay could induce a high voltage and do something damaging to your camera.


Thanks guys,

Currently digesting your responses and will be having a good think about it..  I actually think I could put it together now by following things parrot fashion but am just taking my time to let it all sink in.

Will update the thread when I make some progress.


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