Making a controlable switch

[apburner]

I have a Rebel XTI that I wish to make an Intervalometer for with an 08M. Try as i might I cannot get a solid state relay (that I know works with a 120volt christmas light string and 5Volts as control input) to work. I think it requires a minimum voltage push on the out put lines to turn on. So I tried a 2n2222. Base to out4 and emitter and collector to the two sides of the switch input of the Rebel. It works but i so sensitive that just touching the base with my fingers makes the camera take a shot. I am very weak on analog circuitry and don't know how to make this work or am I going to have to go buy a reed relay. I guess I am asking if anyone has worked with a 5volt controllable switch other than a regular relay and if so is there a link to a schematic.
Thanks
Steve

 

[inglewoodpete]

Sounds like the 2N2222 is teetering on its switch-on point. Do you have a current limiting resistor between the PICAXE and the 2N2222 base?

 

[Dippy]

Sorry, I just re-read your post... as said by pete. For bipolar always FIT a resistor between o/p and base.

Do you know the circuit connection of the Rebel switch? It is quite important.
If no schematic is available then measure the voltage on the switch contacts relative to ground or battery negative (with the device powered up). Or, with camera OFF, measure resistance on switch terminals wrt -ve battery terminal.

If one side is 0v/Ground then transistor switching is perfect and a simple transistor switch, whether bipolar or FET, is ideal.

PS. I forgot to add that SSRs ahve an operating voltage range and AC ones are different to DC ones. Get the data sheet and have a read.
Also, out of interest measure the voltage across the Rebel's switch and note the polarity too.

 

[Tom2000]

The SSR's input circuit is a LED. So you can probably drive it directly from an 08M pin with a 330 ohm resistor in series.

It sounds like you have the wired remote circuit of your Rebel XT pretty well sorted out. If not, I have a diagram posted here.

(I also show how to apply a SSR -- a PAA110 MOS relay -- in the camera firing circuit.)

Good luck!

Tom

 

[apburner]

Well I got it to work. I think I had a cerebral flatulation. I think the wires were not in the proper orientation. Until I was asked to check the polarity of the rebel plug I never even thought of the fact that there had to be a voltage being monitored on the plug for a switch to work. Once I reversed the wires it worked the first time. i have got the output of the 8M going to the 2n2222 base directly no resister. And the two wires to the canon are hooked directly to the emitter and collector. Works great now to get it off the wireless bread board and onto a curcuit board and into a project box so I can pack it around with my camera. Thansk for all the help guys and I may try building something a little more sophisticated later with an LCD readout and field programmability. But this will work for now.
Steve

 

[inglewoodpete]

I don't kow exactly how you have this circuit wired but I'm worried about the risk of overloading something, particularly the camera's trigger circuit.

Without the series resistor between the PICAXE and the 2N2222 base, the PICAXE can dump over 20mA into the transistor. This can damage the PICAXE, transistor or MOST IMPORTANTLY the camera. My strong recommendation is to insert a 4.7k resistor between the PICAXE and the base of the 2N2222 to limit the current.

 

[Dippy]

apburner, just for a laugh, measure the current from PICAXE o/p pin to the transistor base.
It may only be surviving , without resistor, as you're just giving a short pulse to trigger the shutter(?)
One day you may do a time exposure....
Up to you though.