Radio controlled camera switch

[tony-ellis]

I have taken a single channel RC receiver from a simple rc car, which ran on 2 x 1.5v AA batteries. The output is red wire - pos, black wire - neg. These were originally connected to the motor causing the car to move forward. Press the transmitter and the polarity of the wires is reversed (red now becomes neg). This caused the car to go backwards.

I have connected the neg wire from the battery to a 5v reed relay and the black wire from the receiver to a common input on a bridge rectifier. I have connected the pos leg of the bridge rectifier to the relay. In the normal state, with neg going into the bridge rectifier, the relay is inactive. Press the transmitter, and the relay activiates, firing the camera. I have also linked a LED on the relay side of the bridge rectifier to indicate that the rc is operating ok.

My problem is that the relay will not function unless the batteries are absolutely fresh, and after a while in use the power drops. I thought of using a 9v pp3 battery but don't know how to regulate the voltage. An alternative would be perhaps to use a transistor, but I'm not sure how to connect it.

Any ideas.

Tony

 

[Nigel Goodwin]

You need a lower voltage relay, and NOT to use a bridge rectifier, use just a single diode - this has only half the voltage drop of a bridge.

 

[tony-ellis]

Thanks for the quick response!
I take your point re the lower voltage relay, but the 5v was the lowest I could find.
With regard to the diode, would a 1N4148 be adequate?
Tony

 

[Nigel Goodwin]

Thanks for the quick response!
I take your point re the lower voltage relay, but the 5v was the lowest I could find.
With regard to the diode, would a 1N4148 be adequate?
Tony

Depends on the current the relay needs, a 1A rectifer (like a 1N4001) would be better.

If you can't find a lower voltage relay you might wind your own coil around a reed.

 

[DirtyLude]

A transistor worked for my DRebel remote in a test rig. Actually right now I use a microcontroller to directly source the 'fire' pin and it works.

**broken link removed**

 

[tony-ellis]

Mark,
I was interested in your micro-processor, but it's too advanced for me. Would be interested in the transistor solution though.
My camera is a Canon EOS 20D, which has a different socket to your Rebel, but the connections are the same - Common, Focus & Shutter.
What transistor did you use, how did you connect them up with the transistor, and where could I link in a LED?

Tony

 

[DirtyLude]

Yes, I didn't mean for you to use the microcontroller, I was just showing off. I am fairly terrible at transistor theory, but I'll give you the basics of what you need to do. I'm sure someone who's more knowledgeable will currect me if I'm suggesting something wrong.

Okay, you have 3 wires. 1 wire is ground. When ground is connected to either the shutter or focus wires, they will 'fire' the shutter or do the focusing. You start by connecting the ground wire with the battery ground of your circuit.

To use the transistor: A NPN transistor like a 2n2222 will connect positive to negative through the collector to the emmitter when power is applied to the base. The emmitter will go to ground and the collector will be attached to the shutter wire. You don't want to apply too much current to the base, though, or you will burn out the transistor. Now, I'm not good at figuring out what resistors to use, so I usually start out with a 10k resistor and then go down until the transistor will 'turn on'. Usually 10k works fine for me.

So basicly you will have the ground wire from the camera go to the common ground of your circuit. You have three wires on the transistor, emmitter goes to ground, collector goes to the shutter wire from the camera, and when you apply positive power to the base through a resistor, it will one way connect the two and you'll get your shutter action.

You'll want to download the datasheet of whatever transistor you use.

 

[tony-ellis]

Hi guys,

Thanks for the info on the Transistors, which I will try. In the meantime, I've done away with the bridge rectifier, and replaced it with a diode. The system now works and I'm able to use the circuit to fire the camera from around 10 meters away. It's looking good. Thanks for your advice.
Tony