Camera shutter switch signal

[FredericG]

I am working on an RC controlled trigger for my canon A70 camera. I intend to introduce a PIC between receiver and the shutter switch of the camera.

At the entry of the shutter switch I see a signal that is almost always high, but has small "glitches"; it is 10 ms high and 2 us low.

I was expecting such a signal, perhaps to multiplex the switch with other switches as done with keyboards. But only 2 us; the rise-time is almost 2 us... Why would they do that? :confused:

How would I interface to my PIC? In another project (where I have been interfacing with a room thermostat) I sampled the input signal with a PIC input in order to generate the correct output and simulate the switch. This worked but it was not 100% reliable. I ended up using an optocoupler to short-circuit all problems.

I am now wondering what I should do in this case...

Thanks,
Frederic

[Gary Warner]

I am working on an RC controlled trigger for my canon A70 camera. I intend to introduce a PIC between receiver and the shutter switch of the camera.

At the entry of the shutter switch I see a signal that is almost always high, but has small "glitches"; it is 10 ms high and 2 us low.

I was expecting such a signal, perhaps to multiplex the switch with other switches as done with keyboards. But only 2 us; the rise-time is almost 2 us... Why would they do that? :confused:

How would I interface to my PIC? In another project (where I have been interfacing with a room thermostat) I sampled the input signal with a PIC input in order to generate the correct output and simulate the switch. This worked but it was not 100% reliable. I ended up using an optocoupler to short-circuit all problems.

I am now wondering what I should do in this case...

Thanks,
Frederic
The pulse-train is likely part of a key scan, like you said. To use remote switching, use a FET circuit, a relay or other such isolated bi-directional switching on the output of the PIC. You can use an IC like the 4066 serise IC (quad bi-lateral switch) where one pin sets the I/O logic. That can be driven from the PIC. The smallest and cheapest option would be a switching FET circuit. A photo coupler circuit might also work well.

Is one side of the shutter switch ground or B+?

Gary
--

[FredericG]

I did some more research.

The switch has 4 pins, see numbers on the picture. Pressing the button halfway connects 1 to 2; pressing the button all the way down connects 1 to 3.

In idle, pin 1 seems to float while pins 2 and 3 are solid high (3.3v). Pin 1 seems to be an open collector that produces the spikes I talked about before on pins 2 and 3 when the button is pressed.

The good news is that, when I pull pin 3 down (constant), the camera just takes a picture and I do not see no side effects (like detecting other keys).
So it looks like I will not need any additional components :) , I hope I am not missing anything here :confused:

Thanks,
Frederic

[Gary Warner]

You're brave to pull that flex PCB out.

Can you get it back in? :p

Gary
--

[FredericG]

You're brave to pull that flex PCB out I didn't (and I am not that brave :D); it is a picture from this site: http://www.artecdesign.ee/~jan/Kaamerad/PowerShotA70/index.html

The shutter switch can be reached by removing just 3 screws. In a quest to find a decent place to connect a GND lead, however, I dismantled the camera in the stage of the attached picture. Without these pictures I wouldn't have had the nerve to take it apart that much...

Frederic

[Upup]

Any one offer some advice I am trying airial phots for the first time. I have sripped down a 1.3 mpix camera to 20 grms problem is powering it and keeping the weight down rewired it through a servo and micro switch worked fine but would like to get rid of on board batteries

The cam uses 3vts thinking of taking a lead from the rx but its 5 vts is there a simple way to step it down ie resistor if so which one?

The cam in the photo is from michelle.bromehead@tiscali.co.ukthey are so helpfull I lossed instructions and they sent new by return post They have got several types of cams.

[FredericG]

Upup,

It will not be as simple as inserting a resistor. It COULD be as simple as inserting a linear regulator like an LM317 or LM1117.

BUT, when sourcing the current from the receiver, you could overload the BEC of the ESC. You need to know how much current your camera will require. See this thread: http://www.rcgroups.com/forums/showthread.php?t=441154

Frederic

[Upup]

Fredricg........ thanks for that I will have a look in MAPLINS to see if they have any

[Upup]

Fredricg this lm 317 will it drop voltage from 11.4 in to 3 vts in which case i can tap off before the esc directly off the battery.

An alernative did come up -- to take the 5 vts from the rx side and feed it via the usb port on the cam.

I think the LM option (above) is more elegant as it overcomes the problem you raised with the bec not being able to cope.

Excuse my ignorence in matters electronic, I am just gropping in the dark and tend to look for mechanical solutions.

Using the USB method keeps the auw to 1.5 oz how dose that compare to other setups??

[Upup]

Help! I have and purchased Lm 317, m240r resistor and wr41 pot as advised in the shop (wish i knew what i was doing) need to drop 11.4 v to 3 v (see above).

Guy in Maplins ( uk's radio shack) said I will draw u a diagram confused himself, then me, then gave up "the manager is watching and I cant spend time with customers"

Any help me with a sketch digaram for assembly

[FredericG]

wish i knew what i was doing hmmm...
If I where you I would try to feed via usb from the receiver. Do a test on the ground by constantly moving the servo’s while taking pictures during 15 minutes. If you do not loose control, you will probabey get away with it…





You need to have a look at the datasheet of the LM317, http://www.fairchildsemi.com/ds/LM/LM317.pdf, look at “typical application” on page 3. You will also need 2 caps...

That you can feed it with 5v is new information. This provides the option to feed the camera from the receiver directly. I have done that before with a PenCam. Will you overload the BEC? This depends on the ESC, the voltage of the flightpack, the servo’s and the amount of current your camera needs.

Feeding it with 5v (on usb) would also be a better solution when you would decide to feed it over the regulator (lm317) because the camera will probably consume less current and the voltage drop over the regulator is smaller. Both contribute in less energy dissipated by the regulator. If you do not understand this, let me know, I can elaborate.

However, it is not sure that the camera will take its power from the usb. Possibly it will only draw current after communicating with the usb master (PC). But it might work.

Hope this helps,
Frederic

[Upup]

FredericG....... Thanks for the guidance , the link is a help, I think I understand ( a bit) I have been doing a little web research it talked of heat dissipation regarding the lm 317.
There was an idea of using a switched regulator something about packaging the power making it much more efficient.
The guy in the shop lossed his way completly rolling rapidly downhill from " I will show you how it's easy" to a realy embarased state , felt a bit sorry for him to the point that I wish I hadn't asked.
The Usb route works ok I tested it before buying the Lm, the cam @ 3 vts is designed to double as a web cam @ (5vts), the only thing that I will have to be careful of is keeping the cam powered ( if it loses power completely you lose photos). Just need to be certain to reconnect a power pack before removing the cam from model.

I still prefer the idea of taking power directly from the battery,( the feed being 11.4 v li po) if using the usb connection via the rx and the bec cuts the power I will lose all the photos.

Any thoughts ?

Regards Jeff

[Bearded Flyer]

Jeff,

I would have thought that I the BEC cuts the power (therefore no receiver power and no servos) then the photos would be the least of your worries :eek:

Seriously I used a LM317 to power my Aiptek 2Mega SD camera at 3v from a 7-cell NiMh pack. It worked well but the regulator can get hot so it is best to locate it outside the plane in fresh air. You can get heat sinks for them but it should not be necessary.

Richard

[JimDrew]

Put a large size (1 watt) resistor in between the power source and the LM317. This reduces the current to the LM317, allowing it to run cooler. You will need to determine the amount of current required for your application, and don't forget to include whatever quiescent current is used by the LM317 itself and some additional overhead. If you needed 200ma of current total, and your input voltage is 12.6v (3S fully charged), then your series resistor would need to be 63 ohms. As the battery voltage drops, so does your current, so try to factor in everything when selecting the resistor.

[Comatose]

http://www.dimensionengineering.com/DE-SWADJ.htm would be more efficient, easier and run MUCH cooler than any 317 based solution. Its a self-contained switching regulator thats designed as a linear regulator replacement.

Sorry for the shameless self-promotion, but its the right solution here.

[FredericG]

When the BEC shuts down, you will not only loose your pictures but also control over your plane.

When you feed at the USB, you will put less stress on the LM317, and I suppose it will be much safer for the camera too.

You can insert a resistor between battery and LM317 to eat some of the TENSION. Suppose your camera uses 100mA and your battery 10V. With a 20 ohm resistor, there will be a drop of 2V over it. So the LM317 will still have to convert from 8V (instead of 10V) to 5V. But suppose your camera uses 500mA while taking a picture. The drop over the resistor will be 10V (0.5A x 20 Ohm), so no more power for the LM317... So it you insert a resistor, you need to know exactly what the max current is your cam requires, even small spikes. For that you need a scope.

The switching regulator is a much nicer solution. But I would buy it (from Comatose for example ;) ), not try to build one.

Frederic

[JimDrew]

A series resistor drops current, not the voltage. E=I*R. So, for 10v power source providing a current of 100ma (.1 amp), the equation is R=E/I, which is 10v/.1amp = 100ohms.

The best solution is definitely the tiny switching supply!

[FredericG]

I suppose we are talking about different things here.

How I see it:
The camera needs 5V and it will take some current. It dictates the current it takes and that current fluctuates.
The LM will cause a voltage drop that is independent of the current taken by the camera. The resistor causes a voltage drop that depends on the current.

Frederic

[Dan Baldwin]

I suppose we are talking about different things here.

How I see it:
The camera needs 5V and it will take some current. It dictates the current it takes and that current fluctuates.
The LM will cause a voltage drop that is independent of the current taken by the camera. The resistor causes a voltage drop that depends on the current.

Frederic

Fredric, you have it exactly right. An LM317 should work very well if you have a source voltage of 10 volts, and an output voltage of 5 volts, and the maximum current is less than 1.5 amps. The only problem with a 317, or any linear regulator is that half of the power will be converted to heat. If the current draw is 100 ma at idle, that would mean that the heat generated would be .5 watt (.1 amps x 5 volts dropped across the regulator). .5 watts is not difficult to deal with. You would need a fairly small heat sink on the 317, preferably placed in the airsteam. If the camera takes more power while it's taking a shot, it shouldn't make that much difference in the amount of heat generated by the regulator since it will be for a very short period of time. In my opinion, a linear regulator with a heat sink would be simpler and much cheaper than a switching regulator. I am always concerned about noise when a switching regulator is put on an RC aircraft. I'm not familiar with Comatose's regulators. It could be that they are specifically designed for RC use and don't produce any harmful noise.

Dan

[Tomapowa]

Comatose,
Does your (i.e. Dim. Engr) switching regulators use shielded inductors ?
Also, what is the switching frequency on these regs?

[Comatose]

Comatose,
Does your (i.e. Dim. Engr) switching regulators use shielded inductors ?
Also, what is the switching frequency on these regs?


Yes, shielded inductor, and they switch at 260 khz. Its the same switching core as in our parkBEC. Interference won't be a problem.

[FredericG]

Comatose,
Are here distributors in Europe?

Frederic

[Comatose]

Comatose,
Are here distributors in Europe?

Frederic

http://www.robot-italy.com/product_info.php/cPath/6_35/products_id/530

We also are happy to ship them directly to europe, and shipping is only $1 anywhere in the world for them. Either way.

[Upup]

Thanks for all the infomation it seems that the switching reg in the way to go.

[Upup]

Just an enquiry what do these regs weigh

[Zlatko]

Just an enquiry what do these regs weigh

Have a look at the link Comatose posted earlier ( 5.5gm ).

I'd also like to add that I got some products from Comatose and they got to AUSTRALIA within 3-4 days !!! :) So, Europe shouldn't be a problem.

Also, they all work great, from the switching regulators, to the adjustable ones to the accelerometers ;)

Cheers

Edit: If you just need 3.3 or 5 Volts step down than have a look at the Fixed Switching regulators, they are about 3.8gm.
http://www.dimensionengineering.com/DE-SW0XX.htm

[FredericG]

I ordered from Dimension 7 days ago. An hour later I got a mail that my order was shipped and today I received it. :) I am impressed

Thanks
Frederic