Digital Camera Becomes Video Transmitter


In the arena of high altitude balloons, Canon’s PowerShot series of digicams are the camera du jour for sending high into the stratosphere. There’s a particular reason for this: these cameras can run the very capable CHDK firmware that turns a $100 digicam into a camera with a built-in intervalometer along with a whole bunch of really cool features. It appears this CHDK firmware is much more powerful than we imagined, because [Chris] is now transmitting pictures taken from a Canon a530 to the ground, using only the CHDK firmware and a cheap radio module.

These PowerShot cameras have an ARM processor inside that runs VxWorks, a minimal but very capable OS for embedded devices and Mars rovers. By tying in to the Tx and Rx lines of the camera, [Chris] can issue commands to the OS, change settings, and even install his own code.

With the help of [Phil Heron]’s SSDV encoder written in C, [Chris] was able to get the camera to transmit images  with a small radio transmitter that fits in the battery compartment. Right now, [Chris] has only built the CHDK + SSDV for the Canon a530, but with how useful this build is, we expect to see an improved version very shortly.

21 thoughts on “Digital Camera Becomes Video Transmitter

    1. I think it’s an issue of support. If you put a feature in a product, you need to test it, you need to write up instructions in the manual. You have to teach your tech support people how to field questions about it. I think Canon is taking just the right approach by allowing people to update the firmware and add their own features, this way they can make lots of people happy with little effort on their part.

  1. i love the design and i love the way he fit it all in but i have to ask … why was it necessary to put the batteries on the outside and the components on the inside instead of just leaving the batteries in and putting the xmitter on the outside?

  2. I’ve had this very camera since 2006 & was increasingly close to pensioning it off due to it’s battery drain (2 x AA ) & pickiness on supply voltage. 2 x 1.2V NiMH just didn’t cut the mustard with it… However it’s had a wonderfully new lease of life since I simply fitted a single 700mAh 3.2V LIFePO4 AA 14500 rechargeable cell,costing US$3, along with a place holding straight thru’ dummy. SAee a similar apparoch =>

    These cheap LiFePO4 cells retain an extremely flat discharge until near exhausted, yet are quite tolerant of on the fly charging (that may come from a solar panel when aloft)..It strikes me hence the author may care to do the same?

    1. However, if you try to charge the cell with the camera, you risk a fire because NiMH chargers are designed to trickle charge once full, which causes lithium batteries to overcharge and burst.

      A shunt circuit could be made that monitors the cell voltage and triggers a bypass resistor once the cell reaches 4.0 volts. That would probably also trick the NiMH charger to think a voltage delta event has happened, because NiMH batteries change their resistance when full, which signals a smart charger that the battery is done.

    2. Dax: LiFePO4 battery CV charging voltage is 3.6V. You could use a LDO
      set to 3.6V in series or use a proper LiFe charger chip.

      Manuka: Yeah. I use LiFePO battery with my (old) Fujifilm camera that
      seems to run into a lot of issues with NiMH as I found out that its
      undervoltage detection at 2.5V (drift?). I am very happy with these
      batteries for my camera. I have a NiMH that was dead shorted and it
      makes a good dummy cell.

  3. I’ve grown fond of the nickle-zinc rechargeables.
    They have a higher OCV when fresh charged.
    BUT you have to watch out for the “knee voltage” curve being in a new place.

    None of my cameras are calibrated for this
    and the camera will not know that the cells
    are about to go over the cliff
    and shut the camera down.
    ….. corrupt or lost files are no fun :(

    So you have to keep a close eye
    on the battery indicator.
    as the mid point bar is actually the low reading now.
    The upside is better performance while the cells are fresh.
    better flash recovery and slightly faster auto-focus.

    downside: My Panasonic looses it’s auto-focus
    first, when the cells are low.

    They’re also handy for making cheap flashlights brighter too.
    But I don’t know how much it affects the longevity of them though.

      1. Yea, I’ve decoded SSDV data from flights over 500km away, once they get to a high enough altitude to get over the horizon. It still amazes me that I can hear a 10mw transmitter that distance away, let alone decode images transmitted with it. The record for decoding telemetry from one of these modules is 800km!

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