Electronics > Projects, Designs, and Technical Stuff

Hacking a remote for a small digital recorder

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drm1:
Can anyone help make some informed guesses about a remote control for a portable digital recorder? I want to hack a wireless version and need to know how it works.

The recorder is a Zoom H4N (http://www.sweetwater.com/store/detail/H4N), which has a 1/8"=3.5mm jack for a remote. The wired remote (http://www.sweetwater.com/store/detail/RC4) made by the manufacterer has a 4-connector plug, like an old iPod Shuffle or an iPhone 3 headset. The remote appears to have 12 buttons controlling several functions. It also has 3 LEDs indicating which input channel is selected, so it is evidently getting something back from the device.

There are some contraints in working on this: This is for a friend; I have access to his recorder but do not feel comfortable opening it because he depends on it professionally and I can't risk damage or voiding the warranty. I also don't have the company's remote itself (which costs $40 that I am trying not to to spend) to mess around with. So I have to  guess about how the remote works then try things out non-destructively.

I can imagine various ways this could work, all of which have problems as theories.

--One is that one connection is a ground and that the device looks for various resistances from ground to the three terminals. I know some camera remotes and iPod connections work this way to signal various states on one circuit, switching in resistors of different values.

--Another would be a keyboard encoder on the remote so that it presents binary words representing the various button presses.

--Yet another would be serial data exchanged with the device. Given that there's almost certainly a processor in there, this wouldn't necessarily be hard for the designers to implement.

Any experience out there with similar devices? Thanks for any ideas. --Dan M

amspire:
It is under $25 on Amazon, and second hand it may be available under $15.

http://www.amazon.com/Zoom-RC4-Wired-Remote-Control/dp/B0027UVTQA/ref=pd_sim_MI_2

It obviously uses a custom digital serial protocol, so I just do not think it is worth the effort to reverse engineer it.

I have a Zoom H2 which does not have the remote control. I usually just start it and leave it running if I am recording. I end up with lots of rubbish that has to be edited out, but that's OK.  Do you want to be able to switch between record and playback without having to touch the Zoom?

Richard.

Edit: Of course if you want to reverse engineer the serial protocol for the fun of it rather then to save money, go ahead. It is probably not too hard if you can get your hands on a digital scope, and they could easily be using standard remote control IC's, except they have a wire connection rather then IR Led. But it may be impossible if you cannot borrow a RC4 remote.

amyk:
If it was a standard serial protocol it would likely be I2C. 1 wire for power, 1 wire for ground, another two for SDA and SCL.

drm1:
Thank you for these suggestions, which make sense. I am not sure I feel like tackling the serial protocol, and this would definitely need a working remote to sniff it out, as you say. The device can record for so long that it might really be best just to leave it on and then edit out unwanted time.

Still, if I can find a cheap working remote I could start with that and rig wireless button presses . . .

I remember when portable cassette players had a jack for a remote switch on the microphone--simple spst that turned the capstan motor on and off directly. --Dan M

amspire:
Basically, you can note the exact time you start to record with the H4n. Then while you are recording, note down the time of events, such as likely edit points.

It is then dead easy finding the edit points.

I remember this great little Olympus water-resistant pocket camera I bought back in the film days. It had a button-sized remote IR shutter trigger, and I felt I just had to have it too. I might have used it once, and it kept on getting lost. It just was not as good as it sounded. Quite often accessories like the RC4 also sound like they would be great.  In reality, when you want to start recording, you will look at the front panel to make absolutely sure it is recording. Then you will not want to touch it. When you start messing with remotes, that's when you will think it is recording, but it is in some other mode instead.

Richard.

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