building usb-remote-cable

vine

124
A560

Re: building usb-remote-cable

« Reply #90 on: 07 / May / 2008, 03:31:38 »

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Quote from: flaquito on 07 / May / 2008, 00:02:02

Like databoy said, a zener diode is the best way to do this. Have a look here, near the bottom of the page for a schematic.

Since we don't know the specs on the cameras, it's hard to say what resistor value to use, but a 50-100ohm, 1/2watt resistor should work well. Someone feel free to correct me if I'm wrong, though.

Actually using a linear regulator like the 7805 is much more reliable and simple. You don't have to "guess" any part values like you just did and it is much easier for beginners to use in their own circuits. The linear regulator will also output to specification independent of other parts being added to the circuit. These and other advantages make linear regulators much more preferable over rather primitive zener diodes.

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fudgey

1705
a570is

Re: building usb-remote-cable

« Reply #91 on: 07 / May / 2008, 14:57:10 »

Well actually a zener really is the superior choice of the two unless you add a power switch to your remote.

With a zener, you can just wire up the zener and a current limit resistor and a switch. The voltage will be a bit inaccurate but that's no biggie as long as it's high enough for your camera and below 5,3 V or so.

For a 7805 regulator to work properly in-specification you'll need about 7 to 7,5 V minimum input voltage (it will work with less but it's out of the manufacturer specified range...I'm just pointing out that there is no such limitation for a zener) and approx 0,33 uF tantalum minimum in both input and output.

Now, a 7805 draws a significant quiescent current even if you don't actually load it. That's why you'll need to switch it's input voltage off when you aren't using the remote. The alternative is of course to use the remote button as an input power switch as well, but then you'll be charging/discharging the capacitors each time you press your button. That's a waste of precious battery charge and may screw up the USB supply voltage rise/fall waveforms.

All in all, the regulator approach is inferior and it needs more parts and it is more expensive.

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vine

124
A560

Re: building usb-remote-cable

« Reply #92 on: 07 / May / 2008, 19:07:04 »

A 7805 is like 10 cent and you don't need the capacitors for trigger usage, only if you want to charge from your circuit as well. Refer to my schematic for proper wiring and usage. In fact using a linear regulator is easier, uses less parts, is less sensitive to modifications of the circuit and much more reliable from my personal experience of using them in USB applications since the 1.0 standard. But if you abolutely want to use a zener regulator then go ahead, just don't try to preach it as the one and only truth.

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databoy

Re: building usb-remote-cable

« Reply #93 on: 11 / May / 2008, 01:59:41 »

Vine,

I do not know where you obtained your electronics knowledge from. Fudgey is correct and you are wrong. 7805's are switching regulators. Momentarily powering up a 7805 can cause long term damage. They are not designed to be momentarily switched on and off. According to National Semiconductor's application notes (they design and manufacture the devices), regulators need at least a 10uf tantalum capacitor on either side of the regulator legs to stop parasitic oscillation and a bleed resistor to discharge the residual voltage when powered down.

The recognised electronics industry, electronic circuit for momentary use where voltage reduction is required is a zener diode with a series resistor or a power zener configuration.

If you want to use the 7805 regulator approach that is you choise, but do not post your circuit and recommend it to electronics newbies. Long term it will damage the camera.

If you want to get into an electronics technical debate, I will post the full National Semiconductor application note on the correct use of regulators.

What does USB standards have to do with voltage regulators. They are two different standards and applications. The USB 5 volt supply is filtered and certified. The USB bus derives its power supply from the motherboard 7805 regulator which has the appropriate filter capacitors and parasitic line filter inductors built into the motherboard.

When you plug into a USB port the 5 volts is permanently powered, hot wired. The USB CHDK trigger is only sending an external 5 volt supply to a Canon camera to wake it from its sleeping state. There is no USB compliant signal involved; only a 5 volt sensing circuit built into the camera.

Strictly speaking the USB standard is about data transmitted and receiving using USB standards protocols. All you need is serial out, serial in and earth. There is no need to have the 5 volts other than a consumer convenience. The low current 5 volt supply is there for convenience purposes to power low power 5 volt devices. The appropriate USB serial drive voltage protocols are generated by the USB serial circuity.

The freedom of choice is an individual choice. If you wish to recommend your 5 volt regulator approach that is also your responsibility. That means if someone damages their camera using your circuit, you accept the pubic liability responsibility and pay for the camera repairs.

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wrybread

15

Re: building usb-remote-cable

« Reply #94 on: 11 / May / 2008, 04:18:54 »

Strange how its so common on this forum for people to insult each other. Sheesh, we're all just noodling around with our cameras, just state your info and leave it at that. No need to insult or try to scare people.

> If you wish to recommend your 5 volt regulator approach that is also your responsibility.
> That means if someone damages their camera using your circuit, you accept the pubic
> liability responsibility and pay for the camera repairs.

This is so absurd its almost funny. Can you think of a single instance in the entire history of the internet where this has been the case? Where some person (not a company) posted their notes on something and was sued for being wrong about it?

In all seriousness, disclaimers noted.

Parenthetically, my wireless doorbell circuit using the fearsomely dangeround voltage regular has been working fantastically.

BUT ABSOLUTELY ON NO ACCOUNT SHOULD ANYONE ELSE USE IT, ITS EXTREMELY DANGEROUS TO YOU, YOUR HOUSE, AND YOUR HOUSE PLANTS.

This all reminds me of this cartoon:

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vine

124
A560

Re: building usb-remote-cable

« Reply #95 on: 11 / May / 2008, 04:28:39 »

Quote from: databoy on 11 / May / 2008, 01:59:41

I do not know where you obtained your electronics knowledge from.

10+ years of actual experience.

Quote from: databoy on 11 / May / 2008, 01:59:41

The USB 5 volt supply is filtered and certified.

Have you ever actually tested todays cheap mainboards USB voltage? It is far from stable. Device designers know about that and build USB devices with appropriate tolerance. There is no way my circuit could ever damage my camera. Have you read peoples reports on this very forum that they are triggering their cameras with 9V straight without ill effects?
That's the difference between theory (which you seem to have read up on) and actual experience.

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user1

20

Re: building usb-remote-cable

« Reply #96 on: 11 / May / 2008, 05:02:08 »

Part of schematics of some DIGIC2 camera (attached). RN4983 has 10 V maximum input voltage.

1.png (27.58 kB, 989x234 - viewed 523 times.)

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fudgey

1705
a570is

Re: building usb-remote-cable

« Reply #97 on: 11 / May / 2008, 05:35:05 »

Umm..

The 7805 is an ancient industry-standard linear regulator (definitely not a switching regulator, which would be very far away from the scope of this forum), which is known as one of the least likely to oscillate. Everyone has used them and still does, there are several manufacturers and hence they are dirt cheap in volumes.

It's fairly unlikely that anyone's going to be able to harm their camera with one of them, decoupled or not. The biggest danger I can see is that if you harm the regulator (ESD could do that but the 7805 is not the most prone IC to die from ESD) or connect it the wrong way around, your camera will likely be subjected to your input voltage (such as a 9V battery) and all the current it can source if the voltage happens to be too high for the camera. Also, if the camera happens to have more capacitance than what you put in the regulator input, you should add a diode across the regulator to be extra safe (to prevent output voltage from exceeding the input voltage after you disconnect the battery).

The 7805 definitely doesn't need 10 uF decoupling, a few 100's of nF in the input is enough, nothing required in the output. Low-impedance capacitors like ceramics are often harmful for regulator oscillation, but that's more important with LDO's. In a switching application like this a high output capacitance is bad for the circuit and minimum recommended values should be used. That said, I still think the regulator is unnecessary unless the camera's USB input happens to have the maximum specified USB filtering (10 uF) in it's input (which it probably doesn't because it doesn't use the USB supply for much of anything) and maximum speed operation is required. And even then I'd prefer the two-switch approach with significantly more than 10 uF in the regulator input.

As for liability to damage, it's the DIYer's own responsibility entirely to select who to trust and what to do and to swallow their own losses. This applies to the entire CHDK... I probably wouldn't run 3rd party software if I had paid $30000 for my camera, but for a cheap powershot the financial risk is insignificant. And I certainly wouldn't blame anyone else for frying my camera unless they deliberately (and thus criminally) feed wrong information to do harm to others, be it for their own financial gain or just plain vandalism. And that's definitely not what's going on here.

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