ADB - Device/Power Limits

[thecroc15]

Been thinking a lot lately about what would max out an ADB port. Mostly for silly reasons as I collect random input devices, but also there seems to not be much out there to simplify the ADB equation for non-engineers like myself!

I guess my biggest question is: how easy is it to fry an ADB port by adding too many devices? And then what constitutes low power vs high power devices? My assumption always was that simple input devices like keyboards and mice were low power, and then dongle-vampires like modems/port jugglers/etc are all high power devices.

And to top it off, would a PowerBook supply less power to ADB than say a Quadra or Power Mac?

I promise I have searched, and even read some of the early 90s technical reference stuff (where IIRC three devices was the recommended, but not a technical max). Any thoughts or real world experience appreciated!

 

[cheesestraws]

The limits are documented in one of the books, but I can't remember which one. Might be the guide to the macintosh family hardware.

Vague memories that it's 500mA on desktops but significantly less on powerbooks.

 

[Phipli]

There is also the possibility of using external power for the bus, so you can power more devices, but you'll need to not put too much current through any of the devices.

The extreme would be putting an ADB hub with external power every 5 devices

 

[Snial]

The limits are documented in one of the books, but I can't remember which one. Might be the guide to the macintosh family hardware.

Vague memories that it's 500mA on desktops but significantly less on powerbooks.

A related question is how much power can be taken from a pre-NewWorld Macs' serial port? Because of the TX+, TX-, RX+, RX- pins, it should be possible to provide continual power to a very low-powered device using diode-based rectifier and some capacitors while also being able to use it for serial comms too.

 

[Phipli]

ADB hub with selectable external power :

 

[cheesestraws]

A related question is how much power can be taken from a pre-NewWorld Macs' serial port? Because of the TX+, TX-, RX+, RX- pins, it should be possible to provide continual power to a very low-powered device using diode-based rectifier and some capacitors while also being able to use it for serial comms too.

Officially, none. I looked at this when I was doing AirTalk and it seemed technically possible but I wouldn't do it in any hardware I was giving anyone else.

 

[twelvetone12]

A related question is how much power can be taken from a pre-NewWorld Macs' serial port? Because of the TX+, TX-, RX+, RX- pins, it should be possible to provide continual power to a very low-powered device using diode-based rectifier and some capacitors while also being able to use it for serial comms too.

You described how the digital systems in model railways work! It is basically a serial bus that gets rectified. Doing this on a serial port would be quite some crazy serial port abuse One could look on the current sourced by the transceivers...

 

[chelseayr]

well it is plausible to get quite high but nowwhere close to the 500ma limit yet if you have a keyboard, larger non-wallwart tablet, newer supraexpress adb modem, and the mouse all at once? in theory tho mind you, i'm not sure what the actual averaged total current draw for that would be

 

[bigmessowires]

I don't think it's crazy to rectify signals and use the result to power low-power devices when no other power source is available. I plan to try this approach with the sync signals for the LM1881 Mac-to-VGA adapter. Maybe it's not recommended, but if we're talking about a single digit number of milliamps then I don't see a problem.

 

[CircuitBored]

There are also a few serial-MIDI converters that draw power from the serial ports, presumably also utilising rectifiers.

 

[Snial]

There are also a few serial-MIDI converters that draw power from the serial ports, presumably also utilising rectifiers.

That's handy to know. That's the kind of thing I'm thinking of. Pico power MCU + maybe some flash. It might even be possible to sleep until there's enough power in the capacitor, so that energy usage is bursty in order to stay within bounds.

 

[cleoandroid24]

I bought a program that virtualizes the USB on the LAN network, I have 100 devices connected to a PC through hubs, I want to get these 100 devices and virtualize the USB, but unfortunately, when I do this, all devices appear in the device manager, but in ADB only 15 appear, can anyone manage it? help me by paying for consultancy

 

[cheesestraws]

I bought a program that virtualizes the USB on the LAN network, I have 100 devices connected to a PC through hubs, I want to get these 100 devices and virtualize the USB, but unfortunately, when I do this, all devices appear in the device manager, but in ADB only 15 appear, can anyone manage it? help me by paying for consultancy

I think you are thinking of a different ADB - do you mean the Android debugger?

 

[cleoandroid24]

yes

 

[cheesestraws]

yes

Then you're on the wrong forum: ADB here is Apple Desktop Bus, nothing to do with Android.