Hello!
I have a core module running with two IR-leds. To minimize the amount of cables for my box I’m thinking of integrating my usb midi cable and core into one enclosure and feed the the core directly from the 5V on the midi cable board. Would this be possible?
/Jonas
Hey nzmsim!
The USB-port can deliver a maximum of 100mA (can be increased to 500mA by the host if the device requests it).
So I’d check the consumption of your MIDI-Interface (check the midi interface blacklist) and the consumption of your midibox.
If your devices don’t go above 80 mA, your idea is likely to work.
May I ask why you need IR-LEDs?
Hey nzmsim!
The USB-port can deliver a maximum of 100mA (can be increased to 500mA by the host if the device requests it).
So I’d check the consumption of your MIDI-Interface (check the midi interface blacklist) and the consumption of your midibox.
If your devices don’t go above 80 mA, your idea is likely to work.
May I ask why you need IR-LEDs?
Ok, thanks! What happens if the current goes beyond 100mA? I’ve seen usb-devices such as lamps, fans and even coffee-heaters, are these passive or do they communicate with the HUB to request current? I’ll check the consumption of my MIDI-cable. When i measure current, do I just measure it over +5V and ground on the board or do I have to break the circiut in order to get a proper reading? (I dont want to short out my computer :)) About the blacklist, I saw it after I bought the midi-cable and was a bit bummed my ( ebay no-name cable) was blacklisted. At first it didn’t work but I later discovered it was due to a loose midi IN connector. Fix it and now it works perfectly.
As for the IR-leds, I’m making a scratch controller as the one rasteri made, they are for the quadrature encoder. I just finished my first shoe box enclosed prototype last week and it works like a charm.
Ok, thanks! What happens if the current goes beyond 100mA? I’ve seen usb-devices such as lamps, fans and even coffee-heaters, are these passive or do they communicate with the HUB to request current?
dunno. I guess they’re requesting the current (at least the heaters. 100mA seem to be sufficient for LED-lamps and weak fans).
When i measure current, do I just measure it over +5V and ground on the board or do I have to break the circiut in order to get a proper reading?
Current is charge/time. when you want to measure the current, you have to basically ‘count’ all the electrons that go through the usb-cable in a certain amount of time.
Therefore you have to break the circuit and put your multimeter in between.
what you’ve described was measuring the voltage (drop) across a device.
I dont want to short out my computer
heh… I actually did that some years ago with my attempt to build MBHP-USB-MIDI-Interface (the old one with the AN2131SC-IC). I somehow managed to get a big drop of solder into the USB-socket of the Interface, so that all 4 pins were shorted.
When I plugged it in, My PC was instantly shut off, but he survived it (with the exception of one usb-port…)
About the blacklist, I saw it after I bought the midi-cable and was a bit bummed my ( ebay no-name cable) was blacklisted. At first it didn’t work but I later discovered it was due to a loose midi IN connector. Fix it and now it works perfectly.
I guess it wasn’t blacklisted because of some defective connectors. There might be some errors when it comes to sysex messages, i.e. when you want to program your PIC over MIDI (dunno how it looks like with the new CORE32). If you’re looking for a incredibly cheap and relieable 5-I/O MIDI-USB-Interface, you should search the forum (and the WIKI) for “GM5”.
I just finished my first shoe box enclosed prototype last week and it works like a charm.
nice to hear! keep the work up and post pictures as soon as it’s finished 
I’m glad your PC survived relatively unharmed!
Thanks for the pointers! I’ve measured my core and I read 114mA, so I guess it wont work, bummer. I,ll stick with the adaptor and use a battery pack for when I’m on the go, It would have been nice with a usb powered all-in-one box thou 
I’m glad your PC survived relatively unharmed!
Thanks for the pointers! I’ve measured my core and I read 114mA, so I guess it wont work, bummer. I,ll stick with the adaptor and use a battery pack for when I’m on the go, It would have been nice with a usb powered all-in-one box thou
well, If you don’t want to mess with USB power requests, there is a simple workaround.
I’ve bought a USB-Hub at RadioShack some time ago (GM5*4= 20 MIDI I/Os - yeehaw! (I discarded the Idea after I realized that this would be a slight overkill)).
The cable that came with the Hub had a mini-USB plug on one side (for the Hub) and two (!) USB plugs for the PC.
I’ve attached a picture, so you know what I mean.
I’ve just checked it with my multimeter, and it seems that the power-lines of the two plugs are connected in parallel.
This way, you could increase the max current to 200mA.
I don’t know if this way of increasing the current really works (there is a jack for an external PSU…).
It doesn’t seem to do any damage to the Hub it’s connected to right now.
Perhaps you should search the internet for connecting two USB cables in parallel if you like this workaround.
well, If you don’t want to mess with USB power requests, there is a simple workaround.
Ok! I know I have one of those cables laying around somewhere, so maybe I’ll give it a try. One question thou, the specified input for the core is 7-10V, so if i wanna try the USB-mod must I bypass the voltage regulator? If so would this be possible without desoldering any components? maybe by connecting thp 5V from the USB to J2?
maybe by connecting thp 5V from the USB to J2?
yep. J2 is your port of choice.
I’d desolder the 7805 anyway. just to be sure.
And take care of the polarization!
That’s what J2 is there for (among other things). It’s generally advised to remove the voltage regularot and bridge pins 1 and 3 (in and out) if you do that. Then again - don’t do it. USB is really not meant to power stuff with a current draw >100mA.
The thing with the Y-cables is that you need to connect it to two different ports on the PC side. Not just two usb sockets, but two individual ports. The USB ports on a lot of mainboards are all connected to a hub internally so they may just be the same port - with a total of ~100mA to be used.
Thanks nILS and SLP for your answers! Think I’ll just go with battery/wall-adaptor solution.
