External power and/or USB hub power

[ibanman555]

I am moving to try and power my MegaDrum externally and I have only the option of using a powered USB hub. This hub provides 5vdc at 500ma. Only the MegaDrum is connected to the hub, and that is connected to the PC. The unit powers on, but the display is very weak. It appears there isn't enough current to megadrum.

Once I power my computer on, the display is much more visible. I attempted to connect a 9vdc 500ma power supply to the hub, but the megadrum display was VERY bright and displayed white blocks on the screen... I promptly disconnected power.

Looking at the schematics I see no voltage regulator in circuit, and so I am wondering what the best way to wire in external power supply, or other option? Thanks!

[ignotus]

I added a port to connect one of those power banks for smartphones and a switch to flip between power from there or from the PC; you don't want power to come from both at the same time if you're using USB for MIDI (doesn't matter if you're using the MIDI ports for communication). You can even use your smartphone to power the module with an OTG cable - I tried it and it works.

[ibanman555]

That sounds like a great idea, but unfortunately there is no way I can rip my MegaDrum out to add ports and switches now... It's very much buried in a mess of studio gear with cables EVERYWHERE!!!

I could just swap the USB from the hub to my power conditioner pretty easily (but inconvenient) , but I also noticed that the 5 pin din midi connectors have Vcc and ground connected to them in the schematic. Would they be sending voltage when the MegaDrum is powered? Or could I send voltage down my 5pin din to power megadrum? That is an option too... power on pins 1 & 3 and be sent to MD if I wire the cable, as my Midi patchbay is sending that power.

[ignotus]

How are you sending the midi data, over USB or over the midi ports? I assume that over the midi ports, otherwise why the need for power from elsewhere? If you're using USB but you want to use external power because of power spikes or whatever, you need to cut the +5 V line of the USB cable, otherwise you'll overload the module. You could make yourself a y-splitter USB cable, with the +5 v line and gnd going to a power bank and the data lines + gnd to the PC. If you're using the midi port for sending data, just plug the USB port into a power bank or smartphone.

[ibanman555]

Cool, thanks that all makes sense. My particular setup might considered unique... I'll explain.

I have MegaDrum connected USB to a laptop to access and use MegaDrum Manager, and to play thru my drum program. I like to have a visual and using MDM is much more useful than configuration directly MD.

The USB is powering the MegaDrum also, but I don't always need the computer on unless I am using MDM. So I was hoping by adding the powered hub in to the mix I could achieve my goal.

Additionally there is a midi cable coming out of MD and being sent to a midi patchbay, where that goes into the Recording computer. That patchbay supplies +5 on pins 1&3...but I don't want to send power if USB is also when it's laptop is on... Correct? So for now, I just have a smartphone plug into the wall, MD's USB plugged into that, and when I need to configure, swap it to the laptop. I was just looking for an easy, permanent solution. If I had a 5vdc,1A power supply I'm sure the hub would work fine... It just doesn't seem to be pushing enough current.

[ibanman555]

Just looking at the 'pic18f2550' datasheet, it's operating voltage limits are 2-5.5vdc...bummer. I'll look for a power supply with higher amperage than 500ma.... That should give me my desired setup without having to disconnect/reconnect.