Compatability with H-Pi Flash Synth?

[RagingRoosevelt]

I was hoping to use my Flash Synth with Le Strum but I seem to be stumped. Flash requires the MIDI port to follow the MIDI Manufacturer's Association spec. Does Le Strum follow that spec? In particular, this is the part of the spec that Flash cares about:

Power Requirements

FLASH draws its power directly from a standard MIDI OUT socket where pin 2 (centre) is connected to ground, and pin 4 (left of centre) is connected to positive voltage between 2 and 5 Volts. Not all MIDI OUT ports are made according to the MIDI specification. If you have experience with electronics testing, you can check the jack of your instrument using a multi-meter. Plug in a MIDI cable and measure the pins as shown for voltage and amperage output. The pins of the attached cable will match the pins of the jack as shown. Be careful, of course, not to short the pins when measuring, which includes not touching the shell with the probe on pin 4.

source (pdf)

Is this unsupported? Is there a way to get this to work?

[hotchk155]

Hey, you can connect pin 2 of the MIDI out socket to ground if you want to be able to draw power from the MIDI signal lines. The easiest way is to scrape off some of the solder mask from the underside of the board beside pin 2 then add a blob of solder as shown in yellow below. You could also use wire between pin 2 and the battery GND connector.  I would not usually recommend trying to draw power this way since the Le Strum is battery powered and the 5V supply is via a micropower LDO regulator. This means if you try to draw too much current you could stress the regulator and/or reduce battery life. However if your Flash synth draws low current you could give it a try You could also run from an AC/DC adaptor and replace REG1 with a full size LM7805 reg if you have issues. Cheers Jason

[RagingRoosevelt]

You could also run from an AC/DC adaptor and replace REG1 with a full size LM7805 reg if you have issues

The LM7805 would take 120v AC and convert it to 5v DC for the Le Strum?

Would another option be to set it up to use USB power directly and then just tie the midi plug into the usb power? I was originally planning to use a micro usb breakout connected to a step up converter and a 9v battery adapter to USB power the thing, so maybe going directly from USB would work instead?

[hotchk155]

The LM7805 would take 120v AC and convert it to 5v DC for the Le Strum?

Nooo - what I meant is you need to run from an AC/DC adaptor - i.e. something that takes 120VAC and converts it to 9VDC. In addition to that you could replace the micropower 78L05 with a full size 7805 if you needed more current capacity (e.g. reg getting hot or shutting down)

Would another option be to set it up to use USB power directly and then just tie the midi plug into the usb power?

Yes if you have 5V from USB you can power the Le Strum from that but you would have to bypass the on board regulator (REG1). You'd then still need to ground the MIDI socket pin to provide MIDI power to your synth. Don't send 5V directly down the MIDI connection as there needs to be a pair of in-line resistors and you might otherwise damage your synth