MIDI to USB converter junk / beware - Page 1
Forum section: electronics / beginners

author: CaptDon
author_rank: Super Contributor
timestamp: August 21, 2024, 01:11:21 am
content: Another Ebay rip off. The converter has two 5 pin DIN cables and one USB cable. They are unbranded but the trademark is a goofy looking treble cleff. They garble the data and some notes when played on your keyboard MIDI OUT won't even show up on your laptop. One or more notes in nearly every octave go unrecognized. I tracked it down using 'MIDIVIEW' and you can clearly see missing or wrong data. I found an article on the internet which even showed exactly the converter I bought as known to be useless. I looked up 'midi to usb converter notes missing' and got the hit.I haven't tested in detail but I believe the data coming from the laptop USB port is being correctly sent to the keyboard via the 5 pin DIN send cable although it seemed to have a huge conversion delay, as long as a 1/4 note at 120BPM. Yamaha UX-16 and a Roland converter were recommended as good quality and reliable for the job at hand. I have a Roland on order. Cheers mates!!

author: themadhippy
author_rank: Super Contributor
timestamp: August 21, 2024, 01:37:08 am
content: Ah flashbacks to the early days of yammy digital mixers and trying to get the midi control to work using just such cables,after much swearing and phone calls the company we bought it from turned up with a lovely little yellow box that just worked.

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 21, 2024, 05:47:54 am
content: You mean something likethis oneon Aliexpress?I have not used it that much. Only to send midi from an Atari emulator on a Linux machine, and did not notice anything wrong that way. Have to emulate the Atari because the real ones harddisk died and I don't have any spares to replace it. Speed wise the Linux machine is just the same.

author: dferyance
author_rank: Regular Contributor
timestamp: August 21, 2024, 06:56:24 pm
content: Most MIDI / USB converters do not have the requisite optocouplers. Instead, they directly connect GPIO pins to midi lines. Depending on your equipment, it can work, but it isn't proper MIDI and also can fail.It is difficult though, either you pay pro-audio prices for something that will work or you pay cheap prices for something that might work. While the BOM price difference between the two is about $2. MIDI is essentially a very slow UART over a current loop.

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 21, 2024, 07:39:22 pm
content: Quote from: dferyance on August 21, 2024, 06:56:24 pmI have to open up the one I have and see what is used in it.With a bluepill, an optocoupler, a simple 74 ic as a driver and a couple of resistors and you build your own. I'm sure there will be some open source project on the web for this, and if not it ain't that difficult to write your own.I have done multiple MIDI devices way back on 6511, SAB80535 and SAB80537 microcontrollers and they never lost a note or any other midi message.

author: CaptDon
author_rank: Super Contributor
timestamp: August 22, 2024, 02:01:08 am
content: Yes, the one in the picture on PCPROGRAMMER's post is the one I have. I did some extensive testing last night. I verified when sending data from the computer to the keyboard all works well. When sending from the keyboard to the computer it is just a nightmare. Stuck notes, missing notes and worst of all it ignores 99% of the MIDI data sent by my Casio MG510 MIDI guitar. The only data recognized is 'Note Off'. However when I plug the MIDI guitar into the keyboard all works fine, so I know the guitar sends valid data. I have owned this cable for some time using it only as computer data to MIDI out. It was only recently when experimenting with Arturia Analog Lab that I realized the MIDI in function is useless. B.T.W. if you happen to run Win10 the free version of Analog Lab is a real treat. I run the older version 4 on Win7. Hats off to all keeping live music alive!!

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 22, 2024, 06:57:52 am
content: I opened mine up and they could have easily done it right. There is a footprint for an optocouplerIn the designs I made way back I used 6N138 for the optocoupler, but this one needs a 4 pin one. Has to be fast enough for the 31250 baudrate.For the sending I think they used a transistor to drive the receiving end optocoupler, so yes that is very likely to work properly.

author: CaptDon
author_rank: Super Contributor
timestamp: August 22, 2024, 12:48:11 pm
content: Looking at how they implemented the design of that interface cable makes me really wonder about data signal integrity vs. a difference in ground potential between the USB side of the converter vs. the MIDI side of the converter. In the most honest implementation of MIDI a difference in ground potential between MIDI devices causes no ill effects in the data loop since the data loops are isolated at each end via fast opto-couplers. Of course as we all know ground differences in the audio chain is a complete nightmare!!! I wonder if the design engineers of this flawed cable that skipped the opto-couplers made an assumption that everything shared a tightly bonded ground and it all 'kind of worked' in their test lab? My laptop 'floats'. Its only path to ground is a series 2.2Meg resistor to earth inside the charger. When I tested with the MG510 guitar it was also floating since it runs on batteries and I had no audio cable plugged into it. I hope the Roland device allows my MG510 to accurately trigger Analog Lab sounds!! It would be nice to play a 'Hammond B3' via my guitar!! Casio did that guitar right!!! It has velocity, after-touch and can be set to Chromatic only OR true pitch bend!!!

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 22, 2024, 04:26:25 pm
content: Without the optocoupler it most likely does not draw a lot of current from the midi transmitter (your guitar) and with that one also most likely using some open collector or open drain driver it is bound to fail.To make it proper, I think that the resistors R10 and R11have to be removed, and the correct optocoupler needs to be found. R5 probably needs to be a 220 Ohm resistor and D1 a 1N4148. But I don't see an option for a pullup resistor after the optocoupler though, so the design might be faulty.

author: oPossum
author_rank: Super Contributor
timestamp: August 22, 2024, 05:23:42 pm
content: This is one I got about 15 years ago.Optocoupler is a NEC (now Renesas) PS2701-1Resistor on LED side is 220 ohmResistor on phototransistor side is 1khttps://www.renesas.com/us/en/document/dst/ps2701-1-data-sheet-0