j Wales's Midi card
Bonjour Does anybody know how I can use the expression output port to drive solenoids with different velocities? For a glockenspiel or drums,for example, it would be better for the music. Thank you very much Chris

Bonjour Chris This reply has been a long time coming and I checked the facts with John Wale before going into print. The velocity or expression output from the MIDI board is presented as a reference voltage, ranging from 0 to about 3 volts in 16 steps. The expression voltage refers to the note output being played at that instant in time. Although the MIDI board might appear to output several notes simultaneously, in fact it switches on each note one at a time, very quickly. The velocity output thus changes very rapidly as different notes with different velocities are swiched on. The way to use this output to vary the impact of solenoids for drums, glockenspiel etcetera, is to devise an electronic circuit which will capture the velocity information at the same instant as the note for the drum etc. is played. This captured reference voltage can then be used to control a chopper circuit that varies the power to the solenoid. It might be possible to have a simpler circuit than that, using the captured voltage, stored on a capacitor, varying the output of a driver transistor. It is not a device I have ever needed to use, but it sounds quite possible to do. Where just one note output is being controlled for velocity, it can be a note on its own MIDI channel. If all the notes on the same MIDI channel are being controlled for one device, such as in a glockenspiel, one control circuit can be used for all the notes. It might be more complex to have the one MIDI board controlling other notes on different channels at the same time. In brief, Christian, It is possible - but it is quite a complex job to do. Bob Essex

A neat solution, Bob, but is there any real point in varying velocities at all? After all, you are really implementing a more modern method of playing mechanical music than books or rolls, where the only velocities are "off" and "on". Drums or a glock will have their pneumatic action - won't they? - whereby you can adjust once and for all the desired striking velocity. Regards, John

Salut! Thank you Bob for trying to respond to me. It seems not so easy to use the volocity control! I think a easier way would be to have as many expression outputs as outputs on the midi card....Dream? An another way I thought is, for example, to put 3 sticks and 3 different solenoïds on the snare. So, by programming the midi file and using 3 different midi notes, you are able to have 3 levels of velocity. (or more if you want). For answering to John, yes it is important to implement expression on a midi drum or midi glockenspiel. I don't want to make an "imitation" of old organ, but a really new musical instrument. I think that 3, 4 or more levels (not necessary 128) of velocity could be a good improve to the mechanical music. I do hope to be able to show you one day. Best wishes to you all. Chris