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MIDI and the Accordion

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W.E.M. Accordion MIDI Interface units. - Type uMID1.

 This note will give a list of all the functions available to the user and installer. 

 General facilities and some good reasons for choosing the WEM system

 The WEM uMID1 series of MIDI interfaces are designed for standard piano and diatonic type accordions and Melodeons but may also be used on any standard piano style keyboard requiring up to 7 octaves of (non-touch sensitive) notes (See power up option 5). In both types of accordion the chord and bass sections are the same, the main keyboard varying appropriately. The melodeon has its own similar connection arrangement. The one interface board may be configured for either type before installation with one connection if not ordered preset.

 The interface is an extremely small (1-3/4" x 3-1/2" x 1/2") double-sided, PTH, glass-fibre, (i.e. robust and high quality) printed circuit board and may be used with the minimum of disturbance to the appearance of the accordion, no external controls being required. Only the lead out connection, which requires a minimum of 4 wires but is normally supplied with a standard 6 pin Din connector and lead which makes work on the connectors straight forward. The two extra available wires being used for 2 selected functions from the 9 available for performance control of the MIDI accordion, but may be ignored if not wanted. 

 For the installers use, there is an `activity light' on the interface board which stays on once normal operation is achieved but flashes off when an active key contact is changed (to On or Off) or a MIDI message is sent. This will help verify proper functioning of the key contacts and whole system. The notes are arranged in octaves for easy (intuitive) installation. ie twelve contacts share a common contact or bus together. The right-hand covers up to 5 Octaves (switchable to 6 - see function F5), the chords 1 octave and the bass 1 octave (switchable to 2 - see function F9). 

 The chords have our unique complete chord detection system (CCDS) which determines when a complete chord is on or off and this gives crisp chords and virtually eliminates contact bounce and double triggering in the chord contacts. 

 The interface can be used with a number of different sound-modules, expanders, synthesisers, work-stations and home keyboards that use different types of auto-accompaniment systems. e.g. Yamaha home keyboard system.

 Nine pads are provided for the connection of foot-switches for activation of up to nine performance related functions. Two of these are available for footswitches immediately at the jack-sockets on the power box.A  MIDI volume control may be implemented using a rotary encoder or an up and  down button .A `telephone' style key-pad may be connected for direct numerical input of functions. E.g. patch change. 

 The unit is polarity protected and consumes very little power (30mA) and may be powered from any rough DC supply of 7.5 to 18 Volts. WEM supply a robust, short-circuit proof power unit which has the MIDI out socket and two jack-sockets for two selected foot-switch functions. In normal use the order of the connection of the leads is unimportant ie you can unplug and plug back in again at any point (though not while playing unless the expander acknowledges active sensing and will turn itself off ! - like the WEM Midi Partner Accordion Expander). 

 Starting from version 1F (and a few of interim version 1E), we now use a reprogrammable micro-controller integrated circuit (IC). This means upgrades or changes are easily made by sending the main IC back to us for reprogramming - (rather than throwing it away). The system version is usually written on a label stuck to the top of the micro-controller IC. If not, it can be determined by electronic inspection of the IC by us. The functionality and performance are the same or better than the previous devices used.

 Normally the interface can process notes faster than MIDI can send them, and so causes no extra discernible delay. e.g. scan and process of whole keyboard in less than one milli-second (<1ms). 

 MIDI outputs - General for Standard Piano Accordion  when powered up in the basic configuration, the default settings from the accordion are :- 

 The Bass is transmitted on MIDI channel            -  3.

 The Chords are transmitted on MIDI channel         -  2.

 The Main right-hand is transmitted on MIDI channel -  1.

 A copy of these on channels 4, 5 & 6 (called expander 2) is also sent.

A (Foot)-switch (normally-open contact, button, foot-switch etc.) may be connected between the pads marked F1 to F9  on the interface PCB (printed circuit board) and the common (ground) to perform the following functions whilst the accordion is being played :-

F1 - Increment (ie increase by one) the MIDI program (patch) change.

 F2 - Decrement (ie decrease by one) the MIDI program (patch) change.

    - This pair send the Midi Program change message on channel 1, starting at    0 at power up, so the first increment sent will be to patch 1 OR the first    decrement sent will be to patch 127. How your particular expander    interprets this will vary from make to make. 

 F3 - Sends the MIDI Sustain (as in piano sustain pedal) message on channel 1    for the right-hand keyboard. (also sends it on channels 4 & 5 if selected, see function F7). 

 F4 - Sends the MIDI Pitch-bend message on channel 1 for the right-hand    keyboard. This pulls the pitch down a semitone (or as much as you set your expander) whilst the foot-switch is held down and when the foot-switch is    released the note slides back up to pitch. (also sent on channel 4 if selected, see F7). 

 F5 - This moves the register of the Right-hand keyboard only (channel 1), Down    by one octave. This increases the players playing range accordingly. 

 F6 - This turns off (mutes) every thing on the right-hand keyboard. 

 F7 - This enables extra MIDI outputs for the right-hand to bring in another    layer of sound or extra sounds as follows :-

    On channel 5 the top note only (or Solo note) is sent (mono-phonic output).    This note is held until released even if a higher key is played whereupon a    new key must be played.

    On channel 4 a complete copy of channel 1 is sent ie a fully polyphonic out    put to the expander.    Also on channel 5 a copy of the chords and on channel 6 a   copy  of the bass.

    To summarize : when F7 is on the complete MIDI output of the interface is as follows :- 

    The Main right-hand is transmitted on MIDI channel      -  1.

    The Chords are transmitted on MIDI channel                  -  2.

    The Bass is transmitted on MIDI channel                        -  3.  

    The Main right-hand is transmitted on MIDI channel      -  4.

    The Chords are transmitted on MIDI channel                  -  5.

    The Bass is transmitted on MIDI channel                        -  6.

    The Right-hand SOLO is transmitted on MIDI channel   -  7 

    The users sound expander module is simply set to receive the wanted parts the others are just ignored as required. The extra channels could be sent to another expander which is why we refer to this function as expander 2.

  F8 - Attack increase. This function increases the velocity amount of the right-hand as if you were playing harder on a touch-sensitive keyboard. The main effect is an increase in loudness. Channel 1 (& 4 if selected). 

 F9 - This will move the pitch of the bass down half a register. this will help to offset the affects of playing within one octave range all the time. This is except in keyboard or non-overlapping note sets modes when this function becomes MIDI Start/Stop. (See power up options). 

 In diatonic mode there are two differences to the function of F5, namely :-

      There is no Solo (top note) output but a fully polyphonic expander 2 output on channel 5.  All else is the same. In keyboard mode F6 is strapped low to set this mode and is not used. F9 is MIDI Start/Stop. All other functions are the same.  

 The interface sends MIDI Active Sensing, which is a message which ensures that if the accordion and the expander become disconnected for any reason then the expander shuts off all sound outputs.  

Using different sound expanders and home keyboards etc. 

 An accepted standard has grown for accordion MIDI settings which assigns the 3 different sound producing areas of the accordion to 3 different MIDI channels allowing maximum isolation of the 3 parts on MIDI multi-timbral expanders. However there are some good home-keyboard/organ derived keyboards which some people like to use but which have different assignments to their sections. The right-hand sounds can usually be set separately to channel 1, but the chords and bass or any derived automatic accompaniment are often all on one channel together. The distinction of sound types is then done by range of notes. The power-on-options below (2,3,4) allow the bass, chords and right hand to be sent in non-overlapping ranges and on the same channel(s), so these keyboards can be accommodated. 

 Power on options.  - These are never normally needed in normal use but are useful for diagnosis of system problems or servicing.

 To setup the interface for use in different modes of operation just before playing, some `Power on Options' are provided. These are accessed by holding down a key and then applying the power. With reference to the other sections of this note, the available options are as follows.

 1) If mid (2nd) C rh keyboard (C on RH2) is held down during power up, the complete chord detection system' is switched off.  This allows the user or technician to try the individual chord contacts during installation/service.

 2) If mid (2nd) D key held down during power up, chords and bass shift down into non-overlapping sets. -  [bass notes from C 24 to B 35 & chord notes from C   36 to B 47]. - exp2 stays normal.

 3) If mid (2nd) E key held down during power up, as above except chords  (ch2) sent on ch1. ie Rh and chords ch1, bass ch3.

 4) If mid (2nd) F key held down during power up, as above except chords (ch2) and bass (ch3) sent on ch 1. ie The complete accordion is transmitted on MIDI channel 1 in one continuous stretch of notes like an ordinary keyboard.

 5) If mid (2nd) B is held down during power up, then a MIDI test signal is sent out only. This consists of a repeating rising chromatic octave of notes from C to B. It is sent on channels 1,2 & 3 in note on then note off order. Channel 2 is an octave lower than channel 1 and channel 3 is an octave lower still. Channel 1 starts on note 60 ( middle C). The activity light will flash with each note sent at about 2 per second. This facility is used to help check the MIDI system out. To cancel remove power and power up again. 

 6) If 3rd C (Rh3) is held down during power up, then expander 2 is turned on so the extra outputs can be used without a hard wired switch. - From Versions 1K of the system, expander 2 is on at start-up by default.

 7) If Pad F6 is strapped to Com at power-up, the interface goes into `keyboard-mode'. Here all parts are transmitted on MIDI ch1 in one continuous stretch of notes i.e. Starting from low C, the bass is octave 1, chords octave 2, right-hand 1 is octave 3 etc. This means any piano style keyboard of up to 7 octaves can be interfaced to MIDI. Note that it will not be touch sensitive, though a velocity increase can be effected using F8 (Attack) over the entire keyboard.

 8) The diatonic mode is in the power-up options category but is kept permanent by the selection link on the pads marked `Dia' at the top of the interface board.

 9) If the Dia link and F6 are both strapped to Com then the interface goes into `Melodeon mode' and it can be wired to a suitably contacted melodeon. The melodeons 3 areas (bass, chords & right-hand) are sent on the same channels as the other accordions. The control pedals function as on the diatonic accordion.

10.)If the F9 pad is held or strapped low at power-up, the PAD buss will expect the Data Entry Pad to be connected rather than the default Volume controls.          

 Power-up options 7/8/9 are permanent links, the other options though have to be redone every time power is applied, if their effects are required i.e. these settings are not stored or memorized. 

The Volume controls. - These incremental controllers are no longer supported though the facility is still there.

Optional controls for adjusting the volume levels of the parts may be fitted. Either a rotary (i.e. like a standard volume potentiometer) incremental controller or a volume up and a volume down button. The channel defaults to Ch1 - right-hand keyboard (and Ch4 if selected). If a chord or bass button is held down these parts may be adjusted as well.


We recommend installers connect all the metalwork (where possible) to the electronic ground (Common) to supplement screening of radiated EMI and to disperse static electricity from the accordion housing. As with most scanned matrix based multiple contact arrangements, each contact requires a standard signal diode (Typically 1n4148) in series with each contact, this includes the pressure (in/out direction) sensor used in diatonic and melodeon mode which is connected between the RH5 bus and the C note bus. The included diagrams detail the electrical connections.

 In use or in testing, the power cable can be plugged in and out as often as required, without any electronic problems. The best aid to testing is probably a sound expander module set to channels 1/2/3. The MIDI test signal may be invoked (power-up/B-Rh2 key) to check the output side, the activity light will flash continually. If in doubt as to whether contacts are being made, then link the B pad to the RH2 pad directly.

 The complete chord detection system may be defeated (power-up/C-Rh2 key) to help adjust the chord contacts individually. 

 Technical spec. - Summary. 

 Power requirements 30ma (max)@ 7.5v (minimum)to 18V dc. (Recommended 100mA @ 8.5V current limited (i.e.The supplied WEM psu and connection unit).    Reverse polarity protected.

 One contact per note with one signal diode (e.g.1n4148) - arranged in octaves as 12 x 7 matrix. Active scan low to 0V.

  MIDI messages and note ranges. 

 Right-hand on channel 1.    From C 48 to B 107. - 5 octaves.

 Chords (ch.2) note numbers         52 to    63.

 Bass (ch.3) notes                C 36 to B  47.

 Solo - top note of right-hand on ch7.

 Expander2 - copies of Channels 1,2,3 on channels 4,5,6 respectively.

 Right-hand and bass may be switched 12 notes (1 octave) lower (F5 & F9).

 Diatonic right-hand notes from     52 (h'34) to   114 (h'72). 

 Program change   -  0 to 127                     - channel 1.

 Pitch-bend range -  Down 28-   (msb's only)      - channels 1,4.

 Sustain          -  On/Off                       - channels 1,4,7

 Attack (velocity increase) -  from 64 to 112     - channels 1,4.

 Active sensing is sent approx. every 150ms in idle state.

 Start/Stop - when selected.

 No MIDI messages are sent in running status format. 

 Scan time approx. every 0.9ms solo/exp2 off (default), 3.75ms.all sections on. In diatonic mode approx. 1.2ms with solo off. Scan out is active Low. 

 Standard MIDI interface current loop output from pads marked 4 & 5. The numbers refer to the pin numbers on the normal MIDI OUT 5 pin Din socket. 

Refer to the accompanying diagrams and charts for circuit diagrams and contact connections.


Originally the interface could be supplied with a standard 12 key key-pad. We no longer support this but the following is included for completeness.

 The Key-Pad. 

 A twelve button `telephone style' keypad may be fitted to the accordion if required. Our experience is that people prefer not to have such adornments on their instruments and as most functions performed by controls on the accordion are better done by external pedals or the expander modules it is not a popular option but is included for completeness of the system. The * (star) key is the `Enter' or `Execute' key, which activates the just entered numbers. the # (hash) key is the `Cancel' key which clears the numbers entered completely.

  Key-Pad Commands and their numbers:- 

 0 - 127 : These are the standard MIDI patch changes. e.g. To select patch 64,  press 6 then 4 then * (Enter) and program change 64 is sent on channel 1. 

 130     : Pedals connected to pads F1 to F8 become 8 consecutive patch changes starting with the last entered patch change. e.g. from above, F1 is           patch 64, F2 is patch 65 ........... to F8 is patch 72.

 129     : Undoes the above (130) so pedals have their normal assignments. 

 131-146 : Changes the patch change channel. 131 = ch1, 132 = ch2, etc. 

 The following commands were used in testing but are included incase they may be useful ! 

 200's   : Selected bank selects -(automatically) followed by program send of  current program number. i.e. as in complete bank select.

 200     : Bank   0:0 (00:00 GS on RA90)

 201     : Bank 127:0 (7f:00 MT32 on RA90) 

 978     : Send MIDI Start.

 979     : Send MIDI Stop.

 980     : Set to diatonic mode.

 981     : Set to normal mode.

 982     : Solo On.

 983     : Solo Off.

 984     : Non-overlapping chord & bass sets. - for Yamaha QR10 etc.

 985     : Normal chord & bass sets.

 986     : Bass 1 octave down.

 987     : Bass to original pitch.

 988     : Straight (individual notes) chord scan -(defeat  ccds).

 989     : Minimum of 3 notes in before any output chord scan.

 990     : Solo up 1 octave.

 991     : Solo to original pitch.

 992     : Rh octave down.

 993     : Rh octave original.

 994     : Exp2 on.  - if f7 selected.

 995     : Exp2 off.

 996     : Stop active sensing send.

 997     : Reset i.e.- program jumps to reset, as power on.

 998     : All sections on. i.e.- bass,chords,rh,solo,exp2.

 999     : All sections off. i.e.- bass,chords,rh,solo,exp2. (mute all).