|The Flatman and Ribbon - Dual Ribbon CV controller|
The main focus is making a controller for modular synth units hence it needed to put out a control voltage relative to the position on the ribbon. Going to my trusty supply of Arduino Pro Mini processors you may know there is a lack of voltage output control. There is a method of creating a voltage output using a resistor ladder and several digital outputs but we wanted something a little more accurate and less output hungry. So I chose the MCP4922 dual 12 bit digital to analogue converter (DAC) primarily because Chip used this one in his ribbon controller project. This digital to analogue converter was cheap and has two converters on it. So it was the dual converters on the DAC that allowed this project to easily have two ribbons.
|The botched job of the MCP4922 Digital to Analogue converter can been seen at the bottom left of the printed circuit board.|
|Showing the back side of the controller unit. The overkill power supply with it's 6 x 1000uF electrolytic capacitors|
I went a little overboard with the power supply. It's based on Ray Wilson's (MFOS) design which I have used before. The Wall Wart Bipolar Supply is a simpler way of getting a dual rail power supply as it avoids dealing with mains wiring. This is because it uses an external 12v AC plugpack or wallwart. I don't think anyone really likes plug packs but working with mains wiring is less appealing plus there is the added cost of the associated hardware. Using Ray's schematic, I replaced the 7812 and 7912 in the design with 7809 and 7909 regulators to give me 9v which is more than adequate for the output voltages needed. If I used 12volts I would be pushing the Arduino's own power regulator to its limit which I didn't want to chance.
|Showing the front panel with the outputs down the left side and the lcd with menu buttons on the right|
Next to the output sockets I've put a rgb led associated with each output. These rgb leds are my favorite led at the moment - the WS2812. What makes this leds nice is you can simply string several together and the library courtesy of Adafruit makes them easy to control. I highly recommend you support Adafruit. I would more if the freight costs to Australia were more affordable. These leds reflect the state of the outputs. The control voltage leds do a colour wheel effect based on the ribbon position. There was a small issue when it came to the software. I use have used one of the processors interrupt timers when running the sample/hold mode but alas the Adafruit library gets upset with me doing this thus during this mode the leds do not function correctly.
The unit includes a MIDI In and Out. Since the Pro Mini has a standard serial interface it makes sense to include a MIDI interface. The unit will act as a MIDI merger allowing all MIDI information coming on the In connector to be thru putted on the Out socket. With the addition of the information from the ribbons. In addition there is a MIDI function which monitors the MIDI in for a MIDI clock and converts this into a pulse on the Aux Output.
The outputs on the controller box are Control Voltage A, Trigger A which are associated with the top ribbon. Control Voltage B, Trigger B which not surprisingly are associated with the lower ribbon and Aux Output. Depending on what mode you are running the unit in depends on what the different outputs do.
|The underside of the controller panel lid. Shows the LCD at top with it's I2C daughter board, button board at the bottom, the rgb leds and output sockets to the right.|
There are various parameters within the menu system. For both ribbons we have:-
- U Lo Volt - sets the lowest voltage value
- U Hi Volt - sets the upper voltage value - note this can be made a low value and the U Lo Volt can be a high value thus creating a reserve direction ribbon
- U Trigger - whether the trigger output is Trigger or Gate - trigger will simply pulse when the ribbon is first pressed whereas Gate will hold the trigger pulse high until released
- U Hold - set this On and the control voltage output will be held at the last value otherwise it will revert to the U Lo Volt value
- U MIDI Ch - this is the MIDI section and this value sets the output midi channel
- U MIDI CC - this is the controller value that this ribbon will output on
- U MIDI low - the minimum value to output
- U MIDI high - the maximum value to output
|The USB end of the ribbon platform which I am very proud to have made work and look good|
|This the Cut2d shaded preview of the USB end of the platform. The pcb was made to the same shape as the large internal cutout but less 0.5mm in size so that it was a tight fit.|
|These two pieces were routed from 3mm black acrylic and adhered on their joining edge.|