DMC v4 Board Details
I’m probably dooming myself at this point, but I’ve completed a layout for the v4 PCB. The v4 has some new features to make the controller more universal, and some things to make it easier to incorporate in a project.
- Onboard DC Power jack (center negative)
- 8-pin MIDI Out jack, with AxeFX phantom power capability
- LED driver chip, allows 8 LEDs in addition to standard I/O
- 8 analog inputs, separate from the LED circuit
- 8 digital pins, each configurable as either input or output.
The earlier rev boards were built around the DMC-6 requirements, so they only had 6 digital inputs for the footswitches. I “stole” the analog inputs for more digital pins to turn on LEDs, but I left one unused input of each type for future expansion. Based on comments from customers, I need more analog inputs for sending CC to synths and FX units!
The v4 board has eight 10-bit inputs that read 0-5V in approximately 5mV steps. Since MIDI CC is limited to a 7-bit value (0 to 127,) we get about 8 times more resolution than we need, no problems there.
The new LED driver circuit is a constant-current LED driver that is controlled by a serial shift register. We stream serial data to it and then flip its /LE (latch enable) pin and the chip will turn on all the LEDs we want just like that, BAM. I’ve got a really simple function that will either change one LED at a time or change all the LEDs at once based on an LED value array. It’s incorporated in the firmware for the v4 board but I will also make it available separately. There is also a solder jumper on the bottom of the board that ties the driver’s /OE output enable to digital pin 12 so that you can PWM the LEDs to change their brightness in real time if desired.
Finally, the housekeeping stuff: The DC power jack is moved onboard, and the new 8-pin MIDI jack has its pins 6 & 7 wired to the DC power input. All the power inputs (onboard jack, MIDI jack, USB 5V) are diode-OR’d so that hooking up more than one power source can’t backfeed and blow up something else. Hopefully. Don’t do that, anyway.
If the Osborne Effect doesn’t destroy my sales, I should have the new boards in the store in May. Completed controllers will ship with the old boards until they’re gone, since they don’t leverage any of the extra functionality in the new boards.
Once the new boards are here, look for a larger MIDI controller with more expression pedal inputs and fun stuff like that…