DL11 MIDI interface.
Designed and prototyped by John Wilson, Bennington College, 1991.




		       Vcc (+5VDC)
			^
			|
 +--- 2.2 K ------------+
 |			|
 |		       /  C
-+-- 470 ohms ------ 2N2907
TTL TxD H	   B   \  E
			|
			+------- 220 ohms ----->

			+------- 220 ohms ----->
			|
			=
		       gnd


				       Vcc
					^
		    +-------------------+
		    |			|
		    |		       1 K
		+-------+ 12		|     6 +-------+ 2
TTL RxD L (note)| _   D |---------------+-------|\    +-|--+--- 220 ohms -->
----------------| Q	|			| | = V |  ^ 1N914
	      8 |    CK |-- 1 MHz osc. (8)  +---|/    +-|--+--------------->
		+-------+ 11		    | 5 +-------+ 3
		    |			    =	  6N138
		    |  Vcc		   gnd
		    +---^
		1/2 7474

note: this flip-flop is being used as an inverter just so we
don't have to add another chip.  the clock is 32x the baud rate,
which is 2x faster than the UART samples so we can safely neglect
the distortion of the input signal.


		   Vcc
		    ^
		    | 1
EXT CLK	      5 +-------+ 2	+-------+
----------------| Q   D |---+	| 1 MHz	|
		| _	|   |	|  xtal	|
	    +---| Q  CK |---)---|  osc.	|
	    | 6 +-------+ 3 | 8 +-------+
	    |       | 4     |
	    +-------)-------+
		    |  Vcc
		    +---^
		1/2 7474

Vcc: (with .1 uF to ground)
7474 pin 14
crystal osc. pin 14
6N138 pin 8

gnd:
7474 pin 7
crystal osc. pin 7
6N138 pin 5 (as shown above)