MIDIbox Hardware Platform, LED/Thru/COM Module

This module is expired as the RS232 port isn't useful for modern PCs anymore.
An alternative PCB for MIDI IN/OUT LEDs and 2nd MIDI Out + MIDI Thru doesn't exist, but the circuit can be easily built on a veroboard.

The LTC (LED/Thru/COM) module is a multi-purpose board which provides:

a MIDI IN LED driver
a MIDI OUT LED driver
a MIDI THRU port driver
a 2nd MIDI OUT port driver
a MIDIbox-to-COM port (see MIDIbox-to-COM page)

Mostly not all chips have to be mounted. Following two configurations are useful:

1) you want to monitor the MIDI In/Out activity with LEDs and you need a second MIDI Out and/or a MIDI Thru for a particular MIDI device (i.E for a second PC) - in this case the LTC module acts as a passive MIDI module with a Tx Input and a Rx Input. You have to stuff the two 74HC00 which drive the LEDs and the additional MIDI ports (beside of the resistors and capacitors)

2) you want to monitor the MIDI In/Out activity with LEDs and want to connect your Core module to the RS232 port of a PC/Mac - in this case the LTC module acts as an active MIDI module with a Tx Input and a Rx Output which supplies the Rx Input of the PIC. You have to stuff one 74HC00 for the LEDs and the MAX232 (beside of the resistors and capacitors), and you have to remove the optocoupler from the Core module in order to avoid a short-circuit (only one driver is allowed for the Rx Input of the PIC, either the 6N138, or the MAX232, or a second Core module)

Here an additional example to give you an understanding how a serial MIDIbox Link between two or more CORE modules has to be realized when the To-COM option (MAX232 stuffed) is used:

And here an example how the To-COM option works with MIDIbox SID Master/Slave module(s):

Download

PCB data, can be viewed, modified and converted with Eagle Light. The .pdf based schematic has been created with xcircuit. There are no special eagle schematics available, since components have been netlisted in the .brd file directly!
Module	Schematic	Layout Data	Quick-view
MBHP_LTC_V1	mbhp_ltc.pdf	mbhp_ltc_v1.brd	mbhp_ltc.gif

Additional informations
File	Size	Description
mbhp_ltc_orderlist.txt	1k	Reichelt orderlist
MIDIbox-to-COM	LINK	The MIDIbox-to-COM Interface

Available Ports

Following interfaces are provided by the LTC module:

Name	No. of pins	Description
J1	4	Interface to CORE:J11 - power input (0/+5V) and Rx/Tx signals.
J2	2	+/- connection to the MIDI-IN LED.
J3	2	+/- connection to the MIDI-OUT LED.
J4	3	MIDI THRU port. See the schematic, how to connect a MIDI socket to this port.
J5	3	a second MIDI OUT port. See the schematic, how to connect a MIDI socket to this port.
J6	9	This is the interface to the COM-port of your PC. A 9-pole sub-d socket (female) has to be used.

Used Components

Here a list of the used components. A complete orderlist for Reichelt can be found here, Mouser partlist for the US: see SmashTV's Website, if you have a orderlist for a distributor on your country, feel free publish it on this page!

Part Name	Value	Description
IC1, IC2	74HC00	4*NAND gates, used as driver for LEDs and MIDI ports
IC3	MAX232	a RS232-port driver which converts 5V to +/- 12 V --- only necessary if MIDIbox-to-COM option should be used.
R1, R2	470	series resistance for the LEDs. Without these resistors the LED would be destroyed!
C5, C6	10uF	charging capacitors for the monoflop circuit. If you prefer fast flickering LEDs, lower the values to 1uF
C7, C8	100nF	The additional bypass caps have to be placed on the bottom side of the PCB, as close to the +5V power input of the 74HC00 as possible.
R3, R4	100k	decharging resistors for the monoflop circuit, value should not be changed in order to avoid high decharging currents.
R5, R6, R7, R8	220	protection resistors for the MIDI ports, they limits the current if the MIDI ports are shortened by fault.
C1, C2, C3, C4	100 nF	capacitors for the charge pumps of the MAX232. Not necessary if the to-COM option of the LTC should not be used.

Soldering Guide

	Start with soldering the 5 bridges which save you from creating a 2-layer board. You can use the cutted legs of caps and resistors, before you throw them away after you finished all the modules! :-) Note that for one bridge an isolated cable has to be used, since it crosses another bridge
	Stuff the resistors, capacitors, sockets, connectors.
	Add also the two additional Bypass Caps between Vdd and ground (Vss) of each 74HC00 on the bottom side of the PCB as close to the +5V power input of the 74HC00 as possible. They improve the power integrity.
	Connect the LTC to the Core module and check the voltage levels on the IC sockets: IC1:Vdd(14) - IC1:Vss(7) = 5V IC2:Vdd(14) - IC2:Vss(7) = 5V IC3:Vdd(16) - IC3:Vss(15) = 5V
	Now stuff the two 74HC00 if you want to use the LTC module like descriped above in option 1)
	Don't use the optocoupler and the MAX232 at the same time!
	Stuff the MAX232 if you want to use the LTC module like descriped above in option 2)

Last update: 2023-11-04