Electronics for operating turnouts and signals


The MD88 is a self-clocked multiplexing driver that can generate 2 to 8 phases, each with 8 LEDs connected for a total of 64 lamps.
When operating in its native mode the MD88 drives LEDs only, and can not drive incandescent lamps, relays, or turnout solenoids.
However the MD88 can be operated in the 3 MD2xx modes (direct, common cathode, common anode - multiplexing synchronized to rail sync), but requiring reversable modification to add expanders (see below).
The "fs_" connections are for a possible future expansion of the anode drivers, however the current configuration memory size of 256 bytes makes driving more than 64 lamps unlikely.
Modification note:
The MD88 can be used as an MD28 as it is, to add an expander requires some simple and reversable changes
1) remove both 74HC595 chips
2) jumper pins 9 and 14 of the socket connected to the green terminals
when in MD28 mode the 3 leads used for driving the 74HC595 chips revert to MD2xx expander mode, relabled as follows:
  • fs_clk becomes Data In
  • fs_strobe becomes Data out
  • fs_data (jumpered in socket) becomes Data Strobe

Alternately, instead of jumpering the socket, use a 16-pin IDC connector in either open socket for the following signals:

  • 1-7, 15 are either open or connected via 100 ohm resistor to the terminals
  • 8, 13 ground
  • 9 open
  • 10, 16 +5vdc
  • 11 Data In
  • 12 Data Out
  • 14 Data Strobe
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