X-perimental Commodore serial bus transfer cables and adapters

Some links

sta.c64.org X1541-series cables and software
d81.de XA1541 adapter with parallel header

"XPADME1541" multiconfigurable adapter PCB

Choose between XA/E/M1541 compatibility and parallel transfer header. The configuration is "static", but it is possible to swap between XE/XM adapter using a soldering iron to change solder pad jumpering.
Uses "digital transistors" for XA, OR BAT85 (or BAT54 SMD) diodes for XE/XM. But not both diodes and transistors.

Version 1.1

EAGLE "source" project files were accidentally deleted, including the schematic, but here are the PCB output files in gerber and excellon. This board has a place for a toggle switch to select between XM and XE adapter. And places for two DIN-6 connectors (both connectors have the signals connected together, so it is possible to have the adapter somewhere in the middle of the IEC daisy-chain.) Either BAT54 SMD-diodes or 2N7002 FETs can be soldered on board (correct orientation of the sot-23 case part can be guessed from the ground signal, transistor uses it, but diode does not.) The picture shows an undrilled via next to pin 13 of the D25 connector. I needed to fix this manually to make the signal connection for the batch of boards I had factory made. There may be a bug in the excellon drill file, that leaves the via undrilled.

The silk screen markings "XE" and "XM" on the board are with respect to a toggle switch lever position, ie. when lever is turned towards the "XM" position, the switch actually connects the center poles to the pads that are nearer the board edge.

Use 2N7002 instead of BCR133 for the XA adapter

The BCR133 is not fast enough for the XA1541 in all cases. This type is mentioned in the schematics for up to version 0.4. I have not made any BCR133 measurements with an oscilloscope, but a user reported that changing the transistors to another, faster type made a transfer software work. The BCR133 is a bipolar NPN transistor with integrated bias resistors, which make it work at TTL input voltage levels. One possible cause of slowness is because of transistor saturation, which delays the "release phase" of the action of sinking current after the input voltage is lowered to TTL low level.
A possible faster substitute is the 2N7002 which is a N-Channel Enhancement Mode Field Effect Transistor, and should operate nearly with TTL input voltage levels. But in some manufacturers' data sheet says in some cases that the gate threshold voltage is at most 3 volts, whereas TTL input high level threshold is 2 volts (and the output 2.4 volts, where the 0.4 volt difference is noise margin). However the PC LPT port is likely to output 3.3 volts at high level, if the LPT output driver chip operates at 3.3 volts supply voltage.
2N7002 maybe available in many package types, but the one that fits this board is the one in 3-pin SOT-23 package. It is directly "drop-in" compatible, because the "ground", "TTL level input" and "current sinking output" are at the same pins as in the BCR133 (emitter, "base", collector vs. source, gate and drain in the 2N7002.)
Perhaps another possible compatible transistor is the 3-pin SOT-23 version of the type BS170.

Version 0.4

Almost the same as V0.3. Photos: configured as XE as XA

Version 0.3

This version is an update from V0.2, but is untested so far..
PCB layout Schematic Cadsoft EAGLE source files: xpadmev03.sch xpadmev03.brd

Version 0.2

Photo PCB layout Schematic Cadsoft EAGLE source files: xpadmev02.sch xpadmev02.brd
This version is routed with EAGLE's autorouter, and it is not very good for DIY-etching the board. Pad holes for DIN-connector should be edited to be a little larger, like 1.5 mm. Also pad holes for pin header could be a little larger, like 1.0 mm.