I am not sure if I should feel honoured, or if I should moan about plagarism., or neither. You do not mention anywhere on the your site where the electronic design came from, although it is clearly not the DEC one (which used 56 discrete transistors in the lamp driver circuits). So let me guess where it came from.. The first thing that struck me about the PCB was that it has positions for 4 18 pin chips. Now there are not that many common 18 pin chips, the main ones being the 2114 SRAM, some PIC microconterollers, and the ULN2803 (etc) drivers. Only the last would make any sort of sense on this board. And I notice that the components list that this guess is correct. Many years ago I was given a PDP11/45, and while sorting it out I realised how useful it would be to have a KM11 or two. At the time DEC stuff was even harder to find that it is now (there was no E-bay, no world-wide web, etc). Finding a genuine KM11 was out of the question. But I did manage to find the connector board that had come with a DR11-B. This was simply a single-height extended length board with the 36 edge fingers wired to turret lugs. I wired a cable to that, the other end to a DC37 socket. And I made a box that plugged in there with 28 LEds and 4 switches on it that simulated the KM11. Now for something that is too much of a coincidence. I used ULN2803 drivers. I had originally intended to use 7406s, but found the input current was too high to work reliably. DEC, you see, put 1k resistors in series with most of the signals going to the KN11 connector, to prevent the module from loading the signals too much. An even more suprising coincindence is the capacitor I used to smooth the 8V supply. The first one I pulled out of the junk box was 330uF. There was not real need for that value, 470uF would be fine too. It's just what I used. I notice you specidied that value. Some time after I built the thing, I posted details to usenet, and to some other places too. I'll reproduce it again below, for refernce. It is my guess that you have built this board essentially to this design. My problem is that my name does not appear anywhere on your site or on the PCB (AFAIK). I am not sure how much of the design I could claim anyway (it is clearly based on the DEC design, it virtually has to be). And I love these old PDP's, so I am not going to do anything to make it more difficult to people to maintain them, e.g. by moaning seriously about you selling said PCBs. But I am still somewhat unhappy, unless you can show you didn't start from my design. I come from an academic background where it is common courtesy to give credit to others. I also wonder if I should be quite so free with advice and designs in the future. Anyway, here's the original description : How to build a clone of the DEC KM11 maintenance module ------------------------------------------------------- The KM11 is the maintenance module for the PDP11/05,10,40,45 CPUs, RK11-C, RK11-D controllers, RX01 floppy drive, and probably many other devices. It is not commonly available second hand, so if you want one, you will probably have to build it yourself. Here I'll describe how I did just that. Components : 5* 1k Resistor 28 * 330R resistor 28 * red LED 1 * 330uF Capacitor 1 * 7400 1 * 7406 4 * ULN2803 3 * SPDT (single pole change over, form C) toggle switch 1 * SPDT biased toggle switch Prototyping board/PCB (your choice) 1 * DEC M957 cable connector module - this is the single-height connector module that was supplied with the DR11-B parallel port. If you can't get this, you can use anything else that will fit in a single-height slot, and will make a separate connection to each of the 36 pins. Ideas include etching one from PCB, cutting down another DEC board, cutting down an S100 prototype board, etc. 1 * Box (if you decide to make it a separate module linked to the M957 by a cable, as I did. A box with a clear lid avoids having to drill holes for the LEDs) Cable, wire, solder, etc. I'll present this as a set of instructions and part circuit-diagrams. I'll not show the power connections on the IC's - all the pins indicated as ground (pin 7 on the 7400 and 7406, pin 9 on the ULN2803) are linked to ground, Vcc on the TTL chips (pin 14 on the 7400 and 7406) are linked to +5v. The protection pin (pin 10) on the ULN2803 is linked to +8V. I'll also assume you have the pin-outs of the chips, and so I'll not be numbering all the pins Also, note that I use the DEC labeling of pins on the M957 board. Looking into the slot socket, they are layed out as : Solder side Component side A2 A1 B2 B1 C2 C1 D2 D1 E2 E1 F2 F1 H2 H1 J2 J1 K2 K1 L2 L1 M2 M1 N2 N1 P2 P1 R2 R1 S2 S1 T2 T1 U2 U1 V2 V1 Right, down to construction : 1) Power wiring The power voltages are obtained from the slot as follows (B1)-----------+---- +8v | + --- --- 330uF | | --- /// (A2)----------------+5v (C2)--+ | (T1)--+ | --- /// 2) Switches There are 4 switches, all of them slightly different!. I mounted them on the front of the box in which I mounted the prototyping board containing the driver chips an LEDs. S1 was on the left, and S4 (the spring-biased one) was on the right. Wire them up as follows : /o / +-----/ o------(B2) | s1 --- /// +5v --- | / \ 1k / /o \ / | +----/ o----+-----(V2) | s2 --- /// +5v --- | / \ 1k / | '00 +-+------|\ |\ | | )o---+-------| |>o-------(A1) | +--|/ | |/ S3 o | | '06 +\ +-------+ | | \o +---------)-+ | | +----|\ | | | | )o-+ | +--------|/ --- | '00 /// | | / 1k \ +5v / --- | | +-----+ +5v --- | / \ 1k / | '00 +-+------|\ | | )o---+-------(U1) | +--|/ | S4 o | | +\ +-------+ | | \o +---------)-+ | | +----|\ | | | | )o-+ | +--------|/ --- | '00 /// | | / 1k \ +5v / --- | | +-----+ (S4 is spring-biased to the position shown). So, to recap. S1 grounds pin B2. S2 grounds pin V2, which is pulled up by a 1k resistor. S3 is debounced, open-collector buffered, and then drives pin A1. S4 is debounced, and then drives pin J1. All these pins should be high/floating with the switches in the 'off' position. 3) LED's. Mount 28 LED's in a 7 * 4 matrix either on the box lid, or on the circuit board if the lid is transparent. Each LED is driven by one section of a ULN2803 chip - like this : +8v --- | | --- \ / \ RED LED --- \ |\ | V (pin)-----| |>o----/\/\/---+ |/ ULN2803 (1 section of 8). Do not try to replace the ULN2803 device with a TTL driver. DEC put 1k resistors in series with some of the signals, and a TTL buffer will not be driven correctly As I said, the LED's are mounted in a 7 column,4 row matrix. Link the inputs to the driver chips to the pins as shown in the diagram below : K2 J1 P1 R1 S1 N2 R2 N1 C1 L1 K1 M2 D2 E2 V1 T2 F1 S2 F2 H2 H1 P2 U2 D1 M1 E1 J2 L2 Finally : The meanings of the LED's and switches are shown in the DEC maintenance manual or Engineering drawings for the particular device. If you don't know what they are, I may be able to look them up for you. -tony ard at sive.bris.ac.uk ------------------------------------------------------------------ I also wonder if you used ULN2803s becuase you couldn't find ULN2003s in 1-off quantities. That's why I used them :-). The 2003 9s a 7-stage driver (16 pin DIL package) and 4 of them would be ideal for the 28 LEDs -tony