Now the basic wiring on Victoria Road is done, I need to install block detection for interlocking and possible automation. I am going to use MERG DTC8 current sensing block detectors and the MERG PMP 7 detectors. Both are supplied as kits, so here is how I made them. First up DTC8 Kit 56 8 DCC isolated current detection sensors How they ever manged to get all the bits into the I'll never know.... This kit will produce 8 current detection sensors. The board also has a Remote Panel Control (RPC) Interface, for this tutorial I will not be using this functionality. The board is designed so that the 8 detectors can be in one unit, or can be split into pairs, this is how I will be building this kit. The instructions are comprehensive and should be read before starting - I know its not manly, but niether is the sight of a man crying, melting the ends of his fingers trying to remove the bits as he forgot to install the smallest part. Tip Number 1 LEDs, Electrolytic & Tantalum Capacitors - the longest leg is the +ve First step (for me) was to split the PCB into 4 dual detector board, and discard the RPC section (left hand section) All the MERG kits follow a similar format start with the smallest components and work up, this allows you to keep the parts flat against PCB when soldering So wire links, followed by resistors, diodes and small capcitors Next the 14 way DIL socket, transistors, electrolytic capacitors and molex connector The fun part the two detector coils, then loop the red track coil wire through the dector coil. Finally fitting the terminal blocks. Before the chip a was inserted (NE556 - dual timer) the board was checked for shorts, dry joints etc. The sensor will work with any voltage between 5 & 15V dc, under 5V and the IC will not work correctlky, over 15 and its liable to fry. Finally, you get this :- Picture above shows a jury rigged detector socket The 4 pin Molex socket is as follows Left to right Pin 1 (white) +5V, Pin 2 (black) 0V, Pin 3 (yellow) Output 1, Pin 4 (green) Output 2. An led is connected between Pin 1 & 3, another between Pin 1 & 4, to give an indication of an output. When installed the leds will not be included. A very rough video can be seen here or the link https://www.youtube.com/watch?v=LgHb-JlK8lQ The timer helps avoid false or iratic readings, once current flow has been detected, the timer maintains the ON condition for 1 second after current flow stops. Just as in real life a section does not immediately clear as a trains exits the section. Paul
And now the MERG PMP 7 A Train detector for DCC This Kit is from the MERG - Pocket Money Projects range, aimed as cheap useful entry level projects to get users into building electronic projects. This kit will use some power from the track, so may cause a slight voltage drop. It does provide an optically isolated output, which should work with a NCE AIU. As this is a stripboard based project, you have mark out the breaks in the tracks, and then cut the tracks, you can buy a tool for this (approx £12 from Maplins, £6 from the bay), or use a 3mm wood drill (my method), or if you must use a knife Once all the breaks are completed, clean the board, and check that there are no stray connections, I use a multimeter with a continuity checker, but Max's Jesus box would work just fine. As with the other builds start with the thinest components first, this allows you to hold them flat agaisnt the board with minimal pressure. So wire links, 1K resistors, 1N4148 Diode, 100K resistors, remaining diodes, TLP521 Opto isolator, ceramic capacitor, DIL socket and the electrolytic capacitor. I did make 1 modification, as the black wire is common to the input and output & the 3rd track from the bottom has no connections, I added a wire link between the 3rd row and 4th row to make it easier to connect the DCC wires as can be seen just to the left of the diodes. I didn't add the LM393 dual comparitor chip, until the board was cleaned & tested. Cost £1.50, plus a hours work. To be honest this took longer than normal as I had to keep counting the holes to get the correct position of each component, but thats normal for this type of circuit. The instructions also give examples of use, driving relays, input boards etc. They also throw down the gauntlet, and set a wee challenge The circuit uses a single LM393 and a single KB814 to create one train detector module. However the KB844 is a 16-pin device that is four different optoisolators in the one package. Likewise, the LM339 is a 16-pin chip that is essentially four LM393's in the one package. So my next project - if Toto ever gives me time, is to build a board with 8 detectors on it, with a direct connection to a MERG CANACE8C 8 channel input unit for the traverser. I now have the CANACE8C kit and several Quad optoisolators and Quad comparitors to try and produce more compact circuit. (I've also got enough single bit items to build as is, if I can't get it to work). Paul
Just a wee comparison on price MERG DTC8 £33.75 for 8 sensors approx £4.22 each MERG PMP7 £1.50 each NCE BD20 £10.76 Digitrax BD4 Quad occupancy detector £27.64 approx £6.91 each Each detector needs to be connected to an input unit compatable with your DCC system. In my case - NCE PowerCab with v1.65 rom, I can only connect 3 non throttle devices to my system, which would be either AIU, MiniPanels or USB interfaces. The v1.28 rom only allowed the USB device to be connected - which was the rom that originally came with my PowerCab. I wanted to have some form of electronic control panel, so needed the USB interface. So I decided to use the MERG CANBUS devices for feedback, connected to the same PC as the NCE PowerCab, all linked together with JMRI PanelPro. I did look at RailRoad & Co, but they dont support the NCE USB interface, so saved several hundred pounds. More to follow ..... as they say Paul
