This is my project for the winter. I have attached the article in PDF format. Part one deals with the component selection, circuit design building the circuits. You can find it here: http://www.eaelec.com/zscale/Part_1.pdf If you want to see my first attempt at modifying a coach, you can find some pictures over at the Canada-Z Yahoo group: http://ca.groups.yahoo.com/group/Canada-Z/
I was wondering if you have you given any thought to using a current limiting diode in place of the regulator and resistors? That's been my plan for my coaches. Mark
Another interesting voltage regulator is the MC33375D, not so easy to find but having as big advantage a Control ON/OFF input Pin. I have the 2,5 Volt version and it seams that for the moment I am the only customer for it. Very interesting IC that I connected already after an Atmel uP and it is working fine. Could also be used to be controlled by a decoder : http://www.ebay.de/itm/400460967995?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
No, I hadn't thought of using them before I saw you post. I looked at the datasheet for the 1n5305, there is a parameter called maximum limiting voltage which I don't understand.
I hadn't thought about CLDs for decades (literally!) until an article in the NMRA last spring. It's a good tutorial and I recommend it. Also Central Semiconductor http://www.centralsemi.com/content/product/cld/index.php , a supplier of CLDs, has some good application notes. You can also use a couple of resistors and a JFET for a multiple device solution. The maximum limiting voltage is the maximum voltage across the CLD which it will still regulate to the specified current. If you consider a white LED that will have a Vf of about 3.6 V, you only need a 5-6 V maximum limiting voltage for Z. I'm considering a higher voltage as I will probably be upgrading to DCC and a CLD solution should work with DCC voltages. My biggest concern is purchasing the CLDs. To avoid the high distributor prices, I'd need to buy 100, which is far more than I'll ever use. Mark
Oh, I forgot to mention that regardless how you power the lighting, I'm anxious to see your mechanical work. Mark
Back to Work Again After a long delay I'm getting back to this project. Part 2 should be ready some time this week. After installing 2 LEDs in one car just to find out if the concept actually works (it did), I realized doing the whole train that way was going to be way to tedious. So I laid out a printed circuit board with a CAD program an had it fabricated.
At the top of the photo (in the previous post) is the bare PCB which contains 27 individual circuits. Below you see some built-up boards which have been cut apart. To the rigth of the penny are 2 LED coach light boards (the small ones) and one 3.3 voltage regulator board. To the left of the penny are 2 constant intensity head-lamp circuits I made to upgrade by old Micro-Trains F7s. These boards have LEDs on the top and the voltage regulator on the reverse side. Here's an upgraded F7 with the shell removed: