Use the instructions from the following pages from RMC mag, and you can construct a great little decoder testor that will only cost a fraction of the price of the ones for sale. I keep mine connected to the program track, so that even when I dont have a decoder attached to the testor, and am writing to one in a loco, I can watch the lights and see when it finishes writing to the decoder. It can handle 8 pin, using a spare 8 pin plug as a riser, 9 pin jst's, and even hardwired decoders just fine. The cost of all the components should only be about $20. http://www.thewhistlepost.com/forums/gallery/data/500/tester1.jpg http://www.thewhistlepost.com/forums/gallery/data/500/tester2.jpg http://www.thewhistlepost.com/forums/gallery/data/500/tester3.jpg http://www.thewhistlepost.com/forums/gallery/data/500/tester4.jpg I hope these help some of you who want to build something for your dcc. These pages were scanned from RMC September 2001. They shouldn't mind them being reproduced like this.
RMC is a published and copyrighted magazine. As such, posting these pictures may be an infringement. I have changed all the pictures above to link back to the website where they are posted. Thank you for your patience. I saw one of these at my club the other day. The member had made it himself. Very nice item to have for DCC.
For A Little Extra Work.... You can add a circuit to help find that PERFECT resistor value to give you the bulb brightness you want! If I remember right, I have about $15 in it as most of the parts were leftovers from "other" projects. NCDaveD
Dave, I do like the idea of the variiable resistor test box portion. That's handy as a standalone item.
Dave, that addition looks great! Do you think you could post up a quick schematic for us lesser fortunate people who can build circuits, but can't really design them all that well? and the voltmeter portion, did you just tie those into the black/red connections in parallel with the decoder connections? Even a standalone version like mentioned above would be a great little idea. Loves me the gadgets, especially ones that are useful
Below is my attempt at a pictorial, not really schematic. I hope it gets the idea across OK. I can't take credit for this idea tho....I saw it somewhere in some magazine years ago as a separate item and just decided to include it in my tester to keep it all in one box. It sure is nice to see the brightness and know for sure what voltage the bulb is at to give it a nice long life. NCDaveD PS After another quick look, just make sure you don't have your decoder set to run the headlight and taillight on at the same time......
Thanks Dave! Now that I look at the circuit, it makes perfect sense now. Think its time to head to the electronics supermarket deal today and do a little shopping
The snag with that circuit is that it gives you results in mostly non-standard values. Eg. you might find 300 Ohms is 'perfect', but unless you go to high accuracy resistors you will then have to choose between 270 and 330 Ohms. I'd be inclined to use a standard resistor wired to each switch contact (not in series with each other) using 100, 120, 150, 180, 220, 270, 330, 390, 470, 560, 680, 820 Ohms. Might be worth having a 1k as well. If I didn't have enough contacts (eg. for the 12 way illustrated) I'd drop some of the lower ones which probably wouldn't see much use, so 0, 150, 180 ... 820, 1000. Added later: As with all test gear the tester should be significantly more accurate than the kit under scrutiny. The values above are for 10% tolerance devices, which is normal and the sort you'd use in a loco. But to avoid 'error stacking' I'd recommend using at most 5% and preferably 2% tolerance resistors in the tester. (IIRC 2% Metal Film/Oxide are fairly readily available.)
I built this one, modified it with a can motor out of an old CD Drive as the motor gives me a better indication of motor performance than the bi-color LED. I had a spare flywheel. I bypassed the large resistor. Green LED for forward light and red LED for reverse light. There are 1k resistors for the LEDs. The decoder being tested is a SoundTraxx DSD steam decoder. Cheap enough tester.
