Last Updated on February 28, 2019 by Dave Farquhar
I see a lot of questions about how to wire up circuits, and unfortunately when people ask these questions on train forums, those innocent questions often devolve into heated and unproductive discussions focused on the math and physics involved, or other creative things that overcomplicate the project, and it scares off a number of people, often including the person who asked the question.
Usually what the person asking the question really wants is to not spend a whole Saturday soldering a circuit together, only to find out in the end that it doesn’t work.
So I’ll attack that issue. Here’s how to stage a circuit, find out in a matter of minutes whether it will work, and delay the soldering until you have something promising.
The first step is to find the circuit you want. Often a Google search will turn up a circuit diagram, and if it doesn’t, a Google Books search might. There aren’t very many ideas left that someone, somewhere hasn’t already tried and written about.
Next, gather the components. You’ll probably have to make a trip to Radio Shack. Write down as much about the components as you can, and frankly, before going to Radio Shack, I’d visit their web site, search on the parts you need, and write down the part numbers. Twenty years ago, the Radio Shack sales clerk might have known about electronics components, but today, they specialize in cell phone accessories. But if you bring a list of part numbers, they can usually help you. Or, they may just point you toward the parts drawer and stay out of your way, which is fine, too. The drawers are labeled with ranges of part numbers, so if you end up having to find everything yourself, it’s not too bad.
What you really don’t want is to go in, ask for some resistors, LEDs, and diodes, and be told, “I don’t think we sell that stuff anymore.”
And here’s the big secret. Besides the components, you’ll also want a generous supply of test leads. These are wires with alligator clips on each end. You can get a package of them for around $8 at Radio Shack–they’re part number 278-1156. Or if you live near a Harbor Freight store, you can get a package of 10 for about $3 at Harbor Freight. Be sure to use a coupon. Often you can also get test leads at auto parts stores, though the prices there can vary widely. In a pinch, you can also order them online.
The test leads allow you to build your circuit and experiment with little fear. Just arrange the components and temporarily wire it all together with your test leads, clipping them onto each lead on your components. Double-check everything and make sure you got the polarity right everywhere, then double-check whether the circuit was designed for AC or DC (and add rectifiers if needed). Then when you’re reasonably confident, put on your safety glasses, connect your circuit to a transformer and see if it works. If it doesn’t work, it’s easy enough to troubleshoot. Check polarity again. If you weren’t sure if a resistor went before or after the LED, try it the other way. Keep a notebook handy so you can log the changes you made and draw diagrams if necessary. Or snap pictures of the circuit with a digital camera as you progress.
Since it all just clips together, troubleshooting and rearranging is quick and easy.
As a precaution, wear safety glasses when you’re doing your testing. At low voltages, there’s not a lot that can go wrong and not a lot of danger, but it’s best to take reasonable safety precautions anyway.
Once you get a working circuit, solder it together. You can duplicate the circuit using another set of components, using your clipped-together prototype as a guide. Or you can replace the test leads one at a time with soldered wires, and you can test it at every stage along the way, to make sure your solder joints all work. It’s a matter of personal preference.