Introduction of Robotics

Here Sachin Maurya a mechanical Engineer shares his ideas about ROBOTICS

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Sunday, January 13, 2008

The Techniques of connection

Introduction

While building a robot you need to connect multiple devices together. There are lots of ways to connect them. Some are better than others!
I have built lots off things that turn into a real rats nest. I would need one thing connected to my power source so I just solder a wire to the positive side and another wire to the ground side. As Chef Tell would say "Very simple, very easy". Then I needed a second device so I soldered those wires on. It's still not bad, yet... Or you can just twist the wires together, solder them and cover it with tape...
As you add more devices it becomes a real problem!

The picture on the left shows multiple wires soldered to a common point. It's not obvious from this picture but one of the red wires is soldered to another common point on the back of the board. And it has another 2 or 3 wires soldered to it. Both photos show examples of multiple wires soldered together and covered with tape.

Connections will generally fall into one of two categories:

Individual signals
Bussed or grouped signals

I will present different methods to make these connections.

Individual Connections

There are various ways to make a single connection. The following techniques come to mind:

Solder
Banana plugs and jacks
Jumper wires
Wire-Wrap
Screw terminals
Block pin connectors
Pin connectors
Combination pin/screw connectors
COAX cable connectors

Solder Connections

As simple way to attach a wire is to solder it to a pin. This is a good way to permanently attach a wire. For instance, you may want to solder wires directly to a motor. Then use a quick-disconnect on the other end of the wires.

These photos show different devices with soldered connections. The first one shows a voltage regulator which is bolted to a heat sink. The second one shows wires and a capacitor soldered to motor terminals. The third one shows wires soldered directly to a PC board. Just keep in mind these are permanent connections.

Banana plugs and jacks

Jumper wires

Wire-Wrap

Wire-wrap has been around a long time. Basically you have square pins and wire is wrapped around a pin to make the connection. Wire-wrap sockets are available for standard DIP I.C. packages. If you look around you can also find other types of sockets available.
You can connect two boards together with wire-wrap wire. But the standard 30 gauge wire is made from steel (or iron) and is more brittle than copper wire. This leads to the wire breaking if it is flexed much. So it is best to have the boards mounted solidly if using 30 gauge wire-wrap wire to connect them.
The actual connection is made using a wire-wrap tool. It looks much like a screwdriver. It has two holes in the business end. One in the center which slides over the pin to be wrapped. The other hole is offset from the center. The wire to be applied is slipped into this second hole. As the tool is turned the wire wraps itself around the pin.
You can also find power wire-wrap guns. They are electric or pneumatic. But for occasional use the hand operated wire-wrap tool is adequate.
Back when I did a lot of wire-wrapping I was amazed that it usually cost more for the socket than for the I.C. Over the years I have collected wire-wrap sockets when I found them at a cheap price.

Screw terminals

Screw terminals can be handy. They come in various sizes. You can get PC mount type and also simple terminal blocks you connect multiple wires to. The smaller PC mount types are designed to have a wire inserted and screwed down. The larger type work well with a crimp-on connector.

If you use stranded wire with a screw terminal I recommend tinning the wiring with solder before connecting it to the screw terminal. This prevents the individual wire strands from fraying and possibly causing a short.

Even though the terminal blocks (as seen in the first photo) are very handy, they seem to take up a lot of valuable space. My robot projects are usually quite large so it isn't a big problem for me. They are available in smaller screw sizes also.

Crimp-on terminals

Crimp-on terminals provide an easy way to terminate individual wires. This provides a clean connection to a screw terminal. The terminals come in a variety of sizes and types. They are applied using a crimper. You can get "cheap" crimpers at auto supply stores and hardware stores. They work, but not very well. (In my humble opinion) The high quality yellow handle crimpers in the picture are a pair I picked up at a swap meet for 4000 Rs. A pair from AMP or other major brands seems to run around 3200 Rs for some unknown reason...
The terminals are available at Radio Shack, auto supply, hardware and lots of other stores.

Block pin connectors

This type of connector allows an easy way to make a cable removable. You can cut the cable and install this in between the two ends. These are available at Radio Shack and most electronics suppliers. (Maybe even auto parts stores) They come in at least two different pin sizes. Right off hand I know you can get them with pins ranging from 2 to 12, maybe bigger.

PCB pin connectors

Pin connectors provide a very flexible way to terminate your wires. They come in two basic types. Single wires and multiple wires (like ribbon cable). The multiple connections are presented on the next page. I use two different size of connectors.
The smaller, red ones are Molex/Weld There are many, inexpensive ways to lay out the electronic components which interface to your Stamp board. A good layout has the following features:

1. All components are secured to some kind of rigid backing. Nothing is flopping in the breeze.

2. Wires are only as long as they need be. No wire loops rising above the board.

3. Component leads are trimmed so that there is no danger of leads shorting should they be bent.

4. The entire project, including batteries, can be lifted with one hand. Everything is one backing board.

5. The project can survive modest drops and modest shaking without connections coming loose.

6. All motor housings are secured so that the housing doesn't move when the motor is powered.

7. Switches are anchored so that they can be operated with one hand.

Here are some pictures of circuits which interface an LED, a small motor and a switch to the Stamp. Use them for ideas. on connectors. The pins are .1" on center so they fit in standard perf board. I get them from Digit Key. You buy the pin blocks, socket blocks and pins separately. They come in lots of sizes so you pick the size you need for the application. (Some times it is good to have all the connectors on a board be different sizes. Then you can't plug the wrong one in by mistake.) You can get a crimper for the socket pins, but I can't find mine at the moment. I usually solder the pin whither I crimp it or attach it by hand. I've had too many come loose if I don't solder them.
The other types have the pin permanently mounted in the socket block. You crimp the wire into the socket itself. These come in at least two different sizes. I have .1" and .156" pin spacing sizes. The larger size are rated at around 3 to 5 amps. They are made by AMP and Pundit and others. I managed to find a pistol crimper for the large and small ones and surplus stores. (These are something else that cost too much when they are new. I think they are over $100. :-O ) I also found a hand crimper which you can see in the photo.

AMP MT pin connectors

This is another type of pin connector. They come as single in-line or dual in-line. They are end and edge stackable. (Which means you can insert them side-by-side.) So you can mix and match them on a larger block of connector pins.

Combination pin/screw connectors

A pin/screw connector offers an interesting alternative. It allows individual wires to be attached at random since each pin has a screw terminal. It also allows the whole connector block to be pulled off the pins when removing the board. (Note: I didn't have the pin block handy for the photo.)

COAX cable connectors

There are various ways to terminate COAX cable. COAX stands for Co-Axial. A COAX cable has a central wire surrounded by a concentric shield wire. COAX is usually used for analog or RF signals. You can use RCA phonon connectors, BNC connectors and lots of other types.