Servo - June 2008

building your own may be a lot more fun. It is for me.

Electronics

This is the area I enjoy the most and I wanted to use some of the boards we sell at BeginnerElectronics.com, but also make this article something for more than just our customers. I wanted to make this into a robot platform that worked with various electronic control boards. I originally planned to use one of our Ultimate OEM boards originally designed by Chuck Hellebuyck of elproducts.com since it has a common input/output (I/O) pin-out that matches many similar OEM-style boards. The original Basic Atom OEM board and the Parallax BASIC Stamp OEM boards share the same 20-pin header layout. The Ultimate OEM takes that further by bringing the extra I/O out to the main header to offer more direct I/O. Each of these OEM modules has their own options for programming. The Basic Atom OEM module shown in Figure 2 is the one I chose to use in this project and is programmable using the BasicMicro.com Basic compiler that you can download for free from their website.

The Atom OEM software uses the same Basic language type commands as the Stamp but offers faster operation and more memory for program and variables. The Atom has analog-to-digital (A/D) ports built in that are brought out to the AX0,1,2 and 4 holes at the top of the board. If I wanted something beyond BASIC, I could have used the Ultimate OEM module which can be configured as an Atom or used with a bootloader PIC so it can be programmed with PICBASIC PRO, a C Compiler or even assembly language. The Ultimate OEM also has an in-circuit programming port at the top so you can program it directly from a PIC programmer. This allows you to use a blank PIC rather than a bootloader chip. If you are partial to the BASIC Stamp, then a BS2 OEM will work fine with this project, as well. The point is they all share the same first 20 pins at their main I/O headers which allows them to share a common connection footprint.

Docking Station

FIGURE 3. Silkscreen layer.

FIGURE 4. Bottom layer.

FIGURE 5. Top layer.

The OEM docking station also has all the module I/O pins brought out to three pin connectors, including the extra pins that the Ultimate OEM has. The three pin headers have one pin connected to an I/O while the other two are power and ground. The central power bus line is actually split into two lines with each connected to a different power switch. The pins that are within the silkscreen that says “servo” are the pins that have power controlled by the servo power switch. The rest are controlled by the other power switch. This is how you can shut off the servos and keep power to the electronics.

Many sensors have three pin connectors similar to a

We modified a custom board design originally developed at elproducts.com to make a base for the OEM modules to plug into. Because all the OEM modules share the same first 20 pins, making a common OEM docking board that will work with any of them is easy. The board layout is shown in Figures 3, 4, and 5. The board was created with ExpressPCB free layout software and you can download this file from the BeginnerElectronics.com website.

The docking station is designed for robotics as it has separate power inputs for servos and module power. Each power input also has its own on/off switch so you can switch off the servo power but still have power applied to your OEM module. This allows you to program the OEM module without the possibility of having the servos driving the robot off your bench. When you are ready to put your robot on the floor to test it, then you can flip the servo switch to “on” to let the servos run.