Servo - November 2011

www.servomagazine.com/index.php?/magazine/article/november2011_MrRoboto

not intended to be a tutorial, so there are perhaps (ahem) a few holes ...

Your first question on “how to tell the boards apart” is right on. You have to look at them to tell. There is no information other than our posted pictures. Fortunately, they do look distinct enough that examination works fine. The very oldest of the Polaroid sonar boards is the “One Step.” That board looks even older with its odd configuration. This board is the hardest to hack because you need to cut traces to keep it from doing things that worked fine in the camera (working the focus), but that you don’t want to happen in your robot. We hijack some of these pins for our own use. The Sun 660 and 660 One Step look similar, but upon inspection, are very different. The most obvious difference is the existence of “C63,” a trimmer cap on the newer Sun 660 boards (see Figure 3).

My notes are clear on how to install the reservoir capacitor on these two boards, except perhaps about where the - and + leads go. So, let me answer that question next. My notes clearly label these leads, but on the older 660 One Step it may not be clear how to attach them. Look at Figure 4; the + side of this large capacitor is on the right. If you have this old 660 One Step board oriented as I show, you will see a bare wire on the top side of the board, running horizontally under the black choke. Solder the + lead of the cap to this wire. Somewhat more difficult to see from a picture is the bare wire on the top side of the board running vertically alongside the connector. This is a ground wire; solder the - side of the capacitor to this wire.

Because the connector on this board is not something that easily matches any connector that I ever had, I removed it so that I could solder wires directly to the board to handle the power switching and signal inputs and outputs that I wanted.

This leads us to the third question; the one about “J1.” Because there really isn’t any documentation about this board — at least none available over a decade after the camera ceased production — we are left on our own to determine how to label the connector. I used the label orientation that Polaroid used on its 6500 sonar experimenter boards (also obsolete shortly after I discovered them). It wasn’t a perfect match; the 6500 J1 had more pins, for instance, but the pin description matched up to pin 8. I don’t know what decided

Circuit Cellar’s pin orientation for J1. If you look at the two, you’ll

Figure 2. Polaroid One Step sonar board.

see that the pins are simply mirrored. My pin 8 is V+ which has the transistor attached to it so that the microcontroller can turn the power on and off to the board at will to reset it. By the way, the collector is tied to pin 8, not the base of the transistor. I use a PNP transistor to handle this because the large capacitor I use as an energy reservoir can be charged easily with the TO92 transistor when the board is powered on. Its large value can supply the high current spike caused when the board triggers its sonar pulse without disturbing the microcontroller.