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Daniel Weatherford
hweatherford@silverlink.net
About a month ago, I decided that it would be fun to try and interface Polaroid sonar modules to my robot. Well, I couldn't afford the regular 6500 board, so I went the cheap way. Logging in to EBAY at http://www.ebay.com , I searched under Polaroid Sonar. Two or three of these gems popped up, for only $5 each! I bought three eventually.
After the first one arrived, I started ripping it apart. WARNING - I WAS STEPPING ON CAMERA PIECES FOR WEEKS AFTER DOING ONE OF THESE THINGS!!! I ripped the flash off the top and the film door off the bottom. That should pretty well do it to the camera, there's no turning back. BTW- Keep the flash! Pop it open and look at the size of that capacitor!!! Just remember to use an UNWANTED screwdriver to discharge it... Take a flathead and stick it between the outer shell and faceplate of the camera on the right side and pry really hard. You should feel 2 snaps and it pops out. Do it to the left side, except really low down on the faceplate, so as not to damage the sonar transducer in any way. Now reach up inside the film door and hook your fingers around something and pull and the body of the camera should pop off. Locate the sonar board along the bottom right of the faceplate, somewhat recessed. Rip the clip off that holds it in place and pull the ribbon cable. You won't need it ever again. Then pull the board out of its hole and set it aside. Don't pull too hard on the gray cable, it could disconnect from the board.
The sonar transducer is very easy to remove. Slide it down and to the right as much as you can (looking at front of camera). Then rip off the plastic bar coming out of the top left with wire clippers. Then slide it back up and you should be able to pull it off - I don't exactly remember how it's attached. Remove the gray wire from around the back of the camera, and you're done. If you want to, you can pull the front lens and the mirror in the back - they're nice and high quality.
Warm up your soldering iron. Take wire clippers and find the connector on the sonar board for the ribbon cable. I don't feel like ordering one, so I will make do with what I have. Clip the connector perpendicular to the board between each contact, so you have a bunch of small pieces of plastic to step on. Keep clipping until you can pull all of the plastic off. Then desolder all of the contacts and solder wires to pins 1, 4, 7, and 8 (looking at the board with the chips on the top above the connector, pin 1 is on the left). Take small pieces of spare wire and hook pins 2 and 3 to pin 1. Now, you can connect the sonar board to your system like this:
Pin 1 - GND
Pin 4 - INIT (take high to ping)
Pin 7 - ECHO (Pull up with 47k resistor CONNECTED TO THE SONAR BOARD'S 5Volts!!!
THIS IS
EXTREMELY IMPORTANT!!! - open
collector, will go high with echo)
Pin 8 - +5vDC 2A pulse (Use a 7805 with .1uf caps and a 470+ uf cap hooked to a relay to
power cycle board - BOARD MUST BE POWER CYCLED
BETWEEN PINGS!)
Now to use the sonar board, it's very simple:
1) Don't touch the board. This hurts very much.
2) Don't touch the transducer. This hurts and even if it doesn't it throws off readings.
3) Bring low the INIT line
4) Turn on the relay, powering up the board
5) Wait 300ms (Maybe my relays were horrible so I needed longer to stabilize power -
experiment!)
6) Bring high the INIT line and start counting
7) Stop counting on the rising edge of the ECHO line
8) Bring low the INIT line
9) Turn off the relay, powering down the board
10) Wait 100ms before repeating cycle (Let power supply recover, not needed for beefy
switcher PS's)
Unfortunatly, due to the limitations of this board, I haven't been able to get external blanking signals to work, and jumpering Pins 2 & 3 to ground disables external blanking as it is very sensitive to noise. (Maybe I was just doing something wrong - you ARE supposed to be able to get it to work, though)
Hopefully you won't have the headaches that I did with this board and will get it up and running quickly.