Decatur Radar

I got a Decatur Si-2 Radar from Ebay. The brochure that I found online has this as the pinout:

    +12VDC Power           1 (red)
    RS232 TX          2 (black)
    RS232 RX          3 (green)
    Ground(shield)        5 (brown)
    Ground            9 (black)

How should I hookup my Arduino to get the data, and do you think it will be readable?

Edit I also just found this:

It communicates via RS232. It tells the baud rate and serial setup (8 bits, no parity, 1 stop bit). You could connect this directly to a PC and read the data on a serial monitor/terminal. You can even send it requests for data.

Me, I'd put an opto-isolator in the serial line but that's just me.

With an Arduino, some kind of display, a button or two, wiring (and connectors as necessary/desired), resistors, opto, perhaps a small PCB, 12V battery (and casing/box as desired) you can make a nice portable speed gun.

Given that it takes 12V for power, it's likely that you'll need something to convert the signals to the 5V levels your arduino will need. A MAX232 chip is often used for this purpose.

it's likely that you'll need something to convert the signals to the 5V levels

It's RS232 so it is not likely it is certain.

Here's an example of a RS232 to TTL converter.

While reading/writing to the radar will be pretty simple you'll need documentation on the protocol that the radar speaks in order to do anything with it. Without that you'll have to sit down and decode it yourself ... and that won't be fun. Well, not fun to most people. I'd send an email to the people at and ask for protocol details.

How much did you pay for that unit? Looks like it would have been nice for one of my own projects.

An opto-isolator wouldn't handle the signal levels?

So if I were to use a MAX232 what would the schematic need to look like? I know that the radar draws 1A @ 12v.

I found this one, I suppose all I need to modify is to connect pin 1 on the DB9 to +12v? And are those all Electrolytic capacitors?

I'm getting my MAX232 tomorrow in the mail. Just want to make sure this schematic will work...

EDIT: Ardu RX should be on Max 12

Not quite.

Tin is 0/5V level from arduino Tx Rout is 0/5V level to arduino RX

Tout is +/-5V level to RS232 connector Rin is +/-5V level from RS232 connector