View Full Version : Boe-Bot using Vex light sensor

08-06-2006, 08:12 AM
I need help. I searched in Vex-land and could not find an answer.

I bought a Vex light sensor to use with my Boe-Bot. The problem is normally the photosensors only have the two leads. The Vex one has the white wire connected to a small board inside the housing. What would the signal wire be for? Is this even useable on a Parallax BS2 board?

I only ask here because I know there is a lot of cross-breeding of robots going on with the discounted parts at Radio Shack.

Thanks for any guidance....

PJ Allen
08-06-2006, 08:33 AM
The leads are probably +V, Ground, and Signal is the output wire.· It's likely an active device, not passive as with a photoresistor.· Apply 5V and measure the output (between signal, the wire in question, and ground) with the device in dark and light.· [It's possible it may have an "open collector" output.]

08-06-2006, 09:08 AM
Ok. Thanks for the help. I just don't want to do anything to fry my BS2. I will answer back when I get results.

PJ Allen
08-06-2006, 09:48 AM
Yep -- people need a power supply (or a voltage source other than their STAMP) to do experiments.· One shouldn't so plumb the unknown with their STAMP, but only apply these unknown quantities after doing·research.

PJ Allen
08-07-2006, 12:34 AM
· Found this PDF for these units:· www.vexlabs.com/docs/inventors-guide/light-sensor-final.pdf (http://www.vexlabs.com/docs/inventors-guide/light-sensor-final.pdf)
· I suspect that they are comprised of a CdS photocell with a fixed resistor, the two in series, so the output/signal in their application will be a voltage that varies with incident light.

· So, I guess that the photocell itself should be between the control/signal lead and one of the other two leads and the fixed resistance should be between the remaining lead and control/signal.· This could be verified easily with a DMM (ohmmeter.)· The easiest application with a STAMP would be to connect the photocell leads to the STAMP as the variable resistance in an·RCTIME·circuit (look that up in PBASIC Help.)

08-07-2006, 07:29 AM
Thanks a lot. I will try to test the circuit you recommended.

PJ Allen
08-07-2006, 09:05 AM
Out of curiosity, I went over to 'the shack' to see if they had any of these, but all they had were a couple of servos, bumper switches (big deal),·limit switches (big deal), and some erector-set stuff like (big yawn).