PBP projects for R/C models

[Kenjones1935]

How's this sound. Two 100 watt bulbs inside reflectors. One mounted close to the beginning of the maze and the other at the end of the maze. I think I could get a standard photocell to detect the difference between that light intensity and ambient room level. The rule for the PIC would be, "See the light, TOGGLE."

Here's the spec for the PHILMORE photocell 10807:

"A typical use is for switching on lighting after dark. These are also used in alarm systems, exposure meters, flame detectors, opto-couplers etc. This cell has a dark resistance of 5,000 ohms and 300 ohms in bright light (100 cds. or more)."

If this technique were used in my car an emergency TOGGLE device would be a powerful flashlight.

What do you think? I have the 10807's. I think I need to experiment. An old fashioned Triplett multimeter should to the trick.

On the old subject of oscillations. These were oscillations in the motion of the car. They were caused by my not correctly selecting the thresholds on the SRF05 proximity detectors. I felt I solved that.

The idea of a WHILE WEND loop is a good one. I sort of do that already. The PIC triggers the SRF05's many many times per second. My car continues to do one thing until the three echo pattern changes, then it does something else. If there is a bit of noise in one set of readings, it is smoothed over by the next set coming in a few milliseconds. I do not have an error signal.

When I first read Ioannis' PID suggestion I thought of a PID system based on position of the servo. My mistake. He is really suggesting that I devise an error signal to minimize. I gotta think more about that.

Ken

[mackrackit]

The photocell should work, not sending data, just a simple HIGH/LOW..

Just in case you do not have the link.
http://www.picbasic.co.uk/forum/showthread.php?t=5874

[Kenjones1935]

I'm not getting my analog voltage comparator act together.

I want the teacher, at race time, to certify that each car will respond correctly to the bright lights at the beginning and end of the maze.
The photoresister R/C to PIC toggling threshold should be calibrated per car.

The PICkit2 comes with a built in pot attached to pin RA0. Each car while being exposed to the bright light could have its pot turned with a long handled screw driver (avoiding shadows) to the point that the car's control toggles.

This translates to a voltage comparison between the input of RA0 and RA1. The photoresister 10807 reduces its resistance in bright light from 5k down to near 500 ohms If I build a voltage divider with a 5k resistor to Vss = 5V and the 10807 to Gnd and attach it to RA1 will that do the trick? It would give the PIC a swing of about 2V not figuring the input impedance of the PIC.

I've got a some of questions.

First, does the above make sense?
Second, do any of you know some PBP code that does a similar comparison?
Three, I believe I will need to smooth out noise during the transition as the car comes into and leaves the bright light? How would you suggest I do that?

Ken

[mackrackit]

First, does the above make sense?

Yes.

Second, do any of you know some PBP code that does a similar comparison?

I do not have any code but here is how I might try setting it up.
First add a switch on the car and code for the switch at power-up. Also add a LED for calibration indicator.
If switch is HIGH then ADC_SETUP routine. The code will go here once and never loop back to it.
Inside the SET_UP routine have the drive wheels turned off and sub loop reading the ADC from the light and the "calibration" pot.
Have it coded so when the reading from the light and pot are equal with in a certain amount (exact will be difficult) the calibration LED come on.
Then when the calibration switch is turned off the code will go to EXIT_SETUP. This routine will save the ADC reading from the pot to EEPROM then goto the main program.
Now the main program will read the EEPROM to get the value to use for light checking. The reason for EEPROM writing is you will only have to "setup" once and not have to do the setup every time the car is turned on. Maze changes do another SET_UP.

Three, I believe I will need to smooth out noise during the transition as the car comes into and leaves the bright light? How would you suggest I do that?

Turn to the students and say "SSHHH"

Are you meaning light noise? If so this is where the ADC needs to be with in a certain amount so a small range of "bright" light will do the triggering. This partwill take some experimentation for car speed and othe on site variables.

[Kenjones1935]

I took the car to a TV studio today. It was going to be on Access television. I brought the laptop computer and the USB connector. I forgot the battery charger. The car had not been charged for a couple of days. Big mistake.

At the beginning it did just as I thought I had told it, but then as time went on it crashed more, got stuck more. I chose not to do the TV shoot. It sort of worked, but not quite.

I think as the battery discharges, even with the 5volt voltage regulator in the electronic speed control box, everything degrades before it finally refuses to move. I know the DC wheel power motor uses lots of juice

Sound correct to you all?

Ken

[mackrackit]

Sounds correct to me. When the voltage drops below a certain point all kinds of strange things can happen. The PIC ® is probably running "OK" at 8Mhz, but the 5 volt peripherals are probably not happy.

[malc-c]

To be honest I would never use the same power pack to power the electronics. Even when using electric helicopters I would use an RC pack for the receiver, with the main flight pack used just for driving the main motor. 4 x 1.2v Nicads provides a decent supply for the electronics