Get the SoR Robotics Android App on Android Market for FREE. See this forum post for details.
0 Members and 1 Guest are viewing this topic.
I have the same problem with my custom made encoders. On the right side of the robot they work acceptable (I still need to solve some up-down-up counting in some places of the encoder disk). But on the left side, the difference between high and low is so small that the microcontroller does not see it as a change. So I started playing with the resistor values. In my schematic I had both IR LEDs wiren in series with a 220 resistor. But I had to change that and place each LED with it's own resistor in series, with different values. One is 220 and the other is 100 ohms. Also, the 10k pull-up resistor in the colector of the each P.T. has been replaced one with a 4.7k and the other with a 12k. Still, it doesn't work reliably. Probably it's the quality of the disk I made using regular paper and a laser printer. My multimeter has a Digital Signal position that will give me High, Low or in between. By switching to a voltmeter position I have determined that a High signal is over 2.5V and a Low signal is under 0.8V. I have noticed that if the wheels are wobbling a little, the signal is not high or low enough to be seen as a good logic level so that is the reason for my up-down-up counting when the wheels are spinning in the same direction.Conclusion:1. Check with a digital camera if the LEDs are lit. They will be seen as purple dots on the camera screen.2. Place a white piece of paper at 1/4th of an inch distance and replace the series resitor for the LED with a pot and measure the voltage between the P.T. colector and ground while adjusting the pot. When the voltage drops to about 0.5V, disconect the power and measure the pot resistance. Replace the pot with a close value resistor.3. Place a piece of black paper (the real disk will work fine) at the same distance from the sensor and measure the voltage on the P.T. colector (and ground). If it is lower than 2.5V, increase the pull-up resistor. If not, the sensor should work fine.4. The remote test is not allways reliable, since it is a modulated signal. It works for a Panasonic IR detector or something similar like the Sharp or TSOP IR detector.
No, it seems fine.But, are you sure the P.T. is IR sensitive? Measure the resistance when IR light is facing it, it should be lower than 30k. If it isn't, change the pull-up resistors to something like 60k.
The P.T. is IR sensitive, because I am using a QRB1114 package, that has an IR LED and P.T. in one small package. I tried wiring the LED to a 3.3V pwr source through a 220 ohm resistor, and I saw nothing on the camera. When I shined the remote into the camera, I did see the purple light. So could it be that the LED's are burnt out? I tried this on all four of my LEDs, and none of them showed up on the camera.
Also, is it possible for me to just get a ball mouse, and keep the mouse in tact, and use the mouse output someway to get the same effect?
Read this tutorial for selecting the proper resistor value:http://www.societyofrobots.com/schematics_photoresistor.shtml(yea, its a different sensor, but the concept and schematics are the same)Also, a TV remote IR probably isn't the best to use for a test, since its modulated.
the resistance when dark is infinite.
Quotethe resistance when dark is infinite.Impossible. Measure it!(of course, 1 Mohm could be "infinite" relatively . . .)
The 12mA is shared by 4 LEDs which comes to about 3mA per LED. Thats too low.You need to connect individual LEDs independently or use a much lower resistor. Drive the LEDs with at least 50mA of current each.
Now, to the LED resistor size. I have a 300 ohm pot on their power source. I figured 10 mA per LED should be sufficient, so I think about 80 ohms of resistance should be good, with a 5 V power source and 4 - 10mA LEDs. Anyone find a problem with this?
I wanted to know if I could just use one pot to adjust the sensitivity of all four of the sensors. Is this possible?