Hi,
Before pointing out my problem, i will just say that i am very newbie to electronics. Kindly don't offend on my silly questions:
Attached picture is a part of the Sun Tracker sensor based on Red 5mm crystal clear LED. Each LED generate 1.48 VDC when exposed to bright sunlight. The circuit designer has told me to calibrate the sensor with following procedure:
Make both LEDs under bright light and then use the trimpot to get the output voltage zero. I have tried the method, but their is no change on the output voltage with full rotation of 5K pot. I have further explain the circuit in the attached file.
Theoretically the output should change.
What could be a problem is that the led is not able to deliver any current and the impedance of the voltmeter and the low value of the pormeter is causing a measurement fail.
This is just a guess, i have to do the experiment to see what happens.
I am wondering, how do jou want to use this sensor in your project?
The arduino cannot read negative values on it's inputs.
Noorman:
Theoretically the output should change.
What could be a problem is that the led is not able to deliver any current and the impedance of the voltmeter and the low value of the pormeter is causing a measurement fail.
This is just a guess, i have to do the experiment to see what happens.
I am wondering, how do jou want to use this sensor in your project?
The arduino cannot read negative values on it's inputs.
Hi Noorman,
This circuit is nothing to do with Arduino for the time being. This is analogue circuit based on TL082P op-amp. The circuit is not mine, this circuit has been developed by a German engineer Hans. I am attaching the Eagle PCB and schematic.
The Suntracker circuit gets the feedback from the Sensor, based on which it control the two DC motors so that the Solar Panels get to the exact bright spot of the sun. Once the LEDs get equal exposure from the sun the motors stop.
PS:
What value POT should i use to calibrate the sensor?
EDIT:
I delivered your comments to the circuit designer , He gave me fllowing response: [4:08:37 PM] Hans-Juergen Zons: I guess the impedance is OK. Considering a forward voltage of 1.8V and a max forward current of 20mA the LED resistance is 90Ohm. So may a lower value pot would do more.
I don't think the designer understands his own circuit. You need a higher value pot. Each end of the pot goes to each LED and the wiper goes to the voltmeter. With a lower pot value you cause more current to flow and there really isn't a lot of current to spare in this circuit.
I don't think the designer understands his own circuit. You need a higher value pot. Each end of the pot goes to each LED and the wiper goes to the voltmeter. With a lower pot value you cause more current to flow and there really isn't a lot of current to spare in this circuit.
Hi Mike.. thank you for taking interest in this problem. You are right as i have already did experiment replacing the 5K pot with 1K pot with no-positive results:(... Is their anyway to calculate the pot value to be effectively use here?.. Electronics is not a guess work, its a science;) So i need help from you guys that are master in this science.. Can anybody simulate/calculate the POT for me?
LEDs connected in reverse, it's mean that one generate + 1.48V another generate -1.48V, if both of them exposed to the light output is must be zero. Meaning of the pot, is adjust zero volts output, which vouldn't be exact due small mismatch in voltage from two leds ( +- 0.02V or so).
If you measure 1.48 when two leds under lights, you made mistake with polarity of one led or another.
Magician:
LEDs connected in reverse, it's mean that one generate + 1.48V another generate -1.48V, if both of them exposed to the light output is must be zero. Meaning of the pot, is adjust zero volts output, which vouldn't be exact due small mismatch in voltage from two leds ( +- 0.02V or so).
If you measure 1.48 when two leds under lights, you made mistake with polarity of one led or another.
Hi ,
SOrry, i might have some different opinion;) If i remove the POT and combine the output of both LED i will never get 0 or near to zero voltage;)
I didn't say remove a pot. A resistor is a load, the higher value the more disbalanse voltage you can register. In other words higher value is preferable, limited only input impedance of the measurement circuitry, 5K is better than 1K.
Did you find you faults in polarity?
Magician:
I didn't say remove a pot. A resistor is a load, the higher value the more disbalanse voltage you can register. In other words higher value is preferable, limited only input impedance of the measurement circuitry, 5K is better than 1K.
Did you find you faults in polarity?
IMHO, removing or not removing the POT does not make any difference.. Just think we are playing with LED.. So in LED the last alphabit is 'D' that mean Diode.. so the overall voltage will never cancel out i.e. i will always get voltage generated by one LED (+1.48 VDC)
yes i check the polarity and its right.
I can think of a few possible explanations for the fault:
the two LEDs are connected the same way round instead of opposite ways round
the two LEDs are not the same type
bad solder joint on one of the LEDs or one end of the pot
faulty led
faulty pot
I suggest you measure the voltage from the LED common connection to the other connection of each LED in turn. In bight light, one should give you a positive voltage, the other a negative voltage.
The culprit was the bad installation of LED.. This not means that i have installed the LEDs wrong way. The attached picture will clear what was happening. Actually the leds legs having notches that can not go inside the drill hole so i soldered the LEDs keeping the notches above the PCB. This made the LEDs 3mm above the PCB. The LED was disoriented i.e. The LED base was not square to the PCB and tilted. Hence, although i aligned perfectly the LEDS with the sun i was getting +1.48 volts.(because the LEDs face towards the sun were not centered )
Actually what i did was to remove all LEDs .. Removed the long length of legs removed the notches.. and made the Led bottom flush with the PCB.. This way all LEDs lens direction become same and the LEDs are square to the PCB.. Now using artificial 1watt LED lamp i found that i can get ZERO voltage when the LEDS get equal exposure of light...
