Hi friends, am back, the last update was Oct. 7. It's the 18th. We will have to squeeze in a side topic for some students in Zambales  It's on MODULATED IR.


MODULATED IR

     Usually, when working with IR, ambient light is a problem. At the other end, usually a photo transistor is used. One solution is to house the photo transistor in a straight tube, say 6 inches. Only a straight beam can enter when it is aligned with the tube. The other way is to modulate the IR at about 1 khz using a 555 timer IC. Then the photo transistor is fed into an LM567 frequency decoder. The tube may still be used in addition. I will post the schematic later.

BK


Back to our main topic, OSCILLATOR.

     Hmmmmm, let's see. What can we build to learn about oscillators?. Answer: A Walike-Talkie! A WT is just a pair of units which has a TX and an RX in each unit. In short, the TX and RX are just duplicated. WE DONT HAVE TO BUILD BOTH for learning. We build one each, ok?

     Which one first? If we build the RX, we have no TX to test it with. If we build the TX, we have no RX to test it with. It's the Chicken and Egg Paradox! But wait a minute, we can build a very simple RF detector which will tell us if the TX is putting out signals.


     THE RF PROBE:

             JUST GET TWO IN4148 DIODES. JOIN THE PLUS END TO THE MINUS END OF THE OTHER DIODE. CONNECT THE OPEN ENDS TO YOU VOLTMETER SET TO THE LOWEST VOLTAGE RANGE. OR IF YOU HAVE VU METER, CONNECT TO THE VU METER. THE PLUS OF THE DIODE SHOULD GO TO THE RED PROBE OF YOUR METER. THE VU HAS A PLUS AND MINUS MARKING TOO. SOLDER A PIECE OF WIRE SAY 6 INCHES LONG to the joint ends of the diodes AND PUT A TINY ALLIGATOR CLIP. DONE. YOU NOW HAVE AN RF DETECTOR .

     If you have a toy transmitter, touch the clip to the antenna and press transmit. See the needle jump?

THE TRANSMITTER IS AN OSCILLATOR


     (to follow since I will have to scan a schematic diagram)