1.5 Volt Tracking Transmitter

The current draw for this tracker is 3.7mA, so the 1.5V button cell will last awhile. What the heck am I suppose to hear you ask? When your circuit is working you should see the LED flash quite fast. Take your FM radio and search for the low-beat ‘humbe-humbe-humbe-etc’ equal to the flash of the LED (probably around the 100Mhz). Found it? If that position is interferering with a radio station you can fine-tune it with the variable capacitor. If you like to have the tracker around the 88Mhz you can do that by spreading the windings from the home-made coil just a bit (1/2 a millimeter or so). Anyways, play with it and learn. It is a nice project. The 12-inch antenna can be anything, it is not really that critical. I used a piece of 22 gauge flexible wire. I haven’t checked the range but will do that shortly.

* For stability, use a NPO types for C2 & C4.
* Resistance tolerance for R1 should be 1 or 2%.
* Frequency range is the usual 87-109Mhz on the FM dial.
* The coil is made from 22 ga ‘hookup’ wire, like the solid Bell phone wire. Leave the insulation on.
* The LED is the ‘High Brightness’ type for maximum illumination.Parts:C1= 100uF electrolytic capacitor
C2= .01uF disc capacitor
C3= 4 to 40 pF trimmer capacitor
C4= 4.7 pF trimmer capacitor
L1= 0.1 uH, 6 to 8 turns of 22 gauge hookup wire close wound around a 1/4″ diameter non-conductive core, such as pencil
IC1= LM3909 LED flasher
Q1= 2N3904 NPN silicon transistor
R1= 10K
Antenna= 10 to 12 inches of hookup wire

One thought on “1.5 Volt Tracking Transmitter

  1. jlg

    The lm3909 ic was one of the most versable chip I have ever see to experimented with. I had  10 pages of notes  on all the experiment  I did with this chip. Spent months missing with the lm3909. The 1.5 volt tracker transmitter will tune above and below 88mz-108mhz be changing the values on the varible capacitor or coil. I put one on the cats where lived to track them for fun. Iever put one on my sister at one time using one of those coin batteries. Used a transitor radio as the reciever. When I worked in a jail system use one as a screamer in the sewer pipe to keep the inmates from using the pipes for a intercom system. I built a IR transmitter that would transmit audio for  about 1000 ft. Lost my notes in a fire many years ago. I wise I had those notes today. Just for fun hook up one of those flashing  LED’s to a coin battery to see how long it will flash. My flashed for 13 months untill it got so dim you was not able to see it in daylight. Here is one that will make people think. Put one those flashing red LED’s in your window so you can see it from outside at night. Looks like you have the cops at your house or inside the house. I am old school  and I say don’t be scared to experiment. That is how u will learn. Computers and electronics ROCK &ROLL. ” SALAM” (PEACE ON TO YOU) . JLG

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