Step 4: Building the circuit

Picture of Building the circuit
You need to create a coil that's about 150 to about 162 uH (different sources say it should be different values).  To determine how many winds to do you can use an induction calculator like the one here www.crystalradio.net/cal/indcal2.shtml.  I used the green spool from the Radio Shack set of wires and wound it about 133 times around the toilet paper roll (I did this both by working with a calculator and some trial and error, I have no tuning equipment).  You probably want to leave a little extra wire in case you need to wind some more to get your antenna tuned right.

After you have your coil you can connect it to your circuit.  The schematic is pretty easy.  Just connect pin 9 on the Arudino to a 10 K Ohm resistor, then to the base of the transistor.  Next you can put your capacitor between the collector and emitter of the transistor.  The emitter also needs to be connected to ground.  Next connect the coil the the emitter and collector of the transistor.
Is it possible to replace the coil by an inductor of the same inductance? It has the same effects?
flashmandv4 years ago
do we have to change the circuit if we want to use bi-phase coding ?
musick74 years ago
Here is a Link for a Simple Meter that will help with this Process. It's an LC Meter it will Read VERY SMALL Amounts.
If you need to MAKE YOUR OWN COIL then this is the Meter for you.
Simple to Build Schematic and Instructions are located here: