Table 15-2
Capacitance code information
This table provides the value of alphanumeric coded ceramic, mylar and mica capacitors in general. They come in many sizes, shapes, values and ratings; many different manufacturers worldwide produce them and not all play by the same rules. Some capacitors actually have the numeric values stamped on them; however, many are color coded and some have alphanumeric codes. The capacitor’s first and second significant number IDs are the first and second values, followed by the multiplier number code, followed by the percentage tolerance letter code. Usually the first two digits of the code represent the significant part of the value, while the third digit, called the multiplier, corresponds to the number of zeros to be added to the first two digits.
Value Type Code Value Type Code
1.5 pF Ceramic 1,000 pF /.001 µF Ceramic / Mylar 102 3.3 pF Ceramic 1,500 pF /.0015 µF Ceramic / Mylar 152 10 pF Ceramic 2,000 pF /.002 µF Ceramic / Mylar 202 15 pF Ceramic 2,200 pF /.0022 µF Ceramic / Mylar 222 20 pF Ceramic 4,700 pF /.0047 µF Ceramic / Mylar 472 30 pF Ceramic 5,000 pF /.005 µF Ceramic / Mylar 502 33 pF Ceramic 5,600 pF /.0056 µF Ceramic / Mylar 562 47 pF Ceramic 6,800 pF /.0068 µF Ceramic / Mylar 682 56 pF Ceramic .01 Ceramic / Mylar 103 68 pF Ceramic .015 Mylar 75 pF Ceramic .02 Mylar 203 82 pF Ceramic .022 Mylar 223 91 pF Ceramic .033 Mylar 333 100 pF Ceramic 101 .047 Mylar 473 120 pF Ceramic 121 .05 Mylar 503 130 pF Ceramic 131 .056 Mylar 563 150 pF Ceramic 151 .068 Mylar 683 180 pF Ceramic 181 .1 Mylar 104 220 pF Ceramic 221 .2 Mylar 204 330 pF Ceramic 331 .22 Mylar 224 470 pF Ceramic 471 .33 Mylar 334 560 pF Ceramic 561 .47 Mylar 474 680 pF Ceramic 681 .56 Mylar 564 750 pF Ceramic 751 1 Mylar 105 820 pF Ceramic 821 2 Mylar 205 1st Significant Figure 2nd Significant Figure Multiplier Tolerance CSGNetwork.Com 6/4/92 0.1µF 10% 104 k
should remove the solder from the joint and re-solder the connection point over again until it looks good. Next we will inspect the PC board for any possible “short” circuits which may be the result of “stray” component leads which may have stuck to the foil side of the PC board. These “stray” components leads often “stick” to the board by solder residue. Solder blobs are often a cause of “short” circuits, so look the board over carefully for any solder blobs as well. Once the circuit board has been inspected, we can move on to installing the circuit board into a case or enclosure.
We mounted the induction loop receiver in a 3′′ ×6′′ by 11/2′′metal chassis box. We placed one 1/8′′jack at
the rear of the case for coil L1, then we placed the second1/4′′phone jack, power on-off switch and volume
control on the front side of the chassis box. Locate a 9 volt battery clip and solder the black or minus (−) lead to the circuit ground. Next you will want to wire the red or positive (+) battery clip in series with the On-Off switch to the two power junction points on the PC board, one at R2 and the other at pin 6 of the LM386 IC. Once the circuit is inside the enclosure, you can begin testing the induction loop system. First you will want to make sure that the “transmitter” portion of the system is up and running. If you elected to use an existing stereo receiver or amplifier, make sure that the large coil is connected through a series resistor to the speaker terminals of the amplifier. Set the receiver or amplifier to MONO. If you elected to build your own audio amplifier to drive the large loop, again connect up the coil via an 8 ohm 10 watt series resistor. Once the
“transmitter” is ready, with your music or audio source connected, we can move on to testing the induction loop receiver.
Switch the induction receiver to the “On” position. When you first turn on the unit you will probably hear a lot of buzzing from the wiring in the room. Rotate the receiver in a horizontal plane to find a “null” where the hum is minimal. If you can get a reasonable null, you should be able to hear the source material from the “transmitter” loop or at least some hum coming from the earphone. If your “transmitter” loop is “broadcasting” then you should hear the source music or speech on the headphone of your induction loop receiver. If all goes well, both your transmitter and receiver section will be working and you will be hearing the source material in your remote headphones.
In the event that the induction receiver does not work when first power-up, you will have to remove the battery and carefully examine the circuit board for any errors. The most common cause for failure are improper placement of resistors, electrolytic capacitors and diodes installed backwards, and semiconductors such as transistors installed incorrectly. Have a knowledgeable electronics friend provide a second pair-of-eyes to help you examine the circuit for errors. It is very easy to miss a problem since, as the builder, you will continue to see the same circuit, the same way over and over. Once the error has been found and corrected, you can re-connect the battery and test the circuit once again.
As mentioned earlier, you can use the system for hard of hearing people, for museum displays and demonstrations, for theater personnel, late night TV listening, etc. You could wind a transmitter loop around your easy chair and use the system to “broadcast” TV sound to your earphones for late night listening. This is a great Boy Scout project for helping old folks
who live in nursing homes to better enjoy TV, radio and music.
You can also use the induction loop receiver by itself without the transmitter loop, to trace power wires behind a wall or ceiling by listening for a sharp increase in hum as the coil passes near the wire. Make sure that current is flowing in the wires to be traced by turning on a lamp or other appliance. Other wires can be traced if they are carrying alternating current in the audio
Chapter Fifteen: Induction Loop Receiving System
EBC BC548 NTE123AP LM386 1 8 1 2 3 4 8 7 6 5 LM2002 +IN V s V out end −IN
range or a signal generator can be connected to produce the current. Connect the generator to the wire to be traced and connect the generator’s “ground” to the house wiring ground. Also ground the far end of the wire you are tracing so that current flows in
the wire. This ground connection can also just be a temporary wire laying on the floor running from the generator ground to the far end of the wire you wish to trace. Have fun using your new induction loop receiver!