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3.12. Miniature Receiver with ZN415E (ZN416E) IC The ZN415 IC, being promoted as “The World’s smallest radio” by its
manufacturer (FERRANTI), is an improved version of ZN414. As seen on the
Pic.3.36-a (IC’s block diagram), the 8-pin DIL package contains ZN414 IC
with R1 and R2 resistors, an amplifier with T1 transistor and the separation
stage performed with T2 transistor. All the necessary resistors are
comprised in the IC. Someone will, perhaps, wonder why there are no
capacitors integrated inside, so that the externally mounted parts would
then be only the battery and the headphones? The answer is fairly simple: It
isn’t yet possible to make the capacitors that would have enough big
capacitance, in the monolithic IC’s manufacturing process. Regardless of
this “problem”, the receiver built around the ZN415 is, really, extremely
simple. 3.13. AM Receiver with ZN415E & LM386 IC’s This FRT AM receiver combines the features of two magnificent IC’s,
ZN416E (HF amplifier, detector and the pre-amplifier) and LM386 (audio power
amplifier). Add a power supply based on 7809 voltage stabilizer IC, use a
loudspeaker with membrane diameter being about 15 cm, put all this in one of
the boxes described in the Appendix, and you will have a new and improved
silicone - based model of an old - fashioned radio receiver, built somewhat
less than 100 years ago. The PCB, component layout and connections with other parts of the device ar shown on Pic.3.39. If the receiver is made for the household use, you should certainly put it into some bigger box where bigger loudspeaker (~15 cm) can be installed. The ferrite antenna should be mounted on the rear or side panel, as far from the loudspeaker as possible. All the conductors, especially those that connect the capacitor to the board, should be as short as possible. The wires that connect the loudspeaker and the adapter to the PCB have to be firmly twisted, as shown on picture for the loudspeaker. The potentiometer is to be connected with the shielded microphone cable, if it is more then 10 cm away from the board. A connector for 64-Ohm headphones can also be mounted on the box. It is
then connected to the PCB via a microphone cable, connecting its “live” end
directly on pin No.5, and the shield wire to the closest ground. Headphones
can also be used instead of loudspeaker, in which case such connector must
be chosen, that will switch off the loudspeaker when headphones are plugged
in. 3.14. Miniature receiver with ZN415E & TDA7052 IC’s The 9 V battery is not so popular nowadays as it used to be, probably for
its quite big price/capacity ratio, so it is almost never used in the
pocket-type receivers today. Much more frequently utilized these days are
the cylindrically shaped 1.5 V AA type batteries. Electrical diagram of one
pocket-type AM receiver that uses two of these for power supply is given on
Pic.3.41. Two IC's, ZN415 and TDA7050 are being used in it. The DC supply
voltage for TDA7050 must be exclusively 3 V, and should be no bigger than 4
V. The voltage being supplied from the batteries gets smaller during the
use, but the IC operates properly as long as it doesn't drop below 1.6 V.
Besides this nice feature, this IC has very small dimensions, very low idle
current (4 mA), all the external components it requires are two capacitors
(C8 and C9), which makes it ideal for usage in the mobile-type devices
(radios, wakmans, etc.), the purpose that is originally designated to it by
its manufacturer (Philips).
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