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.
As described in project 3.10, the LF signal exits the ZN414. Through the coupling capacitor C3 it is led on the base of T1, and the amplified signal is obtained on its collector pin, and is taken directly on the base pin of T2. The remains of the HF signal are led to the ground over the C4 capacitor. The separation stage allows us to connect small - resistance (64 Ohms) headphones, which are mass - produced these days and are the easiest ones to obtain.
The 1.5 V battery is used for the power supply of the circuit, and is being connected between the pins 6 and 4. Having in mind the previous experience gained with the ZN414 IC, the author recommends to the readers to try improving the signal reception by adding the R2* resistor (helping themselves with linear 1-5 kOhms potentiometer), which is shown in dashed line on the picture.
In the upper end of the Pic.3.37 the table with basic data about ZN415 circuit is given. All these apply on the ZN414 as well, except for the last line. The smaller table given below it contains the data about the DC voltages on the pins of the IC. If something is wrong, the first thing to do is check these voltages and if they are (approximately) as those given in the table, the IC is OK and the error is therefore to be searched in the printings, the contacts, junctions, etc.
Everything that is said about the ferrite antenna in the previous projects applies here as well.
