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). * Caution must be expressed with the power supply, since this two-batteries power supply cannot be simply replaced with some common-type 3V adaptor. If you wish to use such adaptor, the pin 6 of ZN414 must be connected, over the R2 resistor and one of the circuits from Pic.3.35, to the pin 8 of the TDA7050, and the adaptor is then to be connected between the pin 8 and the ground.* The R2* resistor, shown in dashed line on the picture, should be added only if the receiver does not operate stable. Determining its exact value is explained in several previous projects.* The 64 Ohm headphones are connected onto the output of the ZN415 (between pin 5 and Gnd), or instead of the loudspeaker (in which case the reproduction can be much louder).* The PCB and components layout is shown on the Pic.3.42. Connecting other components is being done in the similar manner as in the previous project. In the left corner the batteries are shown, placed in some convenient holder taken from some old device. Between the plus pole of the left and the minus pole of the right battery the tin plate is inserted, with one of 3 cables connecting the supply to the PCB soldered to it.