FM Radio Receiver Using TDA7088

Home Electronic Store Electronic Blog Electronic Schematics Tutorials Downloads Contact FM Radio Receiver using TDA7088 FM Radio Receiver using TDA7088 This tiny receiver is not much bigger than an AA cell. It is powered off two LR44 button cells, which are expensive and I assume wouldn't last terribly long. I'll be on the lookout for LR44's at the markets and $2 shops now that I've got this radio! As with all these sorts of radios, the headphone lead functions as the aerial. Supplied with this receiver were a pair of those awful "intheear" type of miniature type earphones. Apart from the appalling sound quality, they are insensitive, unhygenic and dirty, fragile, and do not block out external sounds. So, I use the normal kind of headphones instead. The enclosure is all clipped together, and once I'd opened it, sure enough, a TDA7088T was visible. The audio amp appears to be one transistor; ie. single ended class A. I don't know what current it's drawing so I can't say whether it's consuming much more battery current than a class B amp would. In any case I would prefer AAA cells rather than the LR44's. since the voltmeter that has the scale that is big enough takes too much space.12 with an audio receiver made with LM386 IC. therefore if using a 4. as there is only one tuned circuit (i. Maximum value of the DC supply voltage for the TDA7088T is 5V. This problem can be solved by adding a small voltmeter in parallel to the BB909. Sound quality is good. which is loaded by cheap 16Ohm headphones.The power switch is a minature slide switch on the side. This is obviously done to avoid a space consuming potentiometer. the ferrite loopstick).3. the D2 diode and C15 capacitor should be omitted.8. and R4 should be shortcircuited. however. in order to cover the entire reception bandwidth.11. They're a strictly "local station only" affair as far as AM goes. which has an extra position for volume. However. Most of them use the Chinese clone of the TDA7088; the SC1088.8. .5 V battery the LM386 will work with reduced output power. As one can see. It is most simple to use numbers from 1 to 10. Electronic diagram of such receiver made with TDA7088T is given on Pic.4. Once you have reached the 108Mc/s limit. It is in this case better using a manual tuning instead of automatic. whose scale is graduated in MHz.4. and you certainly shouldn't pay more than $5 for one. as on Pic.4. The AFC (Automatic Frequency Control) of the local oscillator is accomplished with BA483 diode. The tuning is done via the variable capacitor C with numbers written on its button. The telescopic antenna is used. Such solution is given on Pic.13. The variable capacitor is like the one on Pic. the headphone lead aerial is not as efficient as a 75cm telescopic aerial so this needs to be taken into account. as described in the Appendix. Unfortunately. that is a receiver from Pic. The complete radio receiver should still have a loudspeaker. Some also incorporate an AM receiver. The operating principle of this device is given in the previous chapter. The only thing new is a very simple audio amplifier made with BC547 transistor. on both AM and FM. AM sensitivity is poor because of the very small ferrite loopstick aerial. the TDA7088 has the mute permanently enabled so some weaker stations that could otherwise be received with a TDA7000 or TDA7010T cannot be received on the TDA7088T. Variable condenser tuning is used with these sets.4. Performance is the same as the TDA7000 IC in terms of sensitivity and sound quality.e.14. It does not automatically do this like a PLL type of circuit would.4. these cheap auto scan FM receivers also incorporate a torch. So.4. This invariably uses a TRF circuit based around an MK484 (ZN414). you have to press "reset" to get back to the 88Mc/s end of the band. The electronic diagram of the monophonic FM receiver made with TDA7088T is shown on Pic. Some experimenting is to be done with capacitances of Cx and Cy. More often than not. we have only two levels of volume; full and something a bit less. If built with SMD components it can be placed in a matchbox. The scanning circuit works very well. altogether with two buttontype batteries. These TDA7088 receivers are very common in $2 shops (look for the "scan" & "reset" buttons). from 88 till 108 MHz. This solution is not appropriate for the miniature receiver. Also. similar to that on Pic. there is virtually no waiting for the radio to find the next occupied frequency. Small mishap of this receiver is that it has no indication of station tuning.12. obtaining that station’s position on scale does not “walk” over the scale. How well does it work? Quite well actually. The firs legs to be soldered are the diagonally opposite ones. Any other .15b. Soldering the pin No.15b contains the PCB component side layout. shows the PCB for the HF part of the receiver with TDA7088T. D2 is a Zener diode with 3 V Zener voltage. Once again you have to check whether all the pins are properly placed. That is why it is being drawn in dashed line on pic. the voltage stabilizer. until the optimum value is found). The IC is placed in its position. Pin No. * Pic. so that both of them are heated. type BO2AMAP2. The tin gets melted. and if not smaller one.9 is shown on Pic.4. in order not to overheat the pin. The soldering procedure for SMD is as follows: A thin tin layer is applied on the copper contacts where IC legs are to be soldered to. where the board layout on the component side is given. directly onto the copper contacts. The tip of the tinol wire is then approached to touch the iron. instead of the SMD’s. one of which is being used by this device.4. The TDA is soldered on the copper side. R4=1. while simultaneously keeping the voltage on Pin 4 about 3 V and the device working well within the entire reception bandwidth (One should start with. so it has to be constantly moved downwards. After app. Pic.4. The wire gets melted and adheres to the copper and the pin.1 is pressed against the tin pillow with a top of a bodkin. The optimum value of R4 is found experimentally: in order to make the power consumption as low as possible it should have the resistance as big as possible. the pin top and the copper contact at the same time. and then they too are soldered as it was just described.4.15a shows the board layout from the soldering (copper) side.4. The pushbuttons we used here are Siemens.If higher voltage battery is used. as one can see. It is now time to check out the positioning of the chip. A small cushionshaped amount of tin (not profuse) is applied on the contacts where these pins are to be soldered (pic. that is realized with ordinary components.5 kOhm. has to be activated. with all the pins properly laid.17a). the iron is slightly removed from the leg but remains on the copper contact. First. When enough tin is applied.4. two button switches. then the iron. the tin surrounding the pin No. The common housing contains.1 is melted with iron tip and the chip position is quickly and carefully adjusted. in this case No. The solders are OK if they look app. and if the receiver operates well bigger resistance should be tried out. and the pin lies down on its place with the aid of the bodkin.4.15. comprised by the aforementioned components. If it needs to be corrected. with iron head simultaneously touching both the tin and the pin end. All the components apart from TDA7088T are mounted on the opposite side of the board. half a second. the tinol wire is removed first. the iron tip is simultaneously put on the top of the leg and the copper below it. and gets soldered. their pins are put through the holes and soldered through the holes.17c. as on Pic. and the pin No. say.16a shows 3x enlarged picture of the IC and the surrounding lines.4.9 is soldered.17b. Pic.1 and 9. * Pic. The listener can now hear the left half of the performers from the loudspeaker placed on its left. All radio transmitters operating in this range are stereophonic. 4. Making an introduction to this part.2. The panelmount switches can also be used. therefore two signals are exiting it. the information that was used to perform the frequency modulation in the transmitter. * Any audio amplifier described so far can be used. The readers that wish to get acquainted in more details with the stereophonic broadcast basics can refer to the “Radio Receivers” textbook. They are being amplified over two identical audio amplifiers. a 20 cm piece of wire can also be utilized. exiting the FM detector the LF signal is obtained. However. but the one. a operating principle of the stereophonic radio receiver shall be considered. * Instead of the antenna. between the left and right .8.2. in which case they are connected to the board by wires (pic. i. then reproduced over two same loudspeakers. It means that. Exiting the coder we have the multiplexed signal Mpx which contains. Besides the fullscale LF signal used by the monophonic receiver. one may notice that they are identical.e. The board is mounted fairly close to the box edge. up to the block called "The Decoder". called the "composed" (KS) or "multiplexed" (Mpx) signal.15e). Mpx signal is obtained on the output of the FM Detector and is then led to the decoder. making an impression to the listener as if there’s a third loudspeaker. but their signal is designed so that monophonic receivers can also read it. and the right half from the loudspeaker that is placed on its right. located in the middle. this is not an ordinary LF signal. as on pic.g. if a direct broadcast of some band music is performed. in an indirect manner. the left part of performers is being recorded with one microphone (the signal marked as L). whilst the right side is recorded with the other one (it’s a R signal). both left (L) and right (R) signal.4.g. In that case small modifications on the PCB lines would probably be necessary. The performers that are situated in the middle of the orchestra are being equally reproduced from both loudspeakers. from 88 MHz till 108 MHz.pushbutton switches can also be used. its block diagram shown on pic. so that the switch shafts are passing through the panel. In the receiver. Comparing this diagram with the one of the monophonic receiver given on pic.6. and that the buttons can be mounted on the outside.4. Stereophonic Receiver Built with TDA7088T Stereophonic radio broadcast is performed in the ultra short waveband.4.4. for the IV grade of the Electrotechnical Highschool. the one with LM386. Frequency modulation of the transmitter is being performed with the Mpx signal. e. it also contains the socalled auxiliary signal which allows the separation of left (L) and right (R) channels in the stereophonic receiver. as already described. This stage plays a role complementary to the one of the coder in the transmitter. E. the L and D signal.18. These two signals are being led in the FM transmitter in the stage called “the coder”. performing the compatibility.2. * L3. the latter was discussed in PE5.2 mm CuL wire.one. preventing them to “go to ground” over the 47 mF capacitor or over the TDA7050T output. Electronic circuit of a portable stereophonic radio receiver with headphones reproduction. the outside antenna is connected. made with TDA7088T is shown on pic. the listener has a picture about the layout of the performers in space. If telescopic antenna is to be used.4.14. to the point where. to pic. these coils should be omitted. Based on all this. which significantly improves the total musical impression.19. This is accomplished by connecting one of the headphones’ contacts from the plugin.4. The coils represent big resistance to the station signals. It is a receiver whose practical realization was described in the previous project. . with decoder with TDA7040T and dual audio amplifier with TDA7050T blocks added.4. acc. over the 10 pF capacitor. Each coil has 3 quirks of the 0. L4 and L5 are HF chokes that allow for the headphones cable to be used as a reception antenna. threaded through ferrite pearls. as shown on detail in the right corner of the pic.19. . . . . . . . . . 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