TEP FM RADIOCode: PACK 1403

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LIT0091

For more information please contact:

Mindsets (UK) Limited

Unit 10The IO CentreLea RoadWaltham CrossHertsEN9 1AS

Tel: 01992 716052Fax: 01992 719474Web: www.mindsetsonline.co.uk

Copyright © 2009 Mindsets (UK) Limited

TEP FM Radio

VERSION 1

TEP FM Radio

VERSION 1 2

TEP FM RADIO

INTRODUCTION

The TEP radio is a high performance FM receiver based on theindustry-standard TDA 7000 chip. The radio is supplied as acompletely populated printed circuit board (PCB) that requiresonly the addition of five external components: battery,loudspeaker, tuning control, volume control and small aerialsupplied within the pack. A working radio can be assembled fromthe parts provided in the TEP radio pack, but other externalcomponents can be substituted to provide a choice of controlfunctions - and improved sound quality.

Designing and making a complete radio offers a huge range offascinating and potentially challenging design decisions and is avery practical vehicle for teaching many of the principlesinvolved in radio electronics and acoustics.

This handbook provides basic instructions for the completion ofa working radio and also discusses key component and designoptions. It also includes useful information and technical data inthe study files section. Like other TEP 'special' publications, thisbook can be used in the classroom in a variety of ways. Forexample, the first part may be photocopied as a basicconstruction handbook; selected parts can also be provided asback-up information or to assist pupils in making designdecisions; or the whole book can be made generally available as areference resource.

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OPTIONAL RADIO COMPONENTS

The following optional radio components are available fromTeaching Resources.

• Loudspeaker approx 125mm Ø• Stereo headphone socket• Small telescopic aerial• 10k Linear slider variable resistor (for tuning)• 10k Linear slider variable resistor (logarithmic for volume

control)• 10k variable resistor for volume control with integral on/off

switch• 10k multiturn variable resistor (for tuning)• 10k multiturn pre-set resistor (for tuning)• 2 pole multiway switch• Loudspeaker covering fabric (grey)• Loudspeaker covering fabric (black)• Matrix board (for loudspeaker grill modelling)• Stereo headphones

Linear slider resistor

Multi-turn variable resistor

Stereo headphone socket

Loudspeaker (outlineshape indicative only)

Headphones

Multi-turn pre-set resistor

Small telescopic aerial

TEP FM Radio

VERSION 1

TEP FM Radio

VERSION 1 3

ASSEMBLING THE RADIO A basic working TEP radio can be assembled using only thecomponents supplied in the TEP radio pack. However, a widevariety of interesting variants and design options are discussed atlength in the various sections of this handbook.

COMPONENTS:

Printed circuit board (PCB)

10k variable (linear)resistor for tuning *(marked 'B' on casing)

Loudspeaker *NOTE: The TEP radio is tuned byusing a variable resistor and a varicap(whose capacitance depends onvoltage). This arrangement is cheaperand more flexible than using avariable capacitor.

Radios are a rich resource fordesigning and making andmost pupils and students willwant to look at wider designand styling options - including'retro-styling'.

1.5 metres assortedcolour stranded wire

10k variable (logarithmic)resistor for volume control(marked 'A' or '-2' on casing)

2 Battery snaps(1 snap as illustrated for PP3battery plus larger snaps for

PP7 and PP9)

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Step 6TEST and TUNE the radio by turning the volume control to thehalf way position. A background 'hiss' should be heard. Turn thetuning control slowly backwards and forwards through its fullrange and at the same time adjust the inductor using the specialtool provided. When the inductor is correctly set, it should bepossible to receive the main advertised FM stations within thefrequency range 90MHz to 106MHz. It may be useful at the sametime to have a commercial radio tuned in to act as a reference forcalibration of a tuning scale etc.

Radio frequencies:

Radio 1. 97.6 - 99.8 MHzRadio 2. 88 - 90.2 MHzRadio 3. 90.2 - 92.4 MHzRadio 4. 92.4 - 94.6 MHzVirgin. 105.8 MHzClassic FM. 100 - 102 MHz

It is important to note that the loudspeaker needs a baffle. This isnormally provided by putting the loudspeaker into an enclosure.The difference in sound quality and volume that this makes canbe demonstrated by listening to the sound before and after handsare cupped around the loudspeaker.

If stereo headphones are used, they should be connected inseries. This is achieved by wiring the socket supplied fromteaching resources as shown. At maximum volume, the outputpower of the radio will be excessive for most headphones. Tolimit the maximum volume, resistor R4 on the PCB should bereplaced by a higher value - e.g. 220 ohm.

If the radio fails to work first time:

• check that batteries have been correctly inserted in the batterybox if used. Check on battery condition

• disconnect the battery andcheck all external leads forcontinuity - including thebattery snap. This can bedone using a continuitychecker or multimeter. Foreach check, place oneprobe on the PCB trackimmediately adjacent tothe soldered joint and theother at the extremity ofthe component tag towhich a lead is soldered.This will show up possiblefaults in soldered joints.

NOTE: Almost all reportedproblems arising from self-assembly kits are due tofaulty soldering - either'dry' joints or bridgingacross PCB tracks byexcess solder.

Rear of socket

To board

TEP FM Radio

VERSION 1

TEP FM Radio

VERSION 1 4

Step 1Solder on the battery snap leads - ensuring that the red lead isconnected to +ve on the PCB.

Step 2Solder on the loudspeaker using two lengths of stranded wire.The loudspeaker can be connected either way round.

Step 3Solder on a length of approximately 0.5m stranded wire to act asan aerial.

Step 4Solder on the tuning and volume control variable resistors asshown using three lengths of stranded wire for each. Thevariable resistor marked 'A' is for volume control and the onemarked 'B' is for tuning.

For each variable resistor, the two outer leads can be connectedeither way round, but this will determine the direction of tuningand volume control when the resistor spindles are turned. It isessential that the centre lead goes to the centre connection ofeach variable resistor.

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Step 5CHECK that all connections are correct and secure and thenconnect a 9 volt battery. A PP3 type will do for test purposes at lowvolumes or with headphones. Only the following are recommendedfor permanent use:

• Six AA size batteries in an appropriate holder• PP7 type 9v battery• PP9 type 9v battery

Even at moderate volume levels, the voltage of a smaller 9vbattery may drop below the required 7 volt threshold and theradio output will suddenly lock into a continuous howlingsound. This can be rectified by turning down the volume or, forexample, replacing a 'flat' battery.

PP3

PP7

PP9 6 x AA

Relative battery sizes