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A High-Quality DAB+/FM Tuner, Pt.2

Last month, we introduced our new DAB+/FM Stereo Tuner and gave the circuit details. This month, we show you how to assemble the two PC boards and install them into a low-profile steel case.

By Mauro Grassi

If you want to build this project, there’s just one way to go – buy the complete kit from Jaycar Electronics (see panel).

There are several reasons for this. First, the Venice 7 radio module is not readily available from other sources. Second, the main PC board supplied with the kit will have the surface-mount dsPIC microcontroller (IC1) already soldered in place (and pre-programmed). And third, the Jaycar kit will come with a pre-punched custom steel case with screened lettering to give the unit a professional finish.

Having the microcontroller already soldered in place is a real bonus. It will save you the hassle of having to solder this part in by hand and risk ruining the main board.

The DAB+/FM Stereo Tuner will take you quite a few hours to build, so it’s best to tackle it in stages. There are two PC boards to build: (1) a main board which carries the Venice 7 module, the microcontroller, the power supply components and several input/output connectors; and (2) a front panel board which carries the LCD, switches, rotary encoder and the IR receiver.

You will need only a few basic tools to build the tuner – a soldering iron (preferably a temperature-controlled type) with a fine tip, a pair of needle-nose pliers, a pair of side cutters and an Allen key. A DMM (digital multimeter) is also necessary.

Main board assembly

Click for larger image
Fig.3: install the parts on the main PC board as shown here. Make sure that all polarised parts are correctly oriented and note that CON4 is installed on the rear of the board with its keyway towards IC1.

We’ll begin with the main board assembly. This double-sided board is coded 01110101 and measures 114.5 x 194mm. As mentioned, it’s supplied with IC1 already soldered into place and should be carefully inspected for defects before proceeding.

Refer now to Fig.3 for the main board parts layout. Begin the assembly by installing the resistors, taking care to fit the correct value at each location. Table 2 shows the resistor colour codes but we strongly advise that you check each one using a DMM before installing it.

Follow these with the three 1N4004 diodes (D1-D3). These must go in with their striped ends orientated as shown. The four IC sockets (for IC2-IC5) can then go in with their notched ends matching the board layout.

Follow these with the ceramic, monolithic, MKT and electrolytic cap-
acitors, in that order. Make sure the electrolytic capacitors go in the correct way around and note that some of the 100nF capacitors are MKT types (around the regulators and op amps) while the others are monolithic types (around IC1 and IC2).

Note also that some 100nF monolithic capacitors have a lead spacing of 0.1-inch (2.54mm) whereas others have a 0.2-inch (5.08mm) spacing. The PC board uses 0.1-inch spacing so if the capacitors supplied are 0.2-inch types, you will have to bend their leads with needle nose pliers to make them fit.

Next, install the 2-way screw terminal block for CON1. CON 2 & CON11 are 3-way screw terminal blocks but it’s not necessary to install these (or any other parts marked with a red asterisk) and they are not included in the kit. If fitted, they give on-board access to the two stereo audio outputs, which may be useful for a future modification.

The BC337 NPN transistor (Q1) can be installed next, followed by the three BC327 PNP transistors (Q2-Q4). These transistors must go in the right way around. Push them down onto the board as far as they will comfortably go (but don’t over-stress the leads) before soldering them into place.

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