In the previous article, I described the features I want in this transceiver, and sketched out some ideas of how its user interface might accomodate these features. In this article, I start the construction.

[See the full list of articles in this series HERE]

The transceiver is powered from a single 12 (13.8)v source, such as a sealed lead-acid battery, bank of rechargeable cells or power supply. Protection is provided to prevent swapping the input leads, then the power is smoothed and converted into additional 9v and 5v supplies. Several connectors are provided for the various modules that comprise the complete system.

The original Easibuild’s power supply was a little simpler, with 12v being protected by fuse and ‘idiot diode’, and a little smoothing. 5v regulation was only needed by the VFO/buffer, and so was done in that unit. The receiver also converts the 12v into 8v for the NE612 mixer – I’ve retained this scheme.

In this revised power supply, I’ve added 7809 and 7805 regulation with smoothing electrolytics, and changed the idiot diode to a transient voltage suppressor. The use of transient suppression diodes, and idiot diodes generally was covered in an article in Practical Wireless, June 2015, by the Rev. George Dobbs G3RJV. Joe N2CX also has a useful article at his blog in which he recommends using a transient suppressor diode. For more on why series idiot diodes are a bad idea, see this article.

Input to the transceiver is via a Kobiconn 163-4304 power jack, available from Mouser, but Maplin’s JK09K, or Proto-pic’s PPADA610 are suitable. The matching plug for this is a Mouser 1710-2131, or Maplin HH60Q. The positive power then passes through a 1A fuse, in a 5x20mm Schurter fuse holder, and then to the switch on the volume potentiometer. From there it – and the negative from the input socket – are connected to the 12v connection on the power board.

The output power connections are 4-pin 2.54mm pin headers, which I’m using throughout the project for various interconnections.

Schematic

The schematic for the supply is shown below (click diagram for a larger version):

Construction

I’m using prototype board for many of the modules in this project, for no other reason that it’s really cheap. I bought 20pcs of the board below from an Amazon seller in China, called Hielec, for £3.30.

This prototype board is a little thinner than the Veroboard I’m used to, and the solder pads are not perfectly aligned with the holes, but it’s good enough. There are 18×24 holes per board.

The board layout I used is shown below (click diagram for a larger version):

This is the view from the component side; I mirrored the above bitmap horizontally in GIMP and printed it to ensure I got the wiring on the underside right.

It could be smaller: the layout leaves some space around the voltage regulators, so that any heat they generate is away from the nearby smoothing capacitors. Don’t want them drying out! The transient voltage suppressor is quite large, so needs the space allocated. The capacitors are around 6mm diameter. All wiring on the bottom of the board used 1/0.6mm wire, stripped as necessary. Although the circuit only takes up a few columns of a prototype board, I haven’t cut it down yet: I might need some extra board space for patching/fixups later.

Parts list

All parts were obtained from Amazon sellers, Mouser electronics, RS components, Hobbytronics, CPC, or Maplin. Some I had anyway. For detail on cost as of mid-2015, vendor website URLs of each component and where I obtained it, see the Excel parts list spreadsheet [Excel 2011 For Mac .xlsx format].

Part Value
12V_IN 2-pin male 2.54mm header
12V_IN_PLUG 2-pin female 2.54mm plug
D1 1.5KE18A transient voltage suppressor
C1, C2, C3 10μF 50V electrolytic
IC1 LM7805
IC2 LM7809
PWR1-6 4-pin male 2.54mm header
… not shown on this schematic; part of the case/front panel …
VR1 100kΩ log pot & switch
J1 Power socket; Kobiconn 163-4304
F1 1A 5x20mm fuse
FH1 5x20mm Schurter fuse holder

Testing

I assembled the board, checked for shorts with a magnifying glass, checked continuity of the main traces to the output pin header cluster, then wired it into my prototype breadboard, connecting the power jack, fuse, and on/off switch. Applying power from a pack of 10 1.2v Ni-Mh rechargeable AA cells, I measured voltages in the correct ranges on all of the pin headers.

Conclusion

This board is general-purpose, and I expect to reuse it for future Arduino Micro-based amateur projects.
In the next article, I’ll describe the Arduino digital control board….

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