TT’s Jottings-Blog of VU2SWX

This post is for my students at college of engineering Attingal . We are going to get vacation during May and June. I think your semester examination will be over by April end. I have a small project which some of you can take up during this summer vacation. The project is related to amateur radio. If you are able to do it, this will be a fine minor project for your sixth semester. However, my aim is to introduce some of you to micro controllers and embedded systems early in your course. I don’t find many home brewers among students nowadays. This will be an ideal opportunity to learn a few tricks.

Now here is the idea. I have a few fixed frequency VHF transceivers. They are Philips Portaphone SXA rigs made around 1977. The figure below show one.

The transceiver can take 6 fixed frequency crystals on the receiver as well as transmitter side. That means it has only six fixed channels. Now ,I have a pair of crystals cut for the Trivandrum amateur repeater. (RX 145.600Mhz TX 145.00Mhz ). That means I am operating it only on a single channel.

I want to convert it to a variable frequency transceiver by adding a DDS ( direct digital synthesis ) controlled oscillator, replacing the crystal oscillator.

Your Task will be to build a micro controller board and a DDS board and drive the tranciever for covering the amateur band of 144-146 MHZ. You can choose either a PIC or an Atmel processor. For the DDS , an Analog devices AD9851 will be sufficient. There are some similar projects on the net. You can look here.

Do a search on google for DDS VFO .You will find more links. This project will be on similar lines. But the programming and driver circuit for the transceiver will be different . The output of DDS should be switched between receiver and transmitter frequencies. I will give you more details later.

You are expected to do the following

a) Study of the chosen micro controller.

b) Design the board and simulate it .

c) Study about DDS.

d) Design a DDS board.

e) Design PCBs for both the boards and build

f) Test the prototype in lab.

g) Make a suitable cabinet and build the final product.

A detailed requirement specification will be given later.

I have the following stuff with me .

a) Some PIC micro controllers

b) DDS chip AD9851

c) Some LCD displays

d) Assorted components.

I can provide you with a PIC programmer if you choose PIC. I can fund you for any costly ( say greater than $2). Rest of the stuff ,you will have to find out.

I can take 3 guys . Each one should do it independently.

You must be willing to work during vacation. I will be coming to college on a few days to college during vacation. Otherwise, you can interact with me on internet . A PC and an internet connection at home is a must. All designs and programs should be posted on internet and must be under a suitable free license.

I will give some preference to second year guys. (but first years can also be considered.). If you are interested , drop me a mail at vu2swx at gmail. com.

I have been trying to develop a general purpose prototyping board for the Microchip PIC 16F877A . My aim is to build a board with the following features

a) All ports and other on board devices must be easily taken out to a solderless bread board.

b) In circuit serial programming.

c) boot loader.

d) the board will have some switches , an LCD module , a few LEDs and a pot for analog input simulation.

My design is almost complete. In fact, there is nothing new in the design. I have done cut and paste from several circuits.

I am planning to post schematics and experiences while building the board on this blog.

Today, I have completed the in circuit serial programming module(ICSP). This is based on this article by Ian Lesnet.My final prototype is shown below. The pcb layout for home brewing via toner transfer method is here.

The original article uses a PCB mounted 9 pin D connector. I I found it inconvenient ,after soldering the board. Instead , Ifixed a piece of ribbon cable. My programming set up is shown below. Just wire the connectors to the appropriate pins.

The board lacks any indicators. I am planning to redesign the pcb with 2 indicator LEDs later.

The software I used is winpic800 . It works like a charm. ( The default interface is in Spanish, change it to english by selecting Idioma->English in the main menu)