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)
Electronics, Micro controllers
I have seen several tutorials on the Internet for making professional looking PCBs at home. In fact, I attempted making a few last year with limited success. However, I managed to perfect the technique yesterday. The procedure I used is described in this tutorial.
I made some minor changes to materials and made a few perfect PCBs. First of all, the quality of bare copper clad sheet is very important. There are two type of copper clad sheets available here (in Trivandrum):- Paper phenolic and Glass epoxy. Never use paper phenolic type for this technique. The copper layer detaches itself from the paper phenolic substrate when you apply heat.
Secondly, clean the surface of the glass epoxy board using Brasso. Brasso is available in hardware/stationary shops. Put 5ml Brasso on the copper clad sheet and rub it with cotton waste. The oxide coating on the board will be completely removed and its surface will become shiny. The paper I used is called “art paper” , as per the local store keepers nomenclature. A2 size sheet cost around Rs.5.
I printed the mirrored layout on a HP1020 printer at 600dpi. The iron was set at the maximum temperature range and heated for some 5 minutes. Then I fitted the printout on the copper clad and applied the iron for another 3 minutes ( until the paper turned slightly brownish) . The board was them socked in water and I could peel of the paper. The pattern was perfectly transferred to the board.
I have observed the following while developing the procedure.
a) Cleanliness of the board is very very important. Give extra care to it if you ever attempt making PCB at home.
b) Transfer the image as soon as possible after printing.
c) Keep the temperature of the iron maximum.
d) ( In Trivandrum, you should attempt it only after 2. AM in the morning. Your power supply voltage will be 230v around that time. Normally, I get 160 -190v during day time. So this condition applies to Trivandrum only )
I will describe my experiences in receiving long distance FM here.
For receiving long distance FM (or FM Dxing) the first thing you need is a good radio. Good receivers are hard to find nowadays. If you can find a Phillips of Sony radio you are half way through. (I think Phillips no longer markets radios in India). There are several cheap Chinese radios available in the market. They are ok for a casual Dxer. Some radios today can automatically scan the FM band for stations. I don’t recommend them.
Next step is to build an antenna. There are several possibilities for this . Some of them are dipole. folded dipole or even a quad.
First let us see how to construct a simple dipole. The FM band is from88MHz to 108Mhz. We will design a dipole tuned at the centre of the FM band.( ie 98Mhz)
The formula for calucualting dipole length is =468/Frequency in Mhz.
I n our case the length works out to be 4.78 feet.
Get hold of 2 pieces of copper wire.( If you cannot find, buy two pieces of 1/2inch aluminum rod or welding rod. As a ham I use welding rods for all my VHF antennas) . Fix them on a PVC pipe ( Use your ingenuity for fixing them. ) the Dipole antenna has an impedance of approximately 75 ohms. You can buy sufficient length of coaxial cable for connecting your dipole to the radio.
Fix the dipole at a good height. Keep it horizontal ( FM uses horizontal polarization ). The other end of the coaxial cable must be connected to the radio. Most of the modern radios use a telescopic areal. Fold it to the minimum position and fix the inner wire of the coaxial cable to th telescopic areal .The outer braid may be connected to the negative terminal of the battery.
Some of the older TVs used to have rabbit ear antenna. ( a small detachable dipole whit adjustable length) If you can locate one , it can be directly used as a dipole.
Your mileage may vary depending on your location,atmospheric conditions etc
I have seen folded dipoles and rectangular loops suitable for FM reception in some of the electronics shops in Trivandrum. They are mainly used here to receive Suriyan FM broadcasting from Tirunelveli. I don’t know whether they are still available.
My ham radio licence has definitely rekindled my interest in electronics. While searching for some information I have come across the following forums.
All of then are invaluable resource to home brewers. Electronics lab forum has some excellent howtos and construction ideas. They also have a resources forum where you can find some of the best books, provided you dont mind reading some pirated books .
The following link has some common data sheets. I have made a local copy of this archive for easy reference.