Universal Adapter for Arduino/ATmel USBasp programmer

A while back I fabricated a socket adapter for my USBasp programmer for use with the eight pin ATtiny85 DIP package microcontrollers. I used a RadioShack Catalog #: 276-150 prototype board, an 8-pin socket, some header pins and wires to create it. Simple, easy and it does the job.  By the way, the Betemcu.cn USBasp programmer is readily available on eBay for under $9, including postage. It uses Thomas Fischl’s design and works flawlessly.

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However, when my activity included ATtiny84 and ATtiny2313 chips I was faced with the prospect of building new boards for each microcontroller type.  Instead, I opted for building a universal adapter that would work for all of the ATmel microcontrollers.

I accumulated parts through eBay so as to minimize costs. Most important was the 40-pin ZIF Socket for big or slim chips. It cost $2.95, including delivery. I purchased it from eBay vendor grand_sky. My single row male 1X40 header strips cost 20 cents each ($1.95 for 10) from eBay Hong-Kong seller wulor, but many people sell these. My 1×40 Pin 2.54 mm Single Row Female Pin Headers were 32 cents each. My single-sided PCB board material was ordered from eBay seller abcfab for 52 cents per 4X6-inch board.

To design the universal adapter I used gEDA‘s schem and PCB packages.

A Printed Circuit Board layout consists of applying upon a copper laminated board, an acid-resistant pattern that represents the areas that are to retain copper after etching in an acid solution (etchant). Areas of the copper laminated board that are exposed to the etchant will be dissolved away, leaving the areas under the acid-resistant pattern intact. The positive layout below is printed in reverse onto a special paper that will easily release the toner when heated. Laser printer toner is a finely ground polymer plastic that is fused to the paper by heat. The trick of the “toner method” is to get the toner to transfer from the paper to the copper laminated board once it is re-heated. There are several paper solutions for the “toner method”, some better than others.

Regardless of the type of paper used, the process is to place the reverse image positive laser print with the toner touching the metal surface of a clean copper laminated board and then apply heat and pressure to loosen the toner from the paper, permitting it to transfer to and adhere to the copper laminated board. I used use a common clothes iron as the heat source, although a laminating machine designed for identification cards is successfully used with one commercial product. The laminating machine will not work with Brother brand laser printers because the toner’s melting point is too high for the laminating machine. With Brother brand laser printers you must use a clothes iron – although, I am considering a carpet seaming iron sold by Northern Tools and Amazon because it has a rectangular shape and higher controllable temperature.

Once heated under pressure, the toner ends up adhering to both the paper and the copper laminated board. The paper/copper laminated board is then soaked under water and the waterlogged paper floats away if you use dextrin coated paper, such as that made by PulsarProFx.

I also use PulsarProFx’s Green Toner Foil because the toner adhering to the copper laminated board is porous and, even though you cannot see it with the naked eye, there are sufficient holes for the etchant to penetrate the toner traces and remove metal that you do not want removed. The Green Toner Foil is ironed onto the copper laminated board resident toner, creating a smooth, impervious surface on the top of the toner traces, resulting in superior board etches.

You can obtain a correct size copy of the etch pattern above HERE.

My finished board is shown below.

NOTE: Learn from my mistake and mount the ZIF socket with the handle facing away from the socket.

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