USBTinyISP using ATTiny85

Some time ago I’ve found a project of an USB programmer that used an ATTiny85 microcontroller to emulate all the functions of a FTDI programmer. The reason I wanted to build this programmer was mainly the cost and availability of the parts. I had some ATTinys laying around, but the problem were those two 3.6V Zener diodes that are not commonly available everywhere so I’ve managed to buy some sort of Zener diodes kit from banggood, and it was nice to found that certain value in the kit. However, Zener diodes are kind of optional and if you search about this subject you can easily find people reporting that the widely used 1N148 diodes connected in series are useful to drop the voltage to certain levels if Zener diodes are unavailable.
Anyways, the inspiration came from this site. I’ve used the drawn schematic to make my own in Cadsoft Eagle.

This is the original schematic…

And this is the schematic made by myself…

Schematic USBtinyISP

With its corresponding PCB design.

PCB USBtinyISP

As you can see in the schematic, the values of resistors connected on Attiny’s pin 2 and pin 3 are between 68 and 100ohms. Also the value of the pull-up resistor connected between VCC and D- trace is between 1 and 2Kohms. In the original project values like 68ohms and 1.7Kohms are used, but because I don’t have those kind of resistors I had to improvise and use 100ohms and 1K resistors. The ceramic capacitor has the right value, because I’ve got hundreds of them laying around. 🙂
Well, after printing the layout on Oracal 741 glossy paper and preparing the PCB, the result was this one…2015-03-23 13.01.31

The next picture is after corrosion bath in Iron chloride (FeCl3)…

2015-03-23 13.55.03

After drilling the holes for components and mounting some of them…

2015-03-23 14.56.19

Aaand the finished product.

2015-03-23 15.16.33

I’m not going to bother you with programming the ATtiny85, because you can find a bunch of tutorials on internet of how to do that. The .hex file can be downloaded from HERE, and it can be uploaded into the ATTiny85 using Arduino as ISP with Xloader Arduino hex uploader.

I will make a video to show you how this programmer works, but meanwhile you can check the schematics and the PCB design if you want to make your own device! Cheers!

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