Introduction

This project is an instance of the UsbProg project created by Benedikt Sauter. Bene released the schematics, board layout and firmware as an open-source project. I took that project and made these modifications:

• Changed CONN1 to a type Mini-B receptacle (so it would be surface mount).
• Changed most parts to have surface mount packages (except jumpers and headers).
• Added capacitors C1 and C2 for decoupling.
• Added CONN3 2x5 pin header for Port A (the ADC inputs).
• Added JP3 jumper header to choose which pin controls LED1.

The addition of JP3 has special considerations. Place a jumper across JP3 pins 1 and 2 to make UsbProg-SHARP exactly compatible with the original UsbProg.

Or, optionally, place a jumper across JP3 pins 2 and 3 so that LED1 is controlled by PD7. This frees up PA4 so that all 8 pins of PORTA can be used. PORTA is available via CONN3. When the jumper is in this position, the UsbProg-SHARP board is no longer compatible with stock UsbProg firmware and requires a special version of the firmware that has yet to be created.

Myself and other members of SHARP are making circuit boards for this project using at-home etching techniques.

Status

The board works when connected to a Win32 PC and with an update to the firmware, enumerates on a Macintosh as well! However, there is still no Mac OS X driver; work shall begin on that soon.

Log:

• 2007/11/12: I corrected the values for C8,9 to 27 pF in the BOM after receiving a review from Steve. C8,9 still have the wrong value in the schematic.
• 2007/08/12: Benedikt emailed me a new firmware binary for avrispmk2klon this morning that allows the UsbProg-SHARP to enumerate on a Mac! By the end of the day, Bene had put the new code in the subversion SCM.
• 2007/07/30: Fuse settings were changed to be in agreement with those suggested here.
• 2007/07/29: The board communication problems were due to 3 ATmega32 pins not making contact with their pads. Reflowing those pins solved the issue. The board is functional. Fuses were set so the ATmega32 will use the clock from the USBN9604.
• 2007/07/28: Etched and populated the board rev 2007/07/26. Attempted to flash the ATmega32 via ISP, but niether AvrDude nor AVR Studio could communicate with the board. An effort is underway to debug the communication problem.
• 2007/07/26: Changed the 2x5 headers footprints to be thicker (larger annulus).
• 2007/07/22: Changed the footprint of the two 2x5 Headers to be through-hole. Arty felt that the surface mount headers might peel-off when subjected to the forces on a ribbon cable.
• 2007/07/19: Updated schematics and layout to UsbProg 3.0 (per schematic on UsbProg mailing list)

Schematic

The following schematic represents UsbProg-SHARP which includes the changes listed above and some small "clean up" changes per my own preferences.

Here is the EAGLE schematic file: usbprog.sch

Layout

I created the board layout from scratch. I did this because my goal is to make a layout that can be etched using home-brew techniques. This means I have put as many traces on the top side as possible. All traces are 10 mil (0.010 inches) and in-between spacing is 10 mil or greater. There are roughly seven bottom-side traces that will require air-wire soldering. Most bottom-side traces end at a via or pad. The holes for the vias do not need to be drilled, but drilling does make placing the air wires easyer. Alternatively, a fine wire (for example, wirewrap wire) can be soldered to the via's top pad.

I also changed a few parts, such as the USB connector to type mini-B, so that the part would be surface mount on the top side. One exception to this is that both connector headers are through-hole. This was done because the pads for a surface mount header might not be able to withstand the physical forces on a ribbon cable.

Here is the EAGLE board layout file: usbprog.brd Here is a mirrored PDF so you can print a transparency and etch your own. A mirrored layout is given so that you can place the toner side of the transparency face to face with the etch-resist side of the copper board.

Parts List

The following table presents the parts list for a single UsbProg-SHARP board:

Results

The first attempt at etching a board was on 2007/07/22. This attempt was not successful because the layout transparency was scaled 5% smaller than the necessary size. However, the etching technique worked very well and the resulting board looks clean despite the many fine-pitch traces and footprints. We also learned a few things about solder paste and how to use a hot-plate to simultaneously solder many components.

The second attempt at etching took place on 2007/07/28. With the transparency at the correct scale, we etched the board (revision 2007/07/26). Again, the etching process produced a fantastic board. Clean traces with empty spaces in between. We populated the board using Kester solder paste and a hot air gun set to 302 degrees C. The order of the components was as follows: USB mini-B connector, all 0805 components, crystal, USBN9604 and the ATmega32. The header connectors, jumpers and seven air wires were then soldered using a solder pencil.

After one night of debugging, the board is able to communicate with an Atmel STK500 and be programmed! The board is functional. A second day of work and the board is recognized by a Win32 PC and operates as a clone of AVRISP mkII.

Jumpers

This section explains the purposes of the four jumpers on the UsbProg-SHARP and the meanings of the different settings.

• JP1: Connects either Vcc or GND to the ATmega32's RESET' pin. Connect JP1 pin 1 and 2 to apply Vcc to the RESET' pin. This is the default setting and is used for normal operation of the UsbProg. Connect JP1 pin 2 and 3 to apply GND to the RESET' pin. This setting keeps the ATmega32 in reset state which is needed to re-flash the ATmega32 (a.k.a. Bootloader mode).
• JP2: This is an output connector for the ATmega32's USART. You should not apply a jumper to any of these pins. JP2 pin 1 is GND, pin 2 is RX and pin 3 is TX. The pins are at "TTL" level and cannot connect directly to a PC's serial port. An RS-232 level shifter is necessary to connect to a PC's serial port.
• JP3: Selects which ATmega32 pin lights up LED1. Connect JP3 pin 1 and 2 in order for PA4 to light LED1. This is the default setting (compatible to the original UsbProg). Connect JP3 pin 2 and 3 in order for PD7 to light LED1. This setting should only be used if you need all PORTA pins on CONN3 when running custom firmware on the ATmega32.
• JP4: Serves to connect Vcc (which is +5V from the USB bus) to CONN2 pin 2. The default setting is to place a jumper on JP4 so that +5V is applied to the target device. An alternate method is to remove JP4 so +5V is not applied to target devices that supply their own power.

Engineering Notes

Cload = Cxtal^2 / 2*Cxtal + Cparasitic

20 = Cxtal^2 / 2*Cxtal
Cxtal = 40 pF

20 = Cxtal^2 / 2*Cxtal + 4
Cxtal = 32 pF

cd ~/Code/other/usbprog/avrisp...

avrdude -p atmega32 -P /dev/cu.USA19H191P1.1 -c stk500v2 -U flash:w:main.hex

avrdude -p atmega32 -P /dev/cu.USA19H191P1.1 -c stk500v2 -t
avrdude> dump lfuse
>>> dump lfuse
0000  e1                                                |.               |
avrdude> dump hfuse
>>> dump hfuse
0000  99                                                |.               |

avrdude> write hfuse 0 0x89
>>> write hfuse 0 0x89
avrdude> write lfuse 0 0xe0
>>> write lfuse 0 0xe0

avrdude> dump hfuse
>>> dump hfuse
0000  89                                                |.               |
avrdude> dump lfuse
>>> dump lfuse
0000  e0                                                |.               |
>>> quit