On a whim, I bought a Maplin project to build. I needed an audio signal generator for something I’m planning and the £15.99 Function Generator Kit seemed to fit the bill. I have a very local Maplin shop where the staff know me by name and I was passing by today so I picked one up. This particular board attracted me because it utilises an ATTINY2313 chip as a generator along with a resistor lattice.
It took around 45mins of careful construction after which I had a very functional Audio Signal Generator.
I did wonder though; Had the ATTINY’s lock fuses been set? AVRs have special fuses in them which allow the programmer to ‘Lock’ the chip after programming, preventing anyone from reading the code. The Function Generator PCB didn’t have any provision for ICSP (In Circuit Serial Programming) so I had a look around the workshop to see if I could make a testing jig. Something that would be useful in the future. I settled on a small, inexpensive prototyping PCB I had bought. I mounted sockets for 28-pin and 8-pin chip variants and a set of headers along each side to access the chips pins. I then soldered sets of three connector headers above and below to act as power rails. I also bridged the power rails into the prototype boards inner rails so the power would be available at both ends of the board.
Once I had checked all the solder joints, I mounted the ATTINY from the Signal Generator on the test board and connected the relevant pins up by checking the datasheet. I had already made a back-to-back ICSP adaptor to use flying leads with my AVR ISP MkII. This allows connection via flying leads rather than the 6-pin ICSP connector provided by the programmer.
I connected the flying leads to the AVR ISP MkII via the back-to-back adaptor and fired up the jigs power. I plugged the AVR ISP MkII into the USB port of my PC and I was pleased to see a green light indicating that all was well.
I then loaded AVR studio and connected to the programmer. I was astounded to find that the lock fuses had not been set and that I could freely do a dump of the Flash area! I checked the EEPROM area too but there is no data there. I have kept a ‘backup’ of the flash to study and in case I need to program a replacement chip.