encounters with electron•ics / by flabbergast

HVSP fuse resetter

Having looked at simpleavr’s HVSP fuse resetter, I wanted to make one myself, since I play with attiny85’s and sometimes I want to reset the fuses to “unlock” an attiny with disabled reset.

First, I built one just like simpleavr’s, on a mini breadboard:

But then I wanted to make it “permanent”, so I moved it onto Sparkfun’s cute Solderable mini protoboard:

I wanted to make the 4 digit seven segment display removable, as well as have access to the attiny2313, so these two are mounted on headers and a socket, respectively.


While the breadboard version is powered through jumper wires, to make the usage of the soldered version more convenient, I soldered a standard barrel receptacle to it: now I can just use any 12V power supply - I have a couple of those, since the DSL and other routers usually come with one.

The biggest change from the simpleavr’s schematic and implementation is that I’ve added a capacitor (100uF) to stabilise the regulated power supply: without it the device didn’t work pretty much at all (I’ve seen only some jitter on the display). The smaller changes are that I’ve used different regulator (a standard 7805) and the NPN transistor I had was ….

It took me a while to track down a “correct” 7segment display (since I didn’t want to mess with the firmware). So I got one from ebay “0.36” 7 Segment LED Display 4 Digit Common Anode” with 2 x 6 pins. The most common ones on ebay have some extra dots on the display - those have more pins.

Final pic to remind me how I actually wired the breadboard version (it’s minusculely different from simpleavr’s, and the regulator is removed so that I can see the wires). The regulator should go like this: ground to black jumper, input to red jumper and output to tiny’s pin 20 / positive lead of the cap. On the breadboard, the 7segment display shares the holes with tiny’s pins on one side.