this hardware can be used on some chips of the same family after slight modification.
uses one ATTiny85 to recover other reset-locked ATtiny85's. Done by bringing the target ATtiny85 into HVSP mode, to reprogram the high fuse bits to 0xDF.
- Kicad 8.0
- master ATTiny85 operates at 8MHz(optional) with reset pin set to act as GPIO(required).
- made from common components. notable exceptions listed.
- the MIC2290 (boost converter IC to supply 12V; ~$1.00 for a order of 1 from Digikey), this can be substituted with a 12V supply tapped to the same trace.
- the USB connector can be substituted with a 5V supply tapped to the same trace.
| Count | Component |
|---|---|
| 1 | MIC2290 boost converter IC |
| 1 | USB A plug |
| 1 | single pole switch (optional) |
| 1 | ATtiny85 |
| 1 | 44.2k Ohm |
| 5 | 5k Ohm |
| 4 | 1.2k ohm |
| 1 | 10uH |
| 1 | 100nF |
| 2 | 10uF |
| 1 | diode (optional) |
| 2 | NPN BJT |
| 2 | PNP BJT |
As shown, empty DIP socket holds target; master has a "dont remove" sticker. 100nF disk has been subsuited with a same sized SMD. 20k ohm pull down added on the buttons low side because the exact button used acts as a ~2M ohm resistor in its off state. Extra solder points because my maufacturing does not support plated vias, manually 'plating' was needed.
- Green: reset-locked chip goes here
- White: go button
- Blue: master chip goes here
- red: 12V control circuitry
- yellow: 5V control circuitry
- fab & assemble board
- program a master ATtiny85 using the code from the 'code' sub folder of this project. note that master ATtiny85 uses its reset pin as GPIO so the approate fuse bit needs set.
- put master in the blue outlined socket; notch to the left.
- put reset-locked ATtiny85 in the green indicated socket; notch to the left.
- press & hold button for ~0.5 seconds
- target chip is now unbricked!