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Reanimating Probe for AVR μC Schematic Circuit Diagram

Troubleshooting the “AVR Device Not Responding” Error

Encountering the frustrating message “AVR device not responding” during the programming of your Atmel microcontroller signals the onset of significant challenges. Frequently, this issue stems from incorrect programming of the fuse bits. This is precisely where the unblocking probe becomes invaluable. Once the entire system is powered up, you can effortlessly resolve the problem. With one hand, apply the probe’s tip to the microcontroller’s XTAL1 input, while using your other hand to proceed with programming using your preferred software. In this manner, your microcontroller is effectively rescued from the error.

Reanimating Probe for AVR μC Schematic Circuit Diagram

Designing a Cost-Effective Oscillator Circuit

The primary objective in crafting these electronics was simplicity, aiming for an affordable and easily replicable design. The core component is an oscillator generating a rectangular wave at approximately 500 kHz, constructed using a 74HC04 IC. Although the circuit works with a 74HC14, the frequency might slightly vary (around ±50 kHz) based on the specific IC brand. However, this frequency difference does not impact the probe’s functionality.

Connection Setup with Unblocking Board

The unblocking board is linked using a ribbon cable, terminating with two female HE10/10 connectors. The pinout configuration of the HE10/10 connector aligns with the majority of circuits, but it can be adjusted to fit an HE10/06 connector if necessary.

The initial connector establishes a connection with the board to be unblocked, facilitating the power supply to the electronics. The second connector is linked to the ISP programmer (STK200 compatible). The crystal contact is made using a needle, ensuring consistent contact even through a varnished board. Notably, there’s no requirement to desolder the crystal during this operation.

Accessibility of PCB Design Files

The design files for the PCB, available in Eagle format, can be accessed from [1]. This resource provides the necessary information for replicating the circuit, allowing enthusiasts to recreate the unblocking probe efficiently.

Internet Link
[1] www.elektor.com/110374

The 74HC14; 74HCT14 is a hex inverter with Schmitt-trigger inputs. This device features reduced input threshold levels to allow interfacing with TTL logic levels. Inputs also include clamp diodes, this enables the use of current limiting resistors to interface inputs to voltages in excess of V CC.


  • Output Drive Capability: 10 LSTTL Loads
  • Outputs Directly Interface to CMOS, NMOS, and TTL
  • Operating Voltage Range: 2.0 to 6.0 V
  • Low Input Current: 1.0 A
  • High Noise Immunity Characteristic of CMOS Devices
  • In Compliance With the JEDEC Standard No. 7A Requirements
  • ESD Performance: HBM 2000 V; Machine Model 200 V
  • Chip Complexity: 60 FETs or 15 Equivalent Gates
  • These are Pb−Free Devices

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