ZX Spectrum Transforms into a Z80 Frequency Counter for the 2025 One-Hertz Challenge
The ZX Spectrum, a beloved home computer and games machine from the 80s, has been creatively repurposed as a frequency counter in an innovative project for the 2025 Hackaday One Hertz Challenge. This project showcases the versatility of retrocomputing and the ongoing interest in repurposing vintage hardware for modern applications.
The frequency counter uses the EAR port of the ZX Spectrum to input a signal and count its rising edges over a period of one second. This method allows for the direct determination of the frequency of the input signal. The project is achieved through the use of assembly coding techniques, utilising the Z80 processor's capabilities to manage the timing and edge detection.
Here's an overview of how it works and the assembly coding steps involved:
**How It Works**
1. **Signal Input**: The frequency counter uses the EAR port of the ZX Spectrum to input a signal. This port is typically used for audio output but can be repurposed for other tasks.
2. **Edge Counting**: The assembly code counts the rising edges of the input signal over a one-second interval. This count directly corresponds to the frequency of the input signal.
3. **Frequency Determination**: By summing the rising edges within the one-second window, the code calculates the frequency. This method is straightforward and efficient for measuring frequencies up to a certain range.
**Assembly Coding Steps**
While the specific assembly code is available on GitHub, the general steps involve:
1. **Initialization**: Set up the ZX Spectrum's Z80 processor to access the EAR port for input, and initialize any necessary variables or registers for counting and timing.
2. **Timer Setup**: Use the Z80's timer or a software timer to manage a one-second interval during which the rising edges are counted. Ensure the timer accurately triggers at the start and end of each second.
3. **Edge Detection**: Monitor the EAR port for rising edges within the one-second window. Increment a counter each time a rising edge is detected.
4. **Frequency Calculation**: Once the one-second period ends, calculate the frequency by using the total count of rising edges. Store the result for display or further processing.
5. **Display and Repeat**: Output the calculated frequency, either directly on the ZX Spectrum's display or through a connected device. Repeat the process continuously to provide real-time frequency readings.
This project, created by an individual named [Tito], demonstrates the potential of retrocomputing and serves as an opportunity to exercise assembly coding skills. The frequency counter is eligible for entry in the 2025 One Hertz Challenge due to its one-second period, and it is capable of reading frequencies up to 20 KHz. However, it might not be ideal for reading faster signals.
For those interested in retrocomputer hacks, feel free to share your projects. The code for the frequency counter is available on Github for reference. Similar projects have been done before, showcasing the ongoing interest in repurposing vintage hardware.
The frequency counter in the innovative project is built using the EAR port of the ZX Spectrum as a signal input and relies on the Z80 processor's capabilities for edge counting, timing, and assembly coding techniques. This demonstration of technology's versatility underscores the ongoing fascination with repurposing vintage hardware for modern applications in the field of retrocomputing.
