Engineer Tim faced a significant challenge: vintage discrete logic components from the 1950s and 1960s were becoming impossible to source reliably. Rather than abandon discrete logic design, Tim developed Analog Multiplexer Logic (AML), a novel approach using readily available analog multiplexer integrated circuits.[1][2][3][4]
Tim Solves Vintage Component Crisis With Innovative Approach
His innovation addresses a critical problem in modern electronics: resistor-transistor logic (RTL) and diode-transistor logic (DTL) components are increasingly scarce, expensive, and geographically inconsistent. Tim’s solution enables complete digital logic gate implementation using affordable, widely-available components.[5][6][7][8]
From Concept to Implementation: Tim’s Development Journey
Tim began exploring AML through SPICE circuit simulations based on established logic principles. His goal was to synthesize hardware description language (HDL) code into discrete logic PCB layouts through a project called PCBFlow.[4]
His first prototype failed, returning nonfunctional results. Rather than abandon the approach, Tim refined the design, analyzing what went wrong and optimizing the circuit topology.[4]
Tim’s second attempt succeeded, producing robust logic operating reliably at clock speeds up to 15 MHz, limited only by his function generator’s specifications. This performance breakthrough validated his methodology.[4]
Tim also explored a variant design using G175 single-gate D-Flipflops to increase circuit density further, demonstrating the technique’s flexibility and scalability.[4]
Why Tim Chose Analog Multiplexers Over Traditional Discrete Transistors
Tim recognized that analog multiplexers offered distinct advantages over bipolar switching transistor logic:
- Faster operation than traditional discrete transistor designs[4]
- Readily available components from multiple manufacturers[9][10]
- Modern documentation and datasheets available globally[11]
- Cost-effective alternative to searching for obsolete vintage logic[12]
- Proven performance up to 15 MHz in his implementation[4]
Tim’s work particularly appeals to hobbyists, students, and engineers seeking discrete logic solutions faster than traditional transistor circuits but without pursuing rare vintage components.[4]
The Technical Foundation: CD4052 Specifications
Tim’s AML design uses analog multiplexer integrated circuits, particularly the CD4052 differential 4-channel multiplexer:
| Specification | Value |
|---|---|
| ON resistance | 80Ω typical[13] |
| Signal capability | ±5V to ±15V range[13] |
| Supply voltage | ±5V to ±7.5V (symmetric)[14] |
| Propagation delay | ~125 nanoseconds[15] |
| Manufacturers | NXP, Fairchild, others[16] |
Analog multiplexers operate transistor switches in linear mode, enabling voltage routing based on input combinations to create logic gates.[17][18]
Debugging the First Prototype: Learning From Failure
Tim’s initial implementation exhibited unintended oscillation in SR latch circuits. This critical failure revealed an important design principle: reversed feedback polarity converts negative feedback (stabilizing) into positive feedback (oscillating).[19][20][4]
After identifying the root cause “polarity error in feedback paths” Tim redesigned the circuit with simplified topology and optimized component values, achieving stable operation in his second attempt.[4]
Contribution to the Maker Community
Tim submitted his work to Hackaday’s 2025 Component Abuse Challenge, positioning AML as a practical alternative for the discrete logic community. His documentation and schematics provide valuable reference material for electronics enthusiasts exploring unconventional logic implementations.[21][4]
The Hackaday community, particularly the TTL enthusiast network, recognized the contribution’s value for modern discrete logic projects where component sourcing presents ongoing challenges.[22][23]
Performance Limits and Future Potential
Tim’s implementation achieved 15 MHz operation, representing the test equipment ceiling rather than circuit maximum capability. CMOS propagation delays of 100–200 nanoseconds support realistic operating frequencies in the 5–15 MHz practical range for discrete logic applications.[15][4]
This performance spectrum addresses educational applications, sensor processing, and microcontroller interfacing scenarios where vintage logic components are unnecessary and unavailable.[4]
