$5 ESP32-C3 Blocks 537,000 Ad Domains: What It Signals
20 Jul 2026
A full-stack developer going by ZedAxis has turned a $5 microcontroller into a surprisingly capable ad-blocking appliance — and the engineering behind it offers a small but instructive case study for founders eyeing low-cost embedded hardware.
What was built
ZedAxis, an Egyptian developer, built a backup DNS filter using an ESP32-C3 SuperMini board to keep ad-blocking active on his home network whenever his primary Pi-Hole was rebooting or otherwise unavailable. Tom's Hardware reported on the finished device, detailing its capacity, memory footprint, and latency.
The headline number: the $5 board can store up to 537,000 blocked domains — all while drawing just a few dozen milliamps of power and resolving blocked lookups in roughly 10ms.
The engineering tradeoffs
The ESP32-C3 chip has modest specs — 400KB of RAM and 4MB of flash — yet the finished firmware uses only about 50KB of RAM to manage blocked lookups. ZedAxis achieved this density using 40-bit FNV-1a hashes to store domain data, explaining that 32-bit hashes caused too many collisions while 64-bit hashes wasted too much space. The 40-bit middle ground appears to be the key to fitting hundreds of thousands of domains into a chip this small.
Capacity also depends on a tradeoff with update mechanisms: with OTA (over-the-air) firmware updates enabled, the device can hold about 250,000 domains. Disabling OTA support frees up enough space to push that number to 537,000 — but the report notes this leaves the firmware without a remote update mechanism, potentially requiring manual reflashing to change the blocklist.
What's still unclear
The report leaves several open questions: how the domain blocklist itself is sourced or updated when OTA is disabled, how this device's performance or coverage compares to a full Pi-Hole setup, the exact specs of the SuperMini board beyond RAM and flash, and whether ZedAxis intends to open-source or productize the project.
Why founders should care
This is a hobbyist project, not a funded startup — but it's a useful signal for anyone building networking or IoT hardware:
- Memory-efficiency tricks likely matter more than raw specs. The use of 40-bit hashing to compress hundreds of thousands of domains into ~50KB of RAM suggests founders building on resource-constrained microcontrollers may find meaningful headroom through smarter data structures rather than pricier chips.
- Sub-$5 hardware may be increasingly viable for niche privacy/networking tools. If a $5 board can plausibly serve as a dedicated ad-blocking backup, founders exploring low-cost dedicated hardware (as opposed to software-only or general-purpose devices) may want to evaluate whether similar chips fit their product roadmap.
- OTA-vs-capacity tradeoffs deserve early product decisions. Teams building embedded devices with fixed blocklists, rules, or config data may need to decide early whether remote-update capability is worth the capacity cost — a decision that likely affects both user experience and support overhead (e.g., manual reflashing).
Overall, the project is too early-stage and undocumented to draw firm market conclusions, but it does illustrate that ultra-low-cost microcontrollers can plausibly support real DNS-filtering workloads — a data point worth filing away for founders in edge networking, IoT, or privacy hardware.