Chapter 299: Hardware Certification Processes

Chapter Objectives

By the end of this chapter, you will be able to:

• Describe the end-to-end process of taking a product through official hardware certification.
• Identify the key players in the certification ecosystem: the test lab, the TCB, and the manufacturer.
• Understand the difference between pre-compliance, conducted, and radiated testing.
• Develop specialized “test mode” firmware to allow a test lab to control the device’s radio functions.
• Use ESP-IDF APIs to set specific channels, transmit modes (like continuous wave), and power levels.
• List the typical documentation and hardware samples required for a certification submission.

Introduction

In the previous chapter, we explored the “what” and “why” of regulatory compliance, understanding the rules and standards that govern electronic products. Now, we turn to the “how.” How do you actually prove to the authorities in the US, Europe, and beyond that your new ESP32-based product meets these standards? The answer lies in a formal, structured engagement with a series of independent bodies in a process known as hardware certification.

This process transforms your prototype from a lab curiosity into a legally marketable product. It involves meticulous preparation, specialized software, and close collaboration with accredited test laboratories. As a firmware developer, your role is not peripheral; it is central. You will be responsible for creating the specific firmware that allows the lab’s engineers to put your device through its paces.

This chapter provides a practical roadmap for this journey. We will walk through the steps, define the key players, and show you how to write the essential test-mode firmware that makes certification possible.

Theory

The certification process is a formal verification exercise conducted by independent, accredited organizations. You, as the manufacturer, must provide them with everything they need to prove your product’s compliance.

1. The Key Players

There are three main roles in the certification ecosystem:

1. The Manufacturer (You): The company or individual responsible for the product design, manufacturing, and for declaring its compliance. You initiate the process, pay for the testing, and are legally responsible for the final product.
2. The Accredited Test Laboratory: An independent company with highly specialized equipment (like anechoic chambers) and trained personnel. Their job is to perform the actual tests according to the required standards (e.g., FCC Part 15, ETSI EN 300 328) and produce a detailed, factual test report. They provide the evidence; they do not grant the certification itself.
3. The Certification Body (TCB or Notified Body):
   • In the US, this is a Telecommunication Certification Body (TCB), a company authorized by the FCC to review test reports and officially grant an FCC certification and ID number.
   • In the EU, this is a Notified Body, an organization designated by a member state to assess conformity with the CE directives (like RED). While a Notified Body’s involvement is not always mandatory for CE marking (sometimes a manufacturer’s self-declaration is sufficient), using one is common practice for complex radio equipment.

graph TD
    subgraph "Certification Flow"
    A("<b>1. Manufacturer</b><br><i>(You)</i>")
    B(<b>2. Accredited Test Lab</b>)
    C(<b>3. TCB / Notified Body</b>)
    
    A -- "Sends Samples & Documentation" --> B
    B -- "Performs Tests" --> B
    B -- "Provides Test Report" --> A
    A -- "Submits Application & Test Report" --> C
    C -- "Reviews & Issues Grant" --> A
    end

    classDef manufacturer fill:#EDE9FE,stroke:#5B21B6,stroke-width:2px,color:#5B21B6
    classDef lab fill:#DBEAFE,stroke:#2563EB,stroke-width:1px,color:#1E40AF
    classDef body fill:#D1FAE5,stroke:#059669,stroke-width:2px,color:#065F46
    
    class A manufacturer
    class B lab
    class C body

2. The Certification Process Flow

The journey from prototype to certified product follows a standard path.

1. Engage a Test Lab: The first step is to contact and get quotes from one or more accredited labs. They will be your primary technical partner through the process.
2. Pre-Compliance Testing (Optional but Recommended): Before committing to the full, expensive formal testing, it’s wise to do a “pre-compliance” run. This is a shorter, less formal set of tests to catch any obvious problems early. It’s much cheaper to discover and fix an EMC emissions problem at this stage.
3. Prepare the Test Package: You must provide the lab with a set of materials:
   • Test Samples: Typically 2-3 identical units of your final production hardware. One may be modified for “conducted” tests.
   • Test-Mode Firmware: Special firmware that gives the lab control over the radio. (More on this below).
   • Detailed Documentation: This includes schematics, a bill of materials (BOM), block diagrams, user manuals, and antenna specifications.
4. Formal Testing: This is where the core work happens.
   • Conducted Tests: A test sample is modified so its antenna is disconnected and a temporary RF connector is added. This connector is plugged directly into the lab’s spectrum analyzers. This allows them to measure the “pure” signal coming from the ESP32’s radio without any influence from the antenna, measuring things like power levels, channel bandwidth, and spurious emissions.
   • Radiated Tests: An unmodified sample, complete with its antenna, is placed in a special RF-shielded, echo-absorbing room called an anechoic chamber. The lab uses antennas to measure what your device actually transmits into the air. This measures the final system’s performance, including antenna efficiency and radiated spurious emissions.
5. Review and Submission: The lab provides you with a detailed test report (which can be hundreds of pages long). If the device passed, you (or the lab on your behalf) submit this report, along with your application documents, to a TCB.
6. Certification Grant: The TCB reviews the entire package. If everything is in order, they issue the official Grant of Certification and, for the FCC, publish the new FCC ID in their public database. Your product is now certified.

graph TD
    A(<b>Start: Engage Test Lab</b>) --> B{"<b>Pre-Compliance Testing?</b><br><i>(Recommended)</i>"};
    B -- "Yes" --> C(<b>Perform Pre-Compliance Tests</b>);
    C --> D{<b>Pass?</b>};
    D -- "No" --> E(<b>Fix Issues & Redesign</b>);
    E --> C;
    
    B -- "No" --> F;
    D -- "Yes" --> F(<b>Prepare Formal Test Package</b><br>- Test Samples<br>- Test-Mode Firmware<br>- Documentation);
    
    F --> G(<b>Formal Testing at Lab</b><br>- Conducted Tests<br>- Radiated Tests);
    G --> H{<b>Pass All Formal Tests?</b>};
    
    H -- "No" --> E;
    H -- "Yes" --> I(<b>Submit Report to TCB/Notified Body</b>);
    I --> J((<b>Receive Certification Grant!</b><br>Product is Market-Ready));

    classDef start fill:#EDE9FE,stroke:#5B21B6,stroke-width:2px,color:#5B21B6
    classDef decision fill:#FEF3C7,stroke:#D97706,stroke-width:1px,color:#92400E
    classDef process fill:#DBEAFE,stroke:#2563EB,stroke-width:1px,color:#1E40AF
    classDef check fill:#FEE2E2,stroke:#DC2626,stroke-width:1px,color:#991B1B
    classDef success fill:#D1FAE5,stroke:#059669,stroke-width:2px,color:#065F46

    class A,J start
    class B,D,H decision
    class C,E,F,G,I process

3. “Test Mode” Firmware: Your Key Contribution

Normal application firmware is useless to a test lab. They cannot wait for the device to connect to Wi-Fi to measure a signal. They need direct, low-level control of the radio. Therefore, you must provide a special firmware binary that can, on command, perform specific RF test functions.

The key functions required are:

• Continuous Wave (CW) Transmission: Transmit a pure, unmodulated sine wave at a specific frequency (channel). This is used to easily find the fundamental frequency and measure its power.
• Modulated Transmission: Transmit a normal, modulated Wi-Fi or Bluetooth signal, but continuously and on a fixed channel and data rate.
• Set Channel: Command the device to switch to any channel in the band (e.g., Wi-Fi channel 1, 6, or 11).
• Set TX Power: Command the device to transmit at a specific power level.

Typically, this test firmware is controlled via a simple command-line interface over a UART serial connection.

Practical Example: Building a Basic Test-Mode Firmware

Let’s create a simple test firmware that provides some of the key functions a lab would need, controlled via the serial monitor.

Tip: Espressif provides a more comprehensive “Manufacturing Utility” and other tools that expose these features. However, understanding the underlying ESP-IDF APIs is invaluable for debugging and customization.

The Code

This application will start a simple command loop. When the lab engineer types a command into the serial console, the firmware will configure the radio accordingly.

#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_wifi.h"
#include "esp_log.h"
#include "esp_event.h"
#include "nvs_flash.h"
#include "driver/uart.h"
#include <string.h>

static const char *TAG = "TEST_MODE";

// Test functions provided by esp_wifi library
extern esp_err_t esp_wifi_test_tx_cw(uint8_t channel, uint8_t power);
extern esp_err_t esp_wifi_test_stop(void);

void command_loop_task(void *pvParameters) {
    char cmd[64];
    int len;

    ESP_LOGI(TAG, "Ready for test commands (e.g., 'cw 6 78', 'stop')");

    while (1) {
        len = uart_read_bytes(UART_NUM_0, (uint8_t*)cmd, sizeof(cmd) - 1, pdMS_TO_TICKS(1000));
        if (len > 0) {
            cmd[len] = '\0';
            ESP_LOGI(TAG, "Received command: %s", cmd);

            // --- Parse Commands ---
            char *token = strtok(cmd, " \r\n");
            
            if (token != NULL && strcmp(token, "cw") == 0) {
                // Command: cw [channel] [power_qdbm]
                // Example: "cw 6 80" -> Transmit CW on channel 6 at 20dBm
                char *ch_str = strtok(NULL, " \r\n");
                char *pwr_str = strtok(NULL, " \r\n");
                if (ch_str && pwr_str) {
                    uint8_t channel = atoi(ch_str);
                    uint8_t power = atoi(pwr_str);
                    ESP_LOGW(TAG, "Starting CW TX on channel %d, power %d", channel, power);
                    esp_wifi_test_tx_cw(channel, power);
                }
            } else if (token != NULL && strcmp(token, "stop") == 0) {
                // Command: stop
                ESP_LOGW(TAG, "Stopping all RF tests");
                esp_wifi_test_stop();
            } else {
                ESP_LOGE(TAG, "Unknown command");
            }
        }
    }
}

void app_main(void) {
    // Basic initializations
    ESP_ERROR_CHECK(nvs_flash_init());
    ESP_ERROR_CHECK(esp_netif_init());
    ESP_ERROR_CHECK(esp_event_loop_create_default());

    // --- Critical for Test Mode ---
    // Initialize Wi-Fi but do NOT start it in station or AP mode.
    // We only need the driver to be active to access the test functions.
    wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
    ESP_ERROR_CHECK(esp_wifi_init(&cfg));
    ESP_ERROR_CHECK(esp_wifi_set_mode(WIFI_MODE_NULL)); // Set to NULL mode
    ESP_ERROR_CHECK(esp_wifi_start());
    
    // Disable Wi-Fi power save for consistent test results
    ESP_ERROR_CHECK(esp_wifi_set_ps(WIFI_PS_NONE));

    xTaskCreate(command_loop_task, "cmd_loop", 4096, NULL, 5, NULL);
}

Instructions

1. Build and flash this firmware onto a test sample.
2. Connect to the serial monitor. You will see the “Ready for test commands” prompt.
3. Type cw 6 80 and press Enter. The device will begin transmitting a continuous wave on Wi-Fi channel 6. The lab engineer would now use their spectrum analyzer to measure this signal.
4. Type stop and press Enter. The transmission will cease.
5. This simple interface is the basis of what you would provide to a test lab. A real version would include commands for modulated TX, setting data rates, and testing Bluetooth as well.

Variant Notes

• Test Functions are Variant-Aware: The underlying test functions (esp_wifi_test_...) are implemented differently for each variant, but the API presented to you is generally consistent. You write the same code, and the driver handles the low-level hardware differences.
• Complex Radio Testing: Certifying a device with multiple radios is more complex.
  • ESP32-S3 (Dual-Band Wi-Fi): The test plan must include tests for both the 2.4GHz and 5GHz bands. Your test firmware must be able to accept commands to switch between these bands.
  • ESP32-C6 (Wi-Fi 6 + 802.15.4): The lab must test Wi-Fi, Bluetooth LE, and the 802.15.4 (Thread/Zigbee) radio. Each protocol has its own set of test cases. Your firmware will need separate command handlers for each radio. For example wifi_tx_chan 6 vs ieee802154_tx_chan 15.
• Conducted Sample Preparation: Creating the conducted test sample (with the U.FL connector) can be more difficult on smaller modules (like those for the C-series or S-series) due to their compact size. This is usually handled by the lab or a skilled technician.

Common Mistakes & Troubleshooting Tips

Exercises

1. Expanded Test Firmware: Extend the practical example. Add a new command, tx_mod, that takes channel, power, and data rate as arguments. It should use the esp_wifi_80211_tx() function to send a continuous stream of modulated Wi-Fi packets. This simulates the other major test mode required by labs.
2. Lab Research and RFQ: Identify two accredited test labs in your country/region. Find their websites and look for their contact information for requesting a quote (RFQ). Draft a mock email RFQ for your ESP32 weather station project. You should specify that it uses a pre-certified ESP32-WROOM-32E module and that you need pricing for FCC and CE certification. This simulates a real-world first step in the process.

Summary

• The hardware certification process involves three key players: the Manufacturer (you), the Test Lab, and the Certification Body (TCB/Notified Body).
• The process moves from preparation and pre-compliance to formal testing, which includes conducted (direct connection) and radiated (over-the-air) measurements.
• The firmware developer’s most critical contribution is the test-mode firmware, which provides direct, low-level control over the device’s radios for the lab engineers.
• Proper preparation, including stable hardware samples, comprehensive documentation, and well-tested firmware, is essential to ensure a smooth and cost-effective certification experience.
• Every ESP32 variant and module combination has its own unique certification, and more complex radios require more extensive test plans.

Further Reading

• Espressif Manufacturing and Test Tools Documentation: https://docs.espressif.com/projects/esp-test-tools/en/latest/esp32/index.html (This is a great starting point for more advanced test tool features).
• An Overview of the FCC Authorization Process for RF Equipment: https://www.fcc.gov/oet/ea/rfdevice