Monitoring LEDs
Integrating LED monitoring on your custom test fixture
Monitoring an LED in Custom Test Fixtures
Does your DUT/UUT have an LED indicator that needs monitoring during testing or alerts the operator about a component? If so, you may need an LED fixture. But how can you monitor an LED if it’s inside a bed-of-nails custom test fixture? Fortunately, there are several ways to achieve this, depending on your needs.
Solutions for LED Monitoring in Test Fixtures
CTS has addressed this issue multiple times and provides various solutions for creating LED fixtures. To determine the best solution, we need to understand the test procedure and budget. If your engineering team decides the LED is essential for the test and cannot be monitored another way, you must also consider the LED’s location during testing.
Common LED Applications in Test Fixtures
A typical LED used in testing is the indicator light on an RJ45 connector. You can integrate these LEDs into board-level test fixtures or final assembly test fixtures.
Simple Solutions for Monitoring LEDs
The simplest solution for many customers is a transparent fixture plate. If the LED is positioned where the operator can easily see it, we leave a window for visual confirmation. However, when probing PCBs from all angles, the LED may end up at the bottom of the unit under test, making visual inspection more challenging. Some customers find that a mirror provides the visual confirmation they need. If this doesn’t work, or if the custom mechanical fixture is inside one of our RF Faraday boxes, we must consider other solutions.
Using a Photo Sensor for Simple LED Monitoring
If the LED reading only needs to be on/off and won’t be blocked by other lights during testing, a simple photo sensor might meet the requirements. We create an isolated area to block ambient light, but tightly grouped LEDs make this confirmation method difficult.
The Most Popular Option: LED Optical Probes
The LED optical probe is the most popular solution. This probe is placed close to the LED to capture light and transmit it through optical fiber to the processor, which then communicates with your PC. Some basic probes are suitable for on/off signals, while others can detect color and intensity. After testing several brands, we recommend the Feasa brand (feasa.ie).
Advanced Solutions for LED Monitoring
When the LED is an integral part of the test, rather than just an indicator, solutions like spectrometers or camera monitoring become necessary. These options are more specialized, so test engineers must identify the most suitable solution.
