5. Basic Testing
Once the PCB is assembled and all inspections are successful, it is time to do some basic testing on the board. It would do well to keep in mind that the first prototype will rarely work as expected. In fact the intention of building a prototype is to bring out all the bugs that were not obvious during the design stages. Before you come to a final production worthy version, it is likely that the design goes through several iterations. It is during these iterations that issues are identified, debugged and fixed. It would be a very tricky task to schedule this stage both in terms of cost and time. Ideally we would like the prototype to go through without any bugs identified, but of course the bugs that do crop up are unexpected and isolating the root cause of the issue, and then to devise a strategy to fix it would take time.
Quality control tools like Failure Modes and Effects Analysis (FMEA) is used to predict such failures beforehand and incorporate the fixes in the design before finalizing the hardware design. The intention is to minimize unexpected bugs and other hardware issues during prototyping.
Almost all electronics products would have an on board power supply. It may be in the form of a complex multi topology AC-DC converter, or a simple linear regulator for DC-DC conversion. In the first stage of the testing, the board is powered up and the onboard power supply is evaluated. The output voltages are measured using a multimeter and made sure that they are within the tolerance limits. The engineer can go further and do the following tests which would require testing equipment such as an Oscilloscope.
- Line regulation: This tests the ability of the power supply to maintain its specified output voltage over changes in the input line voltage. It is expressed in percentage of the change in output voltage with respect to the change in the input line voltage.
- Load regulation: This test the ability of the power supply to maintain a constant voltage level on an output channel despite changes in the load.
- Ripple: This tests the presence of small unwanted residual periodic variation of the direct current (DC) output of a power supply, which has been derived from an AC source.
The heart of any embedded system is the processor, and nearly all modern electronic products include a microchip called a Microcontroller, which acts as the master controller for the product. A microcontroller is very similar to a microprocessor that is found on the motherboard of a personal computer, except that the microcontroller has integrated memory and peripherals and hence is more suited for embedded systems. The microcontroller excels in interfacing with various types of sensors and controlling devices such as switches, displays, motors, keypads etc.
The microcontroller has integrated memory and it needs to be programmed with the corresponding firmware to perform the desired functionality. The memory is nonvolatile, but can be reprogrammed. Almost all manufacturers of microcontroller provide a development platform in order to make the development of firmware an easier task. The development platform is customized for the microcontroller of the corresponding manufacturer, so that firmware developed for a microcontroller of a particular manufacturer will not be compatible to a microcontroller of another manufacturer.
Most often, dedicated firmware engineers develop the firmware for the microcontroller, but with knowledge of “C” computer language, the hardware engineer can write simple codes to do some basic testing of the peripherals.
Once the PCB goes through the initial basic testing successfully, the complete firmware can be programmed into the microcontroller and a full-fledged system testing can be performed on the product.
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Enclosure Design
