![]() Hard drives and SD cards are another common failure point. If the POST tests succeed, the next step is for the computer to boot into its operating system, which is held on the long-term storage device. Or if not, it will indicate what’s wrong and you can try replacing those components. ![]() The Raspberry PI Model B+ also has an HDMI port, and many times my students are surprised to realize that you can plug in a monitor and keyboard and suddenly their quadrotor drone is a PC! Once you’ve verified the POST ran, you can be fairly confident the CPU, motherboard, and RAM are working. Most robots support this somehow for example our MOVO robot has an HDMI port on the bag to plug into. The BIOS beep codes and LED flashes indicate problems without needing a monitor, but plugging in a monitor will show exactly what’s going on. This may already be true if you are working with a PC, but if you are working with a robot, it may not have a monitor plugged in by default. Of course, the best way to get more information about what’s going on with the POST is to plug in a monitor and keyboard into the computer. The Raspberry PI doesn’t have beep codes instead it has LED flash codes to indicate different errors. Then the documentation for the BIOS will indicate what the beep codes mean. This requires figuring out exactly which BIOS you have by looking up the specifications for that PC, or opening it up to look at the motherboard. ![]() A PC that fails its post will make strange BIOS beep codes, and you need to figure out what the beep codes mean. It verifies that each of the hardware components of the machine are working. This POST occurs immediately after powering on, before you boot into your operating system (which requires access to long-term storage). Once a computer is powered on, it conducts a power-on self-test (POST). However it is next in the debugging process because it is necessary for checking if your long-term storage system is working. The compute subsystem fails less frequently than the other two. One useful way to quickly check for this is the “smell test”: if the inside of your robot smells slightly smokey or burned, you most likely had a short and should look for something that looks burned.Ĭompute Subystem. In this case, you’ll most likely need to replace a fuse, wire, etc. It’s also possible a short-circuit has occurred, and something is fried. Don’t forget to check the wall! Maybe the wall outlet isn’t receiving power, and your robot is fine. For example, here is the information on the voltages required to power the Raspberry Pi. You might have to take the device apart to access the power supply you might have to do some digging to find the data sheet. If you can’t verify power is coming to the device, get a multimeter and check that the voltage coming from the battery or power supply is what is specified in the datasheet. For example, the Raspberry Pi Model B+ has two LEDs, labeled ACT (activity) and PWD (Power), which you can see in this picture. (Batteries have a limited number of charging cycles they wear out and need to be replaced!) Most robots or devices have some kind of LED that indicates that power is being transmitted to the device, and the location, color, and meanings of these LEDs is often documented in the device spec sheet or on the board itself. This could be because the power supply failed, because the battery died, or maybe your wall outlet doesn’t have power. The most common symptom of a power problem is that the robot or device just won’t turn on. Be careful with unscrewing, you don’t want to strip the screws. When doing this, be sure to keep track of all the pieces you unscrew, and it’s always good to have backups in case. You should always wear an antistatic wrist strap when fixing power systems to ensure you don’t discharge any static into the robot. static charge can build on you, which is dangerous when getting near power systems to fix them. Pieces can be very fragile and delicate and aren’t made for outside conditions. If you are pulling your robot apart and see a lot of dust, take a second to clear it out! Also, always make sure that when fixing your robot and the power is on, that you are near the e-stop. While it is rarely the case, it is possible that dust build-up inside your robot is causing ventilation issues. Sometimes it is necessary to take the robot apart to check these subsystems. You want to therefore systematically check each subsystem (in that order) to verify that it is working correctly. The hardware subsystems that most commonly fail are 1) the power subsystem 2) the compute subsystem (RAM/CPU/motherboard 3) the long-term storage subsystem (hard drive or SD card). The first step is to determine if the hardware itself is working. Since robots are computers, many of the steps also apply to fixing a broken phone, tablet or PC, although the details differ. This post describes steps for fixing a robot that is broken.
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