Testing the CheapBot-14 In six easy steps These six tests verify that your robot controller was assembled correctly. The CheapBot-14 v2.0 PCB is covered in resist masking, so it is difficult to short out components. In addition, the top silk indicates the proper orientation and placement of components. So most likely, your robot controller is just fine. But is always pays to double check. There should be no batteries and no microcontroller in the robot controller at this time. As you proceed through the check steps, you will eventually insert the batteries and microcontroller.

Inspect the Bottom of the PCB Look for bad solder joints The first step is to flip your PCB over and look at the solders. A good solder looks like a little cone around the solder pad and wire. If the solder looks good, but the lead is long, then trim the lead. The lead should end at the top of the solder. If the solder is a ball, then the solder pad did not get hot enough during soldering. Add fresh solder to the tip of a soldering iron and reheat the solder. When the pad gets hot enough, the molten solder will flow into contact wit the pad. If the solder does not form a complete cone around the lead, then there is a possibility that the lead is not fully electrically and mechanically connected to the pad. A bad connection like this may fail at unpredictable times, making the robot’s operation intermittent. To fix an incomplete solder, apply fresh solder to the tip of a soldering iron and reheat the solder and pad. Once the pad is hot enough, the molten solder will flow into contact with the pad, all away around the pad.

Inspect the Bottom of the PCB Look for overflow Next look for solders that have overflowed their solder pad. If two pads are close together, but not on the same trace, then an overflow can create a short circuit. The best way to fix an overflow is with solder ribbon. Lay a piece of solder ribbon above the overflow and heat it from above with a well-tinned soldering iron. The hot solder ribbon will absorb the molten solder below it. Alternatively, you can try to brush the overflow away with a hot soldering iron. Apply a soldering iron to the overflow area and let the solder melt. Once molten, then whisk the soldering iron over the pool of liquid solder to try to break it up.

Check for a Short in the Battery Pack After the solders beneath the PCB are verified to be in good shape its time to test the robot controller with a digital multimeter. The first test is to verify that there is no short in the battery pack. If there is one, then the batteries will short out when snapped into their battery holder. That’s bad news and will cause the batteries to get hot. They may even begin leaking. Set a multimeter to measure continuity or low resistance. Apply the test leads to the positive and negative terminals of the battery pack. The resistance between the two terminals should be very high, in the thousands of ohms or higher. In continuity mode, the multimeter should not ring.

Check for a Short Onboard the Robot Controller After checking for shorts outside the robot controller, its time to check for shorts onboard the robot controller. The most accessible location is on the second and third pins of the voltage regulator. Set a multimeter to measure continuity or resistance and tap the center and right leads of the voltage regulator. There should be no continuity or the resistance should be very high, like in the thousands of ohms.

Check for Five Volts on the PICAXE IC Socket If the logic power switch is in the ON position, switch it off. Now insert batteries into the logic battery pack. When you flip the switch, the power LED should illuminate. That verifies that parts of the robot controller are receiving power. The next step is to verify that the microcontroller will be supplied with five volts. Set the multimeter to voltage. If the multimeter is not autoranging, then set the range to 20 volts. Tap the multimeter’s red lead to pin #1 of the IC socket and the common lead to pin #14 of the IC socket. The multimeter should display a voltage between 4.75 V and 5.25 V.

Check that the PICAXE can be Programmed PAUSE 500 DEBUG Switch off power to the robot controller. Before snapping the PICAXE-14M2 into the IC socket, verify two things. First, the leads of the microcontroller may be a little too spread out to fit the IC socket. You may need to give them a little squeeze to make them more vertical. Second, recall that the IC socket was soldered according to the pattern of the PCB’s top silk. That means the notch in the IC socket was aligned with the square drawn into the top silk. As long as this is true, then the notch in the PICAXE-14M2 will align with the notch in the IC socket. Place the microcontroller on the top of the IC socket and align all the pins. Now place your finger over the center of the PICAXE and press down firmly. The IC should pop into the IC socket. Now its time to write your first program. Start the Editor and set the Mode to PICAXE-14M2 and the proper serial port. Then write the following program and download it. PAUSE 500 DEBUG After downloading, the Debug window should pop up and sow that all the memory addresses are zeros. If you made it this far, then your CheapBot-14 checks out.