Back to setup circuit

When your circuit is not working, you should check your hardware setup. Here are some steps to follow:

• Step1: Check your circuit schematic and make sure it does what you what it to do. Your circuit is doing what it supposes to do following the physical law. IT IS ​IMPOSSIBLE​ TO EFFECTIVELY DEBUG A CIRCUIT IF YOU DO NOT UNDERSTAND ITS SCHEMATIC AND DO NOT KNOW HOW IT IS SUPPOSED TO WORK.
• ­Step2: Know what is happening. Obvious, your circuit is not doing what you want it to do. But it is doing something. You can use your multimeter to measure the resistance, voltage and sometime even current across your circuit.
• Step3: Know why it is happening.  Once you figure out what is happening in your circuit. Think about what might cause this happen.  A zero resistance across part of circuit suggest short. High resistance across a wire suggests that the wire is broken. Guesses are fine here. Make a mental list of potential cause, or even write them down if that helps.
• Step4: Testing the possible cause one by one and fix it. Following the list, cross them off one-by-one by testing the possible cause. Measure the power supply, test/replace the motor, measure the resistance between the output and ground, calculate the output current you need and check the datasheet to see if the components can handle it. Slowly you will uncover the truth.

common circuits problems list:

• Always Check First
  ○ Is the power supply on?
  ○ Is your oscilloscope settings correct? (AKA is there actually a problem?)
  ○ Do you understand the schematic?
  ○ Did you build it correctly?
  ○ DO YOU UNDERSTAND THE SCHEMATIC?
  ○ DID YOU BUILD IT CORRECTLY?
• Oscilloscope / Test Equipment Issues
  ○ Are you triggering properly?
  ○ Are you in in the correct AC/DC mode?
  ○ Are you at the appropriate zoom level in time and amplitude?
  ○ Is your trace offset centered at zero?
  ○ Is your probe ground clip connected to ground? (Do This)
  ○ Are multiple probe ground clips tied to different voltages? (DON’T DO THIS)
  ○ Is your scope and probe on 10x mode?
  ○ Did you check/calibrate the scope probes?
  ○ Is your function generator in High Z mode?
  ○ Is the output button on the function generator green? (Is it outputting a signal?)
• Device/ Integrated Circuit (IC) Issues
  ○ Are all of your IC’s powered? (Power pins tied to ground and/or supply voltages)
  ○ What is the quiescent operating point (i.e., with no inputs)?
  ○ Did you read the datasheet / understand how to use the device/ IC?
  ○ Can your device / IC even do the desired operation? (Is it fast enough?)
  ○ Is the device/ IC plugged in correctly? (It is easy to plug them in upside down)
  ○ Do you have any floating IC pins that should be tied to something
  ■ Only pins labeled “not connected” should be left floating; you must watch out for pesky enable pins that must be tied to the correct voltage.
  ○ Did you accidentally destroy the IC/Device?
  ■ Common for circuits involving a lot of power.
  ■ Check circuit to make sure replacement won’t also be destroyed.
  ○ Did you use the recommended configuration for your application that is sometimes specified in the datasheet.
  ■ It is very common for sensor datasheets to specify a schematic, use it.
• Construction Issues
  ○ Is there a bad breadboard connection? (a very short wire that goes into the hole but doesn’t make contact)
  ○ Some breadboards have split power rails, make sure the entire rail is connected.
  ○ Is there a short between neighboring breadboard rails? (Sometimes happens)
  ○ Do you have any broken connections / parts?
  ○ Do you have a bad solder connection?
  ○ Do you have solder bridge? (a short caused by solder connecting adjacent pins)
  ○ Are two wires touching that shouldn’t be? (Avoid by building neat circuits)
• General Issues
  ○ Are the power rails at the correct voltages?
  ■ If not, you might be drawing too much power.
  ○ Check your DC voltages. Do they make sense?
  ○ Did you check for shorts using the multimeter’s continuous mode?
  ○ Are you trying to drive the same node to multiple voltages?
  ■ This occurs when you connect the output of two buffers directly together.
  ○ Check the input­ output relationship of your sub­modules independent of each other.
  ○ Are your components the correct size?
  ■ accidentally using a 100 Ohm instead of a 100k Ohm resistor is common and will certainly cause problems.