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Breadboards, Multimeters, and Resistors

Breadboards, Multimeters, and Resistors. EGR1301. Your Multimeter. pincer clips – good for working with Boe-Bot wiring. probes. (push these onto probes). leads. turn knob to what you would like to measure. You will use the multimeter to understand and troubleshoot circuits, mostly

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Breadboards, Multimeters, and Resistors

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  1. Breadboards, Multimeters, and Resistors EGR1301

  2. Your Multimeter pincer clips – good for working with Boe-Bot wiring probes (push these onto probes) leads turn knob to what you would like to measure You will use the multimeter to understand and troubleshoot circuits, mostly measuring DC voltage, resistance and DC current.

  3. Measure Vin Vin will be the same as your power supply voltage. For the case below, 4 AA batteries are used resulting in approximately 6 V (5.79 V to be more exact). Vin = power supply voltage Vss = ground (negative side of battery) Switch to DC Volts

  4. Measure Vdd Vdd will always be around 5V (it is 4.94 V here). A voltage regulator on the Board of Education reduces this voltage from Vin down to ~ 5V. The Boe-Bot operates on 5V DC. Vdd ~ 5V Vss = ground (negative side of battery)

  5. Build the Series Circuit Below 5V + - 220W 470W the breadboard connects these resistors

  6. Select Resistors Find the 220W and the 470W resistors from your Boe-Bot kit. Example: 470W resistor: 4 = yellow 7 = violet Add 1 zero to 47 to make 470, so 1 = brown So, 470 = yellow, violet, brown Now, find the 220W resistor.

  7. Check Resistance of Resistors R ~ 470W set multimeter to measure W

  8. Compute the Voltage Drops Across the Two Resistors (Hint: compute the total current provided by the power source and then apply Ohm’s Law to each resistor) 5V + - DV = 3.41V 220W 470W SOLUTION: DV = 1.59V Now, add the voltage rise of the power source (+5V) to the voltage drops across the resistors (negative numbers). 5V – 3.41V – 1.59V = 0

  9. Your Multimeter pincer clips – good for working with Boe-Bot wiring probes (push these onto probes) leads turn knob to what you would like to measure You will use the multimeter to understand and troubleshoot circuits, mostly measuring DC voltage, resistance and DC current.

  10. Use Multimeter to Measure Voltages Around Loop (1) From Vdd to Vss DV1 = _____ (2) Across the 470W resistor DV2 = _____ Remember . . . a RESISTOR is a voltage DROP and a POWER SOURCE is a voltage RISE DV1 - DV2 - DV3 = ________ (3) Across the 220W resistor DV3 = _____ Rises must balance drops!!!!

  11. Compare Measurements to Theory DV = 3.41V DV = 1.59V Pretty close!

  12. Kirchoff’s Voltage Law (KVL) Kirchoff’s Voltage Law says that the algebraic sum of voltages around any closed loop in a circuit is zero – we see that this is true for our circuit. It is also true for very complex circuits. DV = 3.41V 5V – 3.41V – 1.59V = 0 DV = 1.59V Notice that the 5V is DIVIDED between the two resistors, with the larger voltage drop occurring across the larger resistor.

  13. Gustav Kirchoff (1824 – 1887) was a German physicist who made fundamental contributions to the understanding of electrical circuits and to the science of emission spectroscopy. He showed that when elements were heated to incandescence, they produce a characteristic signature allowing them to be identified. He wrote the laws for closed electric circuits in 1845 when he was a 21 year-old student. Photo: Library of Congress

  14. Connecting an LED LED = Light Emitting Diode Diagram from the Parallax Robotics book Electricity can only flow one way through an LED (or any diode).

  15. Building an LED Circuit Vdd = LED These circuit diagrams are equivalent these holes are “connected” Vdd = 5V holes in this direction are not connected Diagram from the Parallax Robotics book

  16. Replace the 470W Resistor with the 10kW Resistor What happens and Why?? ANSWER: The smaller resistor (470W) provides less resistance to current than the larger resistor (10kW). Since more current passes through the smaller resistor, more current also passes through the LED making it brighter. What would happen if you forgot to put in a resistor? You would probably burn up your LED.

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