1. Gadget Lab Lecture 4: Powering your circuit… Components… Then it’s Project Time Dr. Cindy Harnett ECE Dept., U of Louisville Spring 2008

2. Powering your circuit Trend toward low power, low-voltage circuits… A few examples (with many exceptions!) 15V: stereo and other amplifiers 1970s-onward 12V-3V: 555 timer you used last week (some types) 5V: Transistor-transistor logic, USB 3.3V: wireless sensor networks 1.8V: “low voltage” computer memory (late 90s) 1.2 V: “ultra low voltage” memory. But people want an easy-to-find battery, usually one or more 1.5 V batteries.

3. Previously: Small DC Motor What can we do to drive the motor at 1.5V from a 6V battery? The voltage divider didn’t work because the motor’s resistance is too small. It shorts out R2. Also: voltage dividers are very “dissipative” --they draw a continuous current, wasting power.  Design new voltage divider based on the motor’s resistance…but note that the resistance changes over a cycle. Probably not a good approach.  Use a 1.5 V battery (but often need 6V elsewhere in the circuit)  Use a 1.5 V voltage regulator - a specialized chip that takes 6v and outputs 1.5V -- this could work OK and save power.  Use “pulse width modulation” -Drive the motor with a pulsed 6V signal that averages out to 1.5 V over time. A very common solution.  Use the voltage regulator with a “buffer chip” that does not pull down the output voltage (An op-amp or transistor).

4. Look at voltage regulators 78L05 78L05 regulator Turn 9V into 5V with very little lost power 5V output doesn’t change if load changes 9V5V TO-92 styleTO-220 style

5. What about getting a high voltage from a low voltage battery? One method: the “boost converter” Voltage across an inductor depends on the rate of change of current: V=L di/dt A switched signal induces a large voltage across the inductor. Use diodes to control the direction of current, and a capacitor to store the high voltage. The EL driver project uses this strategy to produce a 150V, 200 Hz AC signal from 3V DC. Small inductors Diodes

6. High voltage from low voltage Commercially available DC HV converters: 100 to 10000V DC from 5- 12 V DC Drives MEMS actuators, piezoelectric devices, photomultiplier tubes, electrophoresis chips. Small current (Power is conserved: P=IV) Looking inside, there is a small inductor and some other components.

7. Component identification Some websites help you learn to identify ICs and other components (links on BlackBoard) Good for identifying a “mystery component” from a salvaged board or a junk drawer. Teardowns- new insights?? http://www.uchobby.com /index.php/2007/07/15/id entifying-electronic- components/

8. Component Quiz

9. Projects Work on the project of your choice Using solderless breadboard first, then soldering if possible, is a good idea. “Troubleshooting” tips: 1.Use resistance meter to check all pins are really connected how you want 2.Compare to a known-good circuit. 3.Most parts are symmetrical, but sometimes polarity is important. Is it plugged in backwards/upside down/not at all?