1. EECS 373
On Operational Amplifiers and Other Means of Manipulating Voltage and Current

2. Once you’ve done your topic talk…
Send me your slides
Pdf is fine, but I’d prefer power point (and both is better yet).

3. Other Administrivia?
And yes, Merriam-Webster accepts that as an English word.

4. Analog—the bane of the computer engineer 
In embedded systems, you often need to deal with voltages and currents.
Often the outputs you have don’t match the inputs you need.
Generally the current or voltage is too small
Sometimes the voltage is too big.
Sometimes the values are in the wrong range.
Today we’ll touch on some ways of manipulating these values.
This is intended to give you some idea what options are out there
Often the details are tricky and/or annoying.
We expect you may need to ask for help…

5. Examples of where you might have problems.
You have 5V for power, but some devices need 3.3V for power.
You are using a device that generates too little current for your ADC, you may want to amplify the current but hold the voltage constant.
You may be using a UART or other serial bus where one device wants 3.3V or 1.7V and the other wants 5V.
You may be driving a motor that needs but you can only drive what do you do?

6. What are DC converters?
DC converters convert one DC voltage level to another.
Very commonly on PCBs
Often have USB or battery power
But might need 1.8V, 3.3V, 5V, 12V and -12V all on the same board.
On-PCB converters allow us to do that
Images from

7. DC converters
Probably the most common problem is dropping power from 5V to 3.3V.
Often because we’ve got a device that wants 3.3V as Vcc and everything else wants 5V.
The generic term for a device used to change voltages is “DC converter”
But when dropping it is sometimes called a “voltage regulator”.
Specific types are called “linear regulator”, “Low Dropout (LDO)”, and “Switching regulator”

8. Different types of DC converters
Linear converters
Switching converters
Simpler to design
Low-noise output for noise-sensitive applications
Can only drop voltage
And in fact must drop it by some minimum amount
The larger the voltage drop the less power efficient the converter is
(All voltage dropped is converted to heat).
Can be significantly more complex to design
**Don’t use for project**
Can drop voltage or increase voltage
“buck” and “boost” respectively
Generally very power efficient
75% to 98% is normal

9. Linear regulator
Input
Ground
Output

10. Linear regulators and capacitors
Specification for regulators almost always include required capacitors
If you don’t have them, your output may get noisy and cause all kinds of problems including reseting your chips.
Too big is better than too small.
May have required capacitor types (ceramic, etc.)
Be sure to check (most linear regulators don’t…)

11. Op-amps
We’ll briefly talk about using op-amps to do a few basic things.
Current buffering
Threshold detection
Etc.
I’m not going to talk much about single supply vs. dual supply.
is helpful though.

12. Very idealized basics

13. Voltage comparator Can change the ground input to any voltage.
Often just goes down to ground rather than –Vcc.

14. Voltage follower
How does this work?

15. And a bunch of others

16. Current to voltage and back.
Where would we have used a
current-to-voltage device?

17. Additional reading
Used for the last 4 slides.

18. N64 controller
Slides taken from a presentation by Aaron Ridenour, Ryan Wooster and Alex Jaeckel

19. Controller Inputs: A, B, L, R, Z, start, C-up C-down, C-left, C-right,
Inputs: A, B, L, R, Z, start, C-up C-down, C-left, C-right,
D-Pad(up, down, left, right), Joystick
Options: Rumble Pak, Memory Pak

20. Joystick
Two wheels positioned at right angles to each other, one for the x-axis, one for the y-axis.

21. OPEN Collector Pull-up resistor keeps the line high while idle.
To send 0, the output line is pulled low and connected to ground.
To send 1, nothing should be sent.
Do not drive the line high.

22. OPEN Collector 1 Sending a logical 0: 1

23. OPEN Collector Sending a logical 1: 1 1 1
Sending a logical 1: 1 1 1

24. Controller Encoding Each bit is sent in 4 𝜇𝑠 Logical 0:
Low for 3 𝜇𝑠, followed by high for 1 𝜇𝑠
Logical 1:
Low for 1 𝜇𝑠, followed by high for 3 𝜇𝑠

25. On a scope.
Pieter-Jan.com

26. Controller Encoding

27. Communication protocol
When a Command byte is sent to the controller, it sends a response depending on which command was sent.
Check Controller Command: 0x00
The controller responds with 3 bytes. The first two bytes are always 0x0500
Last byte is determined by:
0x01: If a controller pack is connected.
0x02: If no controller pack is connected.
0x04: If a previous command resulted in an error.

28. Communication protocol
Reset Controller Command: 0xFF
First resets the controller, including resetting the joystick calibration
Controller then responds as in the Check Controller Command

29. Communication protocol
Input Polling Command: 0x01
The controller responds with 4 bytes, encoding the button and joystick values
Byte
Data[7]
Data[6]
Data[5]
Data[4]
Data[3]
Data[2]
Data[1]
Data[0] 1 A B Z
Start
D-Up
D-Down
D-Left
D-Right 2
Joystick Reset L R
C-Up
C-Down
C-Left
C-Right 3
Signed joystick x-axis coordinate 4
Signed joystick y-axis coordinate
The joystick values range between -128 and 127, but the controller physically can only use from -81 to 81.

30. Example data waveform |----Command (console) 0x01-----|
start bit
stop bit A B Z St
reset L R
|----Command (console) 0x |
|----Data1 (controller) 0x00----|
|-----Data2 (controller) 0x00----|
stop bit
Joystick x-coordinate
Joystick y-coordinate
| Data3 (controller) 0x |
| Data4 (controller) 0x |
Images taken from:

31. Communication protocol
Controller Pack Read: 0x02
Used to read from the controller pack.
The command is followed by 2 bytes which indicate the address being read from and a CRC to verify the address.
The controller responds with 32 bytes of data from that address, followed by the data CRC.

32. References http://www.pieter-jan.com/node/10