1. A lecture for Arduino Course, Winter 2017/18
A few useful circuits
Boris van Sosin,
Commissar-Engineer
A lecture for Arduino Course, Winter 2017/18
Technion, IIT

2. Voltage Divider
𝐼= 𝑉 𝑅
Ohm’s Law:
𝐼= 𝑉 𝑅
𝐶𝑢𝑟𝑟𝑒𝑛𝑡= 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒

3. Voltage Divider Assume: When open: Voltage reader has R=∞ to ground
𝐼= 𝑉 𝑅
Assume:
Voltage reader has R=∞ to ground
When open:
V read = 0V
𝑉=0𝑉
𝐼=0
𝑉= 𝑉 𝐺𝑁𝐷 =0𝑉

4. Voltage Divider Assume: When closed: Voltage reader has R=∞ to ground
𝐼= 𝑉 𝑅
Assume:
Voltage reader has R=∞ to ground
When closed:
V read = 5V
𝑉=5𝑉
𝐼= 𝑉𝐶𝐶 𝑅1
𝑉= 𝑉 𝐺𝑁𝐷 =0𝑉

5. Generalized Voltage Divider
𝐼= 𝑉 𝑅
Total current: 𝐼= 𝑉𝐶𝐶 𝑅1+𝑅2
Equal to current over each resistor 𝐼= 𝐼 𝑂𝑣𝑒𝑟 𝑅2
Therefore:
𝑉 𝑂𝑣𝑒𝑟 𝑅2 = 𝐼 𝑂𝑣𝑒𝑟 𝑅2 ⋅ 𝑅 2 =𝑉𝐶𝐶⋅ 𝑅 2 𝑅 1 + 𝑅 2
𝐼= 𝑉𝐶𝐶 𝑅1+𝑅2
𝑉= 𝑉 𝐺𝑁𝐷 =0𝑉
𝑉 𝑂𝑣𝑒𝑟 𝑅2 =𝑉𝐶𝐶⋅ 𝑅 2 𝑅 1 + 𝑅 2

6. Voltage Divider
Uses:
Lots of Arduino inputs

7. Low-Pass Filter Charging a capacitor through a resistor
Initially capacitor is empty
𝑉 𝑟𝑒𝑎𝑑 =0𝑉
As capacitor charges, 𝑉 𝑟𝑒𝑎𝑑 rises

8. Low-Pass Filter Charging a capacitor through a resistor
RC Law: 𝑉 𝑡 = 𝑉 𝑚𝑎𝑥 ⋅ 1− 𝑒 −𝑡⋅𝐶𝑜𝑛𝑠𝑡 𝑉 𝑡
Chart by desmos.com

9. Low-Pass Filter Charging a capacitor through a resistor RC Law
RC Constant depends on resistor and capacitor
𝑉 𝑡 = 𝑉 𝑚𝑎𝑥 ⋅ 1− 𝑒 − 𝑡 𝑅⋅𝐶
Greater resistance and/or capacitance means slower charge

10. Low-Pass Filter
Uses:
Smoothing a signal

11. Low-Pass Filter Uses: Smoothing a signal
Smoothing digital waveform to (nearly) analog
Smoothing high frequency analog
Noise filtering

12. H-Bridge Recall first tutorial: Powering a DC motor:
Reversing a motor:

13. H-Bridge
Control direction via logic?
Simplified solution: Switches

14. H-Bridge Control direction via logic
Close diagonal pair of switches to power motor
Close other pair to reverse

15. H-Bridge Control direction via logic Problem: illegal states
Short circuit!

16. H-Bridge Connecting to logic: Replace switches with transistors
HIGH (or PWM) to D5
HIGH (or PWM) to D6 for reverse direction
NEVER POWER BOTH!
What is missing?

17. H-Bridge Connecting to logic
Diodes, capacitor, protection against illegal state

18. H-Bridge Can be contained in a chip L293D 4x Half H-Bridge
L298 2x Full H-Bridge

19. Increasing No. of Outputs
Arduino UNO has 20 I/O pins
TX/RX
12 digital I/O
6 digital Out + Analog In
How can this be increased?

20. Shift Register Shift register
Recall from Digital Systems / Logic Design
Convert Serial to parallel

21. Shift Register Shift register
Demo: Write 1100 to a 4-bit shift register
Strategy: Write in reverse order

22. Shift Register
Shift register
Write 0 ? ? ?

23. Shift Register
Shift register
Write another 0 ? ?

24. Shift Register 1 1
Shift register
Write 1 ?

25. Shift Register 1 1
Shift register
Write another 1 1

26. Shift Register Problem: look at previous state Current output is 100
Is it valid? ?

27. Shift Register Problem: Intermediate output states
Solution: second layer of registers
Requires “Latch out” control