Here are some of the learning experiences, ideas, and knowledge I gained while revisiting analog and digital circuits. Let’s share and learn together!
1. HC is a CMOS level, while HCT is a TTL level.
2. LS input is open to a high level, but HC input should not be left floating. For HC, an external pull-down resistor is typically required to ensure a defined state when the input is inactive. LS does not require this.
3. LS output has a strong pull-down and weak pull-up, whereas HC has balanced pull-up and pull-down characteristics.
4. The operating voltage for LS is limited to 5V, while HC can operate between 2V and 6V.
5. CMOS can drive TTL, but the reverse is not possible. When driving a CMOS circuit with a TTL one, a pull-up resistor must be added to raise the voltage between 2.4V and 3.6V so that the CMOS can detect a high level.
6. The driving capability differs: LS has a maximum high-level drive of 5mA and a low-level drive of 20mA, while CMOS provides around 5mA for both high and low levels.
7. RS232 uses +12V for logic low and -12V for logic high.
8. The 74 series is for commercial use, while the 54 series is for military-grade applications.
9. TTL high level is >2.4V, and low level is <0.4V, with a noise margin of 0.4V.
10. OC (open collector) and OD (open drain) gates require an external pull-up resistor to function properly. These gates can only sink current, so the pull-up resistor and power supply must provide current. They are often used for driving large loads or as level shifters.
11. If the input current of a CMOS chip exceeds 1mA, it may get damaged.
12. When using long signal transmission lines, a matching resistor should be placed at the CMOS circuit end.
13. Adding a 10kΩ resistor in series with the input of a gate can cause the input to read as high instead of low.
14. To connect a 3.3V CMOS circuit (like a microcontroller) to a 5V CMOS circuit (like 74HC), you can replace 74HC with 74HCT, use a voltage converter, or set the MCU’s I/O to open-drain and add a pull-up resistor to 5V.
15. Logic gates have different behaviors: high-level output is sourcing current, and low-level output is sinking current.
16. Open-drain circuits require an external pull-up resistor. The pull-up voltage determines the output level. This allows for level shifting between different voltage domains. However, the rising edge may be slow, so it's better to rely on the falling edge.
17. Several level conversion methods include:
(1) Transistor + pull-up resistor method
(2) OC/OD device + pull-up resistor
(3) Using 74xHCT series chips for 3.3V → 5V conversion
(4) Over-limit input step-down method
(5) Dedicated level shifter ICs like 74LVC164245
(6) Resistor divider method
(7) Current limiting resistor method
18. Non-polar capacitors (e.g., 0805, 0603) vs. polar capacitors (e.g., aluminum electrolytic, tantalum).
19. Common IC package types: PQFP, BGA, PGA, PLCC, SOP, TOSP, SOIC.
20. QFP has gull-wing leads, BGA has ball grid arrays, PLCC has internal hook legs, SOJ has internal hook feet, and SOIC has gull-wing leads.
21. Shielded cables suppress static electricity, while twisted pairs reduce electromagnetic interference.
22. Analog signal sampling techniques include differential amplifiers, shielded cables, and current-mode signals with RC filtering.
23. Unused IC pins should not be left floating. Unused op-amps should be connected as voltage followers, and unused microcontroller I/Os should be configured as outputs. Multiple power and ground pins must all be connected.
24. Resistor color codes: 4 bands for standard resistors, 5 bands for precision.
25. Resistors serve various purposes: current limiting, voltage division, biasing, filtering, and impedance matching.
26. Capacitors are used for DC blocking, bypassing, coupling, filtering, compensation, charging/discharging, and energy storage.
27. Capacitance values are usually in pF for small capacitors and uF for electrolytic ones.
28. Key capacitor parameters: capacitance, voltage rating, and maximum operating temperature.
29. Inductors are used for filtering, oscillation, and magnetic energy storage.
30. Inductor types: air-core and core-based (including iron-core and copper-core).
31. Diode classification includes material (silicon, germanium) and purpose (rectifier, Zener, LED, photodiode, varactor).
32. FETs are voltage-controlled, while BJTs are current-controlled. Choose FETs for low-current sources and BJTs for low-voltage, high-current applications.
33. Sockets are rectangular connectors, while slots are rectangular grooves.
34. Testing a crystal oscillator with a multimeter RX10K range: normal value is infinite; if it shows resistance or zero, the crystal is faulty.
35. When an IO port outputs a high level, it sources current; when it outputs a low level, it sinks current.
36. Driving inductive loads requires a current-limiting resistor or a flyback diode.
37. 9013 transistor provides up to 300mA of drive current.
38. Output data should be latched, and input data should use three-state buffers to avoid bus conflicts.
39. 8-bit parallel output ports (e.g., 74LS377, 74LS273) require latching; 8-bit parallel input ports (e.g., 74LS373, 74LS244) need three-state buffers.
40. Serial-to-parallel interfaces: 74LS165 for input, 74LS164 for output.
41. Keyboard interface methods: program scan, timing scan, interrupt mode, and dual-function key design.
42. For TTL loads, focus on DC characteristics due to high current and low capacitance; for MOS loads, focus on AC characteristics due to low current and high capacitance.
43. Pay attention to bus load balancing to prevent signal distortion.
44. Pull-up resistors improve signal levels, enhance EMI immunity, suppress static interference, and reduce reflected wave interference.
45. Two-stage voltage regulators are more stable for voltage regulation.
46. Transmission line impedance matching: terminal parallel, series, DC blocking, and clamp diode methods.
47. Grounding types: housing grounding (true ground) and working grounding (floating ground).
48. MCU grounding: digital, analog, power, signal, AC, and shielded grounds.
49. One-point grounding for low-frequency (<1MHz), multi-point grounding for high-frequency (>10MHz).
50. Avoid sharing ground and signal ground; separate digital and analog grounds and connect them at one point.
51. High-frequency bypass capacitors are small (e.g., 0.1uF), decoupling capacitors are large (10uF+).
52. Diode applications: limiting, clamping, switching, rectifying, and low-voltage regulation.
53. Bypass capacitors are small (0.1uF, 0.01uF), while decoupling capacitors are larger (10uF+).
54. Pull-up resistor usage: for TTL-to-CMOS conversion, OC gates, improving drive strength, preventing static damage, increasing noise margin, reducing EMI, and suppressing reflections.
55. From power-saving and sinking considerations, larger resistors are better; from drive current, smaller resistors are better.
56. Pull-up clamps an undefined signal to a high level and limits current flow.
57. Bypass capacitors shunt AC noise, while decoupling capacitors provide local power and reduce noise propagation.
58. Active buzzers have built-in oscillators and work with power, while passive buzzers require a square wave signal (2kHz–5kHz) to activate.
The Fume INFINITY is our newest 3500 puff disposables vape that's big enough to offer tremendous value, hot sale now.we are professional manufacturer ,contact with us get best price.
Fume 3500 Puffs Disposable Vape ,Fume 3500 Vape Pen,Fume 3500 Disposable Vape Device,Fume 3500 E-cigarette,Wholesale Fume 3500Disposable
Shenzhen Ousida Technology Co., Ltd , https://en.osdvape.com