Electronics notes / Inputs and outputs
Contents
High side versus low side switching / driving / sensing
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Some limits and choices
High versus low side sensing
Buffers
Transistor output stages
Open-drain / open-collector
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Common collector / Common drain
Totem-pole, push-pull
Other details
Transient voltage and ESD protection, snubbers
Protection diodes (inputs and output pins)
TVS diodes
Snapback
RC and RCD snubbers
Crowbars
Gas Discharge Tubes
MOVs
Trisil
Unsorted
See also (transients)
On ADCs and DACs
ADC
An Analog-Digital Converter (ADC) takes a voltage signal and turns it into numbers to be digitally consumed.
Well, most ADCs do voltage sensing. A few have extra circuitry to be current-input ADCs (which mostly just means a resistor setup, but probably better specced than you can easily make), many of them for specific applications.
On quantization
Fluctuating readings
DAC
Multiplying DAC (type)
Upsampling DACs
On the cheap: Resistor ladder
Basic idea: If you can change many (e.g. often 8 on microcontrollers) digital pins at the same time, then putting a resistor ladder on them means each contributes a different voltage level, and you can make 2amt voltage levels (256 for 8 pins).
E.g. the Covox Speech Thing was basically just a bunch of resistors on a parallel port. adopted by some games and music trackers.
Limitations:
- you still need to write out new data with strict regularity
- which is what interrupts are good at, but this will occupy a bunch of CPU power
- The Disney Sound Source solved this by being buffered (but fixed the output rate to a relatively poor 7kHz)
- the resistors' voltage contribution won't be perfect to contribute exactly what they should.
- making equal steps (to produce undistorted signals) takes either precision resistors or a bunch of measuring and matching beforehand.
- the more bits you have, the harder it gets - 8 is quite doable, but it starts getting impractical around 12 bits
- more than 8 bit is rare
- it's often the max you can change at the same time (single uC port)
- using multiple ports is hard to get quite right, though may be acceptable at lower frequencies
Example:
On the cheap: Fast PWM
Basic idea: If we can PWM much faster than audible (by preferably two orders of magnitude - which basically "if we have a dedicated PWM circuit in the IC"), then the duty cycle is controlled precisely enough that putting it through a lowpass means the result is stable enough (being an average of that duty cycle).
These work fine, though are limited frequency-wise. They're can work pretty decently in audible frequencies.
Limitations:
- the lowpass is fixed
- so it has a range where it works best, which is part of your design
- which is why this can't be a more general-purpose DDS
- without dedicated PWM circuitry the timing issues would make this a horribly task, particularly if you also want to do other things in the microcontroller
- even then we need to update the PWM with strict regularity
- this is what interrupts are good at. It just occupies the CPU.
- i.e. even when it's not CPU-intensive it's still timing-critical
- Expect everything else to be secondary to this.
- multiple channels may be possible (varies with IC) but may have to be related
- which is perfectly fine if you e.g. wanted different types of wave at the same rate
Example:
- http://digital-wizard.net/mcu_interfacing/sine_wave_generation
- https://web.csulb.edu/~hill/ee470/Lab%202d%20-%20Sine_Wave_Generator.pdf
- Raspberry Pi's onboard sound is actually PWM pins, plus a filter and buffer (exact details vary)
