Electronics notes / Inputs and outputs

⚠ This is for beginners and very much by a beginner / hobbyist It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book. Some basics and reference: Volts, amps, energy, power · batteries · wallwarts and power bricks · resistors · transistors · fuses · diodes · capacitors · inductors and transformers · ground Slightly less basic: amplifier notes · varistors · changing voltage · baluns · frequency generation · Transmission lines · skin effect And some more applied stuff: IO: Input and output pins · wired local IO · wired local-ish IO · ·  Various wireless · 802.11 (WiFi) · cell phone Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions Audio and video notes: See avnotes Platform specific: : Microcontroller and computer platforms ·· Arduino and AVR notes · ESP series notes · STM32 series notes · Teensy series notes · RP2040 and RP2350 notes Less sorted: USB notes · Ground · device voltage and impedance (+ audio-specific) · electricity and humans · Soldering · landline phones · pulse modulation · PLL · multimeter notes · signal reflection · Project boxes · resource metering · Radio and SDR · vacuum tubes · Unsorted stuff · 'E-fuse' Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer · See also Category:Electronics.

High side versus low side switching / driving / sensing

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Transistor output stages

Open-drain / open-collector

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

On ADCs and DACs

ADC

An Analog-Digital Converter (ADC) takes a voltage signal, and turns it into numbers to be consumed digitally.

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.

Impedance and buffering

ADC operation works with current, so they have relatively low-impedance inputs. As such, they may interact with the source circuit (consider e.g. SAR ADCs, which are also a non-linear load on the source circuit).

Impedance also easily varies with (sampling) frequency. This seems particularly true of high-performance ADCs.

If you want to minimize the interaction with the circuit you can use a buffer, such as an op amp, which presents a high-impedance load to your circuit and a lowish-impedance output to the ADC. (Assuming you were not already using an op amp construction (e.g an instrumentation amp) anyway, you can e.g. make it a fairly-simple voltage-following unity-gain amp)

Some typology

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

You may only care about a few of these terms, but they'll be useful.

Input structure

• Single-Ended

measures the difference between one pin and ground

• (Fully-)Differential

measures the difference between two pins (i.e. no ground)

Floating-differential and pseudo-Differential relate to voltage ranges and noise (verify)

Getting the value

Resolution and speed depends entirely on application. Imaging and such needs to be both, movement needs speed more than accuracy, while temperature and such can be slow if that means it's more accurate, or just cheaper.

• Ramp Counter (a.k.a. digital ramp)

https://www.analog.com/media/en/training-seminars/tutorials/MT-026.pdf

• Delta-sigma - refers to a way of dealing with noise, used by both ADCs and DACs

medium speed, high resolution

https://en.wikipedia.org/wiki/Delta-sigma_modulation

http://www.ti.com/lit/an/slyt423/slyt423.pdf

http://www.allaboutcircuits.com/vol_4/chpt_13/9.html

• Single-slope

• Dual-slope

slow speed, good resolution

• Successive Approximation Register (SAR)

medium speed, high res

most common, because of the above and low cost

• Flash

high speed, medium resolution

https://en.wikipedia.org/wiki/Flash_ADC

• Pipelined

effectively multiple flash type, better resolution

See also:

• http://www.maximintegrated.com/app-notes/index.mvp/id/1108
• http://www.hardwaresecrets.com/printpage/How-Analog-to-Digital-Converter-ADC-Works/317

DAC

A Digital-Analog Converter (DAC) takes numbers and turn them into voltages.

What do DACs speak

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

That varies.

It's often one of

• I2C or SPI

a little more fiddly to use for sound because the timing is either separately set, or not really defined (so not strictly regular)

but perfectly good for "set voltage level on output"

• I2S - good at sound

note that there are technically some dialects

• something specific
  • e.g. OPL style FM (e.g. YM3812, YMF262) want a specific style of DAC (e.g. YAC512), which sends floating-point-like values
  • TI DSPs often speak speak TI's McBSP, and so various of their ADC/DACs

Consider also:

• Pulse Density Modulation in general

• Abusing a serial port at a high rate, see e.g. Mozzi's PDM_VIA_SERIAL

imperfect, but the serial hardware does the timing

• Mozzi's PDM_VIA_I2S

On the cheap: Resistor ladder

Basic idea: If you can change many digital pins at exactly the same time (e.g. often 8 on many microcontrollers, or a classic parallel port), then putting a resistor ladder on it means each contributes a different voltage level.

Laid out in R-2R a.k.a. R2R style (there are other configurations), you can can make 2^amt equal voltage levels (256 for 8 pins), in a way that makes 256 equally spaced levels.

This is a crude 8-bit DAC.

E.g. the Covox Speech Thing was basically just a bunch of resistors on a parallel port, the Disney Sound Source a data-buffered variant.

Especially the speech thing was 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 bits of concurrent output is rare in this approach, in part because digital output channels are oftencontrollable 8 at a time

may be acceptable at lower frequencies, but faster is harder to get right

Example:

• http://www.radanpro.com/Radan2400/mikrokontroleri/Jesper%27s%20AVR%20pages%20-%20MiniDDS.htm

• https://en.wikipedia.org/wiki/Covox_Speech_Thing

On the cheap (if your IC happens to have it): Oversampling fast PWM

So, PWM at the signal rate is poor.

But what if we can PWM much faster than the signal's rate, and lowpass the result to the signal's rate? After the lowpass you're looking at something is mostly its average.

Oversampling PWM makes its output more linear and reduces some noise sources (lessening requirement to any filtering), and preferably we want two orders of magnitude faster, order of ~1MHz for a 20kHz signal.

That speed basically requires dedicated PWM circuitry in the IC.

Limitations:

• if you don't have very fast PWM, the net result is high noise

• the lowpass is probably 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 impossible for audio rate, particularly if you also want to do anything else in the microcontroller

• even if the PWM output is regular due to dedicated hardware, we also need to update the sample to put out with strict regularity

this is what interrupts are good at. It just occupies the CPU.

you'ld really prefer a small buffer, so that you don't need interrupts to be at at audio rate (if it is, expect everything else to be secondary to this). At this point, you're starting to describe a dedicated DAC

• multiple channels may be possible, but how easy this is varies with IC

this might actually help you e.g. produce different types of wave at the same rate

Example:

• https://web.archive.org/web/20230930221045/https://home.csulb.edu/~hill/ee470/Lab%202d%20-%20Sine_Wave_Generator.pdf

• Raspberry Pi's onboard sound is actually dedicated PWM pins, at 50MHz(verify), plus a filter and buffer (exact details vary)

Some simple ADCs and DACs for DIY

See Some simple ADCs and DACs

CODECs

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

A codec (short for coder/decoder[1]) is mostly just an ADC + DAC with some shared hardware.

This can be cheaper, smaller, fewer wires, yet functionally be much like separate parts.

The two are often synchronized, i.e. sharing the same clock, which can help reduce drift issues and latency between them, but that also depends on further details (and whether you care about this at all also varies).

It may sometimes mean a little less work to manage both, but this gets into engineering choices, and there are no hard conclusions about what it means to the end user.

Most codecs are designed for audio uses, because there aren't a lot of signal uses that need this.

oversampling / supersampling

See Oversampling

See also

Digital sample capture, storage, reproduction