24 votes

How can 16 buttons be connected with only 8 wires?

How can this work without any multiplexer? It doesn't. The keypad board seems to have just switches, with maybe some diodes we can't see. However, the left board looks like it has a processor on it....
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21 votes
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Why doesn't this circuit work?

The cathode of the LED must be connected to the ground not Vcc
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  • 2,577
14 votes

Reading hundreds of inputs with a single atmega32

Break the buttons into rows and columns, like is done with a keyboard. 12x12 will give 144 possible buttons, so should work. Then you'll need to use encoders to translate those lines into binary. 3 ...
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14 votes
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How can I control 8 LEDs using only 5 pins of a microcontroller?

8 leds on/off have 2^8 = 256 possible states 5 control pins on/off have 2^5 = 32 possible states Since 32 < 256, and you can't use shift registers or i/o expanders, it would be impossible... But if ...
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  • 1,375
13 votes
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Control one relay via multiple 12 V DC signals

Since you need isolation, you will need a relay for each appliance. Even if you didn't strictly need the isolation, it would be recommended since it might be hard to safely share the same voltage (...
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  • 1,664
12 votes
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What's the maximum number of outputs you can control from a microcontroller with n outputs?

It depends on what you mean by "control". Are you confining yourself to simple combinatorial logic, or are serial protocols allowed? In theory, you could control an arbitrary number of outputs from a ...
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  • 165k
11 votes

Reading a huge number of analog sensors in real time

The obvious answer is muxing, this means that you make electric path's dynamically. So just iterate through the whole matrix, one at a time, or as many ADC (Analog to Digital Converter) inputs as you ...
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11 votes
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What does INH as an IC pin label mean?

They are representing that signal as active-high Inhibit (INH), which is logically equivalent to active-low Enable (EN#).
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  • 13.4k
10 votes

How can I control 8 LEDs using only 5 pins of a microcontroller?

Use addressable LEDs like WS2812B or similar. You’d need only 1 pin (plus power and ground) to control hundreds of them. They are available individually or as part of an LED strip (which can usually ...
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  • 1,009
10 votes

Steer multiple LEDs with one microcontroller pin

Upgrade you MCU to one with more pins. It will be cheaper than adding more parts.
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  • 488
9 votes

How to measure trace impedance?

There is no* way to measure trace impedance with a simple multimeter. Measuring trace impedance requires, at minimum, an oscilloscope and an impulse generator of some sort. Here's an article about ...
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9 votes
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What is the purpose of diodes in flip-dot displays?

If we redraw your circuit without the diodes, we have this: simulate this circuit – Schematic created using CircuitLab Now imagine you drive Column-1 High and Row-1 Low (and Column-2 and Row-2 ...
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  • 13.3k
9 votes

How can 16 buttons be connected with only 8 wires?

Without diodes... you'll get phantom rectangles. For instance in your example (2,2) (2,3), (3,2), and (3,3); you chose an ironic example by choosing a rectangle. If you actually press all four, it ...
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9 votes
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What is the difference between an analogue multiplexer and digital multiplexer?

The operation of any multiplexer (MUX for short) is conceptually the same, be it analog or digital. In essence you have a set of numbered data inputs (usually a power of 2, say \$N=2^n\$ inputs named,...
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8 votes
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What are the "No Connect" terminals on this multiplexer and what purpose do they serve?

No connect means just that -- don't connect the terminal to anything. They often appear on devices because the manufacturer uses a standard form factor that has more terminals than are needed for ...
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  • 571
8 votes

Making an ID of a board type

You say a micro in the base unit needs to identify the board type, and that these plugin boards already have a IIC bus going to them. This is a no-brainer. Put some device the micro can detect on ...
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8 votes
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How do you implement the following function using nothing but 2:1 MUX?

It's not too complex, I think, assuming you worked out the equation you wanted correctly (I'll assume you did okay there.) Start by looking at the equation for a 2-in MUX: $$ \begin{align*} M_2(A,B,S)...
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  • 70.2k
8 votes
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Analog Mux as Cheap I2C Mux?

Analog multiplexers work just fine for I²C signals (if you keep the impedance and parasitic cpacitance small enough, which is usually not a problem). I²C multiplexers are more complex because they ...
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  • 14.5k
8 votes

What is this kind of "Multiplexer" called?

A digital encoder or Priority Encoder. They will often have \$2^n\$ inputs and \$n\$ outputs. Additionally there will be an any-active output and an enable input. You can combine multiple encoders ...
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8 votes
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Is space division multiplexing really multiplexing?

Space Division Multiplexing sounds like snake-oil, but it's worth treating it as a topic for study, as there are costs and benefits when applying it. It's defined as pushing several independent ...
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  • 141k
8 votes
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What does this schematic mean?

This notation means a bus line with the width noted by the number written next to it. In your case it is 2-bit wide bus. It is used to make the drawing less convoluted by reducing lines drawn.
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  • 9,612
8 votes

Steer multiple LEDs with one microcontroller pin

Addressable RGB LED strips work with one single data pin.
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  • 89.2k
7 votes
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Reading and processing 32+ ADC channels at high frequencies

100Hz on 32Channels sounds very perfectly doable. Presuming we are talking 8 to 12 bits, that's only 12 * 32 * 100 = 38400 bits per second of sampling work. Even 16bit or 32bit per channel wouldn't ...
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  • 18k
7 votes
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What is Vee on a 74hc4051 mux?

The 74HC4051 has level shifters inside that allow you to use a logic supply that is GND to Vcc and another supply voltage Vee that is less than (or equal to) GND. This is a great advantage when you ...
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7 votes

What does a 'full 18×16 barrel shifter' mean?

I also found it hard to find a concise description of this notation. However, by plugging in some different values for n and k in Google searches for "n x k barrel shifter", I was able to find this ...
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7 votes
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Why isn't this decoder being inferred as a LUT?

The RTL schematic shows you how it has interpreted your code. As you can see, it has the exact combination of AND gates and multiplexers that your code describes. ...
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  • 1,937
7 votes

Difference between i2c switch and i2c mux

The two chips are NOT the same: The TCA9544A is an I2C Mux. An I2C Mux multiplexes any one of N downstream ports to the upstream port (1 to 1). The TCA9546A is an I2C Switch. An I2C Switch ...
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7 votes
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Reading a huge number of analog sensors in real time

Depending on your price range, you may want to consider using an FPGA between your Raspberry Pi and ADCs, such as the DE0-Nano Board, which has good support as an introductory FPGA dev board. This ...
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  • 1,011
7 votes
Accepted

Not enough pins, looking for a "demultiplexer" that keeps state

What you are looking for is a GPIO "expander" chip. There are many available, typically using I2C or SPI to connect to the microcontroller. The Microchip MCP23017(I2C)/MCP23S17(SPI) is just one ...
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  • 165k
7 votes

Control one relay via multiple 12 V DC signals

When any appliance reaches a specified temperature, it sends out a continuous 12 VDC signal. This is intended to activate a relay to run a ventilation fan. Then those 12 V signals are powerful enough ...
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  • 78.8k

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