23 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....
Olin Lathrop's user avatar
21 votes
Accepted

Why doesn't this circuit work?

The cathode of the LED must be connected to the ground not Vcc
Paul Ghobril's user avatar
  • 2,906
19 votes

How to read input from multiple (dozens) of sensors, with fewer pins

Dozens of temperature/humidity sensors sounds like a set of greenhouses, eventually with servos to open windows or run pumps ... If you have dozens of anything, modularity and testability are really ...
jonathanjo's user avatar
  • 13.9k
14 votes
Accepted

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 ...
mguima's user avatar
  • 1,435
13 votes
Accepted

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 (...
Theodore's user avatar
  • 2,121
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 ...
Harry Svensson's user avatar
11 votes
Accepted

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#).
MarkU's user avatar
  • 14.6k
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 ...
StarCat's user avatar
  • 1,134
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.
Rodo's user avatar
  • 1,054
9 votes
Accepted

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)...
jonk's user avatar
  • 77.8k
9 votes
Accepted

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 ...
brhans's user avatar
  • 14.7k
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 ...
Harper - Reinstate Monica's user avatar
9 votes
Accepted

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,...
LorenzoDonati4Ukraine-OnStrike's user avatar
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 ...
Olin Lathrop's user avatar
8 votes
Accepted

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 ...
CL.'s user avatar
  • 19.2k
8 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 ...
Dave Tweed's user avatar
  • 172k
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 ...
ratchet freak's user avatar
8 votes
Accepted

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 ...
Neil_UK's user avatar
  • 165k
8 votes
Accepted

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.
Eugene Sh.'s user avatar
8 votes

Steer multiple LEDs with one microcontroller pin

Addressable RGB LED strips work with one single data pin.
Justme's user avatar
  • 143k
7 votes
Accepted

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 ...
Spehro Pefhany's user avatar
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 ...
skrrgwasme's user avatar
7 votes
Accepted

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. ...
scary_jeff's user avatar
  • 1,987
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 ...
David A.'s user avatar
7 votes

Can rotary encoders be multiplexed?

Yes, but... Yes, they can, it is simply a question about the sample rate. You have to perform some calculations. You have to determine the maximum speed for which you want your encoders to function. ...
pipe's user avatar
  • 14k
7 votes
Accepted

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 ...
Billy Kalfus's user avatar
  • 1,021
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 ...
Bimpelrekkie's user avatar
  • 80.7k
7 votes
Accepted

Clipping when using a CD4051 analog multiplexer

It will work okay, in fact series resistance will be near minimum, but leakage will be relatively high (perhaps in the few uA range) increase at high junction temperature (perhaps >100uA at Tj=100°...
Spehro Pefhany's user avatar
7 votes
Accepted

Using 1N4148 diodes on segments of multiplexed 7-segment LED display

You are correct in looking for the design decisions, and all the information you need is on hand. From your schematic and an assumption that the segment currents are in the 25 mA range we can work out ...
Jack Creasey's user avatar
  • 21.7k
7 votes

Why don't analog multiplexers specify PSRR?

I don't think you could give an accurate PSRR without defining external circuitry, because the impedances of the circuit on both sides of the switch determine the effective rate. Instead, you get the ...
W5VO's user avatar
  • 18.6k

Only top scored, non community-wiki answers of a minimum length are eligible