# Tag Info

56

You can't float everything without an isolation transformer - the neutral will be connected to ground at the entry into the building. For safety any class I equipment does need to remain grounded, in my lab I have an isolation transformer only for the equipment under test, the scope and power supplies still have the case grounds, and are tolerant of the ...

29

tl;dr because there are real-world issues that prevent us from setting I/O standards and other specifications willy-nilly. If EE were so simple a lot of us wouldn't have jobs or thesis projects. To start, there are tons of practical reasons why we don't just increase I/O voltage. It's not as simple as some guy crossing out 3.3v on a piece of paper and ...

23

Floating signals are usually not a good thing, but can be acceptable in some cases. In all those cases, the value of the signal does not matter. Not every signal is relevant all the time. A common example is the MISO line of a SPI bus. This is only actively driven when a slave device is selected (enabled). It's value is only relevant for a short time ...

13

Honest truth: What you're trying to do is easier implemented just by using a microcontroller with enough pins. It's probably even cheaper than an Attiny85. Who knows. But: If you really must, you can do various things to get more output out of a single line: Buy an IO expander that uses the 1-Wire (pseudo)standard, and implement a 1-Wire transmitter on the ...

12

Floating is a voltage term and, like any voltage, it must have a reference. That is: "Object A can be floating with respect to object B." If your shown circuit, both grounds are wired together, so the source, V1, is NOT floating with respect to the amplifier. However, if this was a battery operated widget, with no other connection, the whole thing is ...

11

What is the right way to float my home lab? If you want to make measurements that are isolated from ground, the only way to do this is with an isolation transformer if your scope is not isolated. There are very few reasons to do this, a high voltage setup would be one reason. Some AC measurements would be another. Differential probes are best. Do I ...

11

It has been solved already. Some microcontrollers have built in pull-up and/or pull-down resistors that can be enabled via software. But these are not active when microcontroller has no firmware so for safety reasons you might still want to have external resistors to keep stable state during powerup, reset or firmware download.

9

I believe... Leave Floating : Is meant for inputs. The pad is literally floating and is free to receive whatever noise is buzzing around your circuitry. Generally not a good idea for CMOS parts unless dictated by the part spec. Leave Open : Is for outputs. The pad on "Leave Open" is being driven by the pin if the pin is active. Which term you use for ...

9

Of course, I'm a nerd, so here's solutions less likely to be implemented by you, but worth mentioning for the fun of it: Shift Register based Shenanigans The following ideas are based on serial-to-parallel shift registers. Output Pin -> Data In You can just shift in your data to your shift register's serial data input. Problem: Shift registers need a ...

9

Logical reading (1 or 0) of a micro-controller may float at input GPIO pin if it is neither connecting to VCC nor GND, someone said it is because of surrounding RF interference. Yes, and static charge. When voltage affected by RF interference makes GPIO input pin voltage falls on undefined logical range (i.e. 0.8V - 2.2V for Raspberry PI) then it causes ...

8

I guess you are getting the doubt because of confusion that the moving part of the switch is opened and this is making you think that it is floating and so D2 must also be floating. No no no. The moving part of the switch and so D2 are at zero volts. D2 is input. And GND is zero volts. There is no current through R1. So no potential difference across R1. So ...

8

There is no right way to float your home lab. 1) No. Right way is not to float equipment that must be grounded. 2) No. Don't float any of them. Equipment that have grounded plugs NEED to be grounded for a reason. 3) No. Because again, equipment with ground pins need to be grounded! Having all lab equipment and the device being examined being connected to ...

8

Yes, you're fine with your approach. The EN pull up current is less than 2uA, so a 10K will allow you to remain below the threshold, and the microcontroller output will be able to pull it up to 5V (or at least greater than the threshold. Just stay below 7V on the enable pin and you'll be fine.) As you pointed out an open drain output on your micro doesn't ...

7

This is a typo. The not in the Note (as transistor points out) should not be there. Then it makes sense. Be sure to tie off any unused input, but unused outputs are fine. Line in TI article, Designing with Logic, Note: Unused outputs of a device should not be left unconnected (open). The title of the section where this line is referenced is: ...

7

You can have a lot of floating lines on your board during start-up of a microcontroller. Usually most of the pins of a microcontroller are initialized as input or even analog input, because the controller can't know how to configure its pins for the board it's placed upon. In this scenario most of the later outputs are floating at first, typically only a ...

7

If everything you do is DC, all you need is a DMM. Likely what you meant is that it is low voltage but DC to high frequency. Earth ground is advantageous two good reasons; 1) safety the line filter noise currents to the metal frame will go thru you if not earth grounded but your body has stray capacitance to earth line transients 2) performance EMI ...

7

As an ultra simplified, 1st year EE model, you can consider a disconnected input to a CMOS chip to be an RC circuit. The tiny gate leakage currents represent the R, and the tiny gate capacitances plus the stray capacitance from the pad or pin to the outside world being the C's. Change the external EM field to the outer plate of the capacitor enough (ground ...

6

The term "floating" refers to an input or tristated output that has nothing at all connected to it, so any tiny current can cause it to take on pretty much any voltage within limits. The input is solidly connected to +5 V when the switch is closed. When it is open it is connected to 0 V through R1. If the value of R1 is appropriate for the ...

6

One example comes to my mind: bus lines which are used by several ports at different times may be floating when there aren't any ports currently using them. I think the book made clear that you do not need them but they might just happen. The least thing that should be done in systems that have lines that may float (e.g. a data and address bus in a ...

6

The oscilloscope will show the voltage difference between the tip of the probe and the ground of the probe. Most scopes have 1 MΩ resistance between tip and ground, so the voltage you are measuring is affected the same as putting a 1 MΩ resistor between the two points you are connecting tip and ground to. For many circuits, 1 MΩ is high ...

6

It's my understanding that a load which has a SMPS can put noise back onto the power cord, which could reach another component that's plugged into the same outlet. Yes, that is true, but if the device conforms to current EMi legislation, this noise will be quite low. If it's a chinese $1 USB charger, maybe not. Never use a chinese$1 USB charger while in ...

6

You can use two comparators and the high-input-low values. For instance: simulate this circuit – Schematic created using CircuitLab The two comparators will give out a logic 1 when the voltage at the input is higher than 3/4 * Vcc (DATA one) or 1/4 * Vcc (EN one). When the attiny pin is pulled low, the voltage will be fixed to 0V; the comparators ...

6

Here is a schematic that will achieve the stated goal: simulate this circuit – Schematic created using CircuitLab When the GPIO is floating (i.e. micro-controller is off / booting) the transistor is turned on by R1 and EN is driven low. When the GPIO is asserted low by the microcontroller, it turns off the transistor, and EN is floated. Not necessary,...

6

There is very important rule in electronics: NEVER left anything out of control. So, if there is not strictly written in datasheet that the input has an internal pull-up or pull-down, DON'T let to have undefined state on this input. If you dont need this input, connect it to ground or Vcc, NEVER leave float. Such undefined states can cause some less or more ...

5

simulate this circuit – Schematic created using CircuitLab Figure 1. Redrawn circuit with negative rail at bottom. I'd say your circuit analysis is pretty good and your explanation of circuit use is a great help. Convention on circuit schematics is that current generally flows from top to bottom and since most of us reads left to right we generally ...

5

I would consider "Leave Open" and "Leave Floating" to both mean to not make any connection to the pin. The pin would normally be soldered to a pad on the PC board, but that pad would have no connection to other components.

5

A pin left open is not connected anywhere. Some pins, such as tristate output pins on logic chips, or MCU pins can be made to float by making them high impedance (programatically or via a control pin). They are still connected but have minimal effect on whatever they are connected to. Note that an open pin is just not connected so it's always high ...

5

simulate this circuit – Schematic created using CircuitLab Figure 1. A simple 3-state binary coding fed through a low-pass filter and monitored by two comparitors to extract the data. Note that many comparitors are open collector output and require a pull-up resistor. You will face some challenges getting the R1-C1 time-constant right.

5

You certainly do not want to float your equipment if you still have earthed stuff around you, or literally under your feet. That is especially true for (grounded) anti static mats and wristbands. That way lies an early grave.

4

To add to Barry's answer I'd also make these points: A floating driven power supply cannot send power through a path that does not directly connect its V+ and V- terminals, ... A chemical power supply, like most conventional batteries, cannot send power that doesn't connect its V+ and V- terminals, Within lumped circuit analysis, no device can deliver ...

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