# Tag Info

54

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 ...

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 ...

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 ...

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

In theory it is OK to connect them in parallel with two conditions: Each battery must be in a state where it can be voltage charged. This is fine for lead acid batteries unless they are very run down. Very discharged lead-acid batteries have to be charged with fixed current until they get to a minimum voltage, then they can be voltage charged. The power ...

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 ...

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 ...

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 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

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

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.

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.

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 ...

4

Float charging in parallel should work well enough as long as you charge them to this state separately, as you say you intend to do. This probably violates the most proper method of long term maintenance where a "topping charge" is occasionally applied to floated batteries BUT this is usually only once per 6 months so probably an issue. As ever with ...

4

All signal generators need a reference for the signal. Your old sig-gen likely had the output referenced to mains ground while your PC one may be floating. Assuming, that is, that whatever you are feeding is also referenced to the same ground. Reliance on the mains ground can be problematic though. Using the reference supplied from the signal generator is ...

3

There are a couple of ways that you can verify if the power supply is floating. 1) The easiest method involves using a piece of commercial test equipment called a "Hi Pot Tester". This is a device that provides a current-limited high-voltage (either AC or DC) across the device under test. You simply short both of the output DC terminals together and ...

3

One thing you haven't considered is that the particular 2N7000 sample you're experimenting with may be faulty (you could easily damage it with an ESD for example). Or perhaps you have got an STP55NE06 with a far better gate insulation than the spec requires, and an 2N7000 which just barely meets the spec. I suggest you repeat your experiments with a ...

3

short version: The assumption "What I want to know is, why does it seem like none of these limitations apply to the floating gate layer?" is incorrect, but with some caveats. You can make a floating gate on any process if you have your oxide clean enough. Your "grown oxide" between the channel and the first layer is much better because it doesn't have ...

3

A simple pull-down resistor (connection to GND via resitor) at the input can fix the problem. It would pull down the floating potential of the open line to 0V. Note: This works if the output impedance of the "voltage input" part (A) is low enough. It wouldn't be good if the "input voltage" part (A) is just a potentiometer because then the pull down ...

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