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Low voltage but no ground [message #156286] Mon, 14 July 2014 09:31 Go to next message
messages@element14.co
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I am curious about ICs, I want certain pins to remain at low voltage/Low value/Zero value, that is if they were hooked to the ground, can I leave them unconnected or do they have to be connected to the ground anyway? Kind RegardsOriginal article at http://www.element14.com/community/message/120244?tstart=0#120244.

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Re: Low voltage but no ground [message #156360 is a reply to message #156286] Tue, 15 July 2014 23:31 Go to previous messageGo to next message
messages@element14.co
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If you want a pin to equal zero AKA go low you have to use ground. You can configure a circuit to momentarily make the pin low or another to have high or low settings using two different types of switches. With either switch the circuit is the same, to build it you need a 10 thousand ohm resistor, a switch and some wire. Start by connecting one wire to one pin of the switch to the 10k resistor and the other side of the resistor to your positive voltage supply next connect the same pin that the resistor is connected to on your switch to your IC pin that you want low or high and finally connect the other pin of the switch to ground. Now that your circuit is complete when you activate the switch the IC pin will ground and when the switch is deactivated the pin will be high.Have a nice day and happy buildingOriginal article at http://www.element14.com/community/message/120560?tstart=0#120560.

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Re: Low voltage but no ground [message #156361 is a reply to message #156286] Wed, 16 July 2014 01:27 Go to previous messageGo to next message
messages@element14.co
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Hi Zelos, There may be situations where you can let the pins float without any consequences. For example I often use ICs that have multiple repeated logic circuits or op amps of which I only want to use a couple. I do not ground the rest of the pins but just let them float. If a pin is involved in the section of the circuit that I am using then it is more important to ground it or pull it high depending on the circumstances. Inputs are particularly susceptable to niose and may cause problems. Check your data sheet to find out more information on what to do with unused pins.JohnOriginal article at http://www.element14.com/community/message/120571?tstart=0#120571.

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Re: Low voltage but no ground [message #156363 is a reply to message #156286] Wed, 16 July 2014 03:56 Go to previous messageGo to next message
messages@element14.co
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Thank you both for the answer, I have been looking at the sheets, though not being used to reading those it is a bit of a jungle! Original article at http://www.element14.com/community/message/120583?tstart=0#120583.

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Re: Low voltage but no ground [message #156364 is a reply to message #156286] Wed, 16 July 2014 04:04 Go to previous messageGo to next message
messages@element14.co
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Let me get this straight waht you're sayingI assume you mean a spst switch, let's call them pin A and B10kΩ resistor connected to pin A, then the other side of the resistor to the positive end of the voltage source, then pin B connected to groundand when the switch doesn't form a connection between A and B it's on, but when pin A and B form a connection it is grounded? I am interested in a somewhat similar construction where I need an easy way to ground it but of course I am a bit nervous abotu causing a shortcircuit. Probably irrational but I always feel like that voltage and such want to crawl up parallel stuff even though it won't. I basicly got 3 pins I need to ground or put high voltage on and using different switches I want to amke so only some of them get high voltage value and the remaining ones remain grounded. But I feel that if I connect to a common ground as described that the voltage will go around and get to the other pins making them all on or all off with no variation.Original article at http://www.element14.com/community/message/120584?tstart=0#120584.

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Re: Low voltage but no ground [message #156380 is a reply to message #156286] Wed, 16 July 2014 16:05 Go to previous messageGo to next message
messages@element14.co
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     Your summary of the circuit described by Hampton is correct. This would hold your input pin high with the resistor until the button is pushed and then the pin would go low. The only side effect is that most switches bounce (turn on and off for a few micro seconds) and this can cause problems for some logic circuits. Above I have drawn a simple debounce circuit that will help to eliminate the bounce effect. This circuit also holds the input high until the switch is closed. You can also rearrange the circuit so that the input pin is held low until the switch is closed if this better suits your needs.      Electricity always flows from a higher potential (voltage) to a lower potential. If two pins are at the same voltage, whether it is high or low no current will flow. Therefore you can be confident that all the pins that are tied to the ground will have no current flow between them. Likewise all the pins that are high at Vcc will have the same potential and no current will flow between them either. I do not know what type or specific chip you are using but for the most part they are pretty forgiving of having their inputs and outputs pulled high or low. It is important that the power in Vcc and ground 0V be on the proper pins. Also most circuits are quite sensitive to high voltage static that can be generated on your body by moving or walking. Be mindful of proper grounding procedures so you do not destroy your components.     The above circuit can be further improved by adding a Schmitt trigger or two on the output.     Hope this clarifies our answers for you.JohnOriginal article at http://www.element14.com/community/message/120635?tstart=0#120635.

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Re: Low voltage but no ground [message #156381 is a reply to message #156286] Wed, 16 July 2014 16:39 Go to previous messageGo to next message
messages@element14.co
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The resistor acts as a current load so it draws power from the supply but does not short.Original article at http://www.element14.com/community/message/120625?tstart=0#120625.

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Re: Low voltage but no ground [message #156382 is a reply to message #156286] Wed, 16 July 2014 16:40 Go to previous messageGo to next message
messages@element14.co
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It answers alot thank you! I drew my own sketch with 3 switches isntead nad 3 outputs, I want the 3 switches to only affect their given output, SW-1 affects O1 and so on, I got a feeling that B is the most likely correct one as it would make such resistence for current to move up any of the others that it simply won't but please do tell me if either one is correct, none or it simply doesn't matter. Open = Low, Closed = High for this circuit [IMG]http://i1310.photobucket.com/albums/s644/EmperorZelos/IMG_0665_zpsbd65178d.jpg[/IMG]Also what are the exact grounding procedures?Original article at http://www.element14.com/community/message/120641?tstart=0#120641.

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Re: Low voltage but no ground [message #156383 is a reply to message #156286] Wed, 16 July 2014 16:41 Go to previous messageGo to next message
messages@element14.co
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Registered: March 2013
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Thanks! I figured that was the purpose of the resistor to ensure it not shorting out but all the help is greatly appriciated!Original article at http://www.element14.com/community/message/120642?tstart=0#120642.

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Re: Low voltage but no ground [message #156384 is a reply to message #156286] Wed, 16 July 2014 16:42 Go to previous messageGo to next message
messages@element14.co
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Your welcomeOriginal article at http://www.element14.com/community/message/120643?tstart=0#120643.

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Re: Low voltage but no ground [message #156385 is a reply to message #156286] Wed, 16 July 2014 18:24 Go to previous messageGo to next message
messages@element14.co
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Registered: March 2013
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Hi Zelos,Drawing "A" is wrong as all your switches are in parallel and closing any one of them will pull all your inputs down to ground. Drawing "B" will work just fine as long as switch bounce isn't an issue in your application. Also the way you have it drawn your pins will be held low by the 10K resistors until a switch is closed and then that input will be held high by the switch. Since the switch has almost zero resistance the 10k resistor becomes irrelevant when the switch is closed. The purpose of the resistor is to hold the pin low (or high depending on the arrangement of the circuit) so that it doesn't float and introduce random inputs when the switch isn't closed. By using the resistor we get a solid High or Low depending on whether the switch is closed or not.JohnOriginal article at http://www.element14.com/community/message/120660?tstart=0#120660.

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Re: Low voltage but no ground [message #156386 is a reply to message #156286] Wed, 16 July 2014 18:28 Go to previous messageGo to next message
messages@element14.co
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Registered: March 2013
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I remember the nounce I made a wuick one just to see it, I had a feeling B would be best, what capactiance is needed to reduce the "bounce"?Original article at http://www.element14.com/community/message/120646?tstart=0#120646.

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Re: Low voltage but no ground [message #156387 is a reply to message #156286] Wed, 16 July 2014 18:46 Go to previous messageGo to next message
messages@element14.co
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Registered: March 2013
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You also asked about grounding procedures. Your power supply has two connections. The + (positive) terminal is considered the Vcc or High or supply voltage and the - (negative) is considered the 0 (zero) volt or Vdd or Ground. When we talk about grounding parts of the circuit we may just mean connecting that pin to the negative wire from the voltage source. On most circuits these 2 connection points, the supply voltage and the ground( zero volt) are made into a wire or a trace that can be easily accessed from all the components. Sometimes these are called rails. The connection point that is considered the 0V (zero volt) is considered the ground. There are many integrated circuits that need a positive voltage and a negative voltage and also a point that sits right in the middle at 0V (zero volts). In this case we have 3 rails or connection points. One would be, for example +5 volts, another -5 volts and the third would be 0 volts or ground.  This designations are all relative to each other.  We pick the rail that we want to call 0 volts and then the others are just measured relative to it. In my last example if we chose to call the rail that was -5 volts our new 0 v (zero volt) rail and put our test meter's negative probe on it we would find that measuring to the previous 0 volt rail would give us a reading of +5 volts and reading to our previous +5 volt rail would give us +10 volts. When you design a circuit you decide these conventions to suit the type and needs of the components that you will use. One final point has to do with what is called Earth Ground. Earth Ground is an actual connection to the Earth or other extremely large entity capable of sinking electrical charge. In some circuits this connection to Earth is very important to eliminate noise and interference. In a situation where an Earth Ground is important we connect the rail that we have designated as 0 volts to the Earth, usually,  through the ground terminal on our electrical wall outlets.JohnOriginal article at http://www.element14.com/community/message/120661?tstart=0#120661.

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Re: Low voltage but no ground [message #156389 is a reply to message #156286] Wed, 16 July 2014 18:49 Go to previous messageGo to next message
messages@element14.co
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Very informative which while helpful in overall understanding I got a feeling it might not be the issue at hand
o most circuits are quite sensitive to high voltage static that can be generated on your body by moving or walking. Be mindful of proper grounding procedures so you do not destroy your components.
as I understood this you indicate some procedure to ground yourself in order to prevent discharge by the human body and I am wondering about a suitible manner to do that, or did I missunderstand?Original article at http://www.element14.com/community/message/120647?tstart=0#120647.

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Re: Low voltage but no ground [message #156390 is a reply to message #156286] Wed, 16 July 2014 18:52 Go to previous messageGo to next message
messages@element14.co
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It doesn't have to be very big. In the circuit I drew it is 10 nano Farads or .01 uF. All the capacitor does is to moderate any make and break that the switch does when it snaps closed. If you still have trouble with bounce there are more sophisticated circuits available. If we didn't have circuits to debounce switches you would get multiple characters on the screen every time you push a key on your computer's keyboard.JohnOriginal article at http://www.element14.com/community/message/120662?tstart=0#120662.

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Re: Low voltage but no ground [message #156391 is a reply to message #156286] Wed, 16 July 2014 19:02 Go to previous messageGo to next message
messages@element14.co
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IC's that are CMOS are very sensitive to static. This is why they come packed in antistatic bags and foam. When I work with them I am just mindful of the potential danger. I will touch something that I know is Earth Ground before I handle the chip and I will consciously not slide around in my chair a lot. If you are doing a lot of work with sensitive chips or boards there are antistatic sprays for the carpet, and antistatic wrist straps that can be connected to ground. Working on a surface that is antistatic can also help. Don't get too paranoid about this but just be aware of it. If you live in an area that has high humidity static is less of a problem. I live where it gets real cold and dry in the winter so we get static without doing anything. If you are working with the older TTL chips static isn't quite as big a concern.Original article at http://www.element14.com/community/message/120663?tstart=0#120663.

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Re: Low voltage but no ground [message #156392 is a reply to message #156286] Wed, 16 July 2014 19:04 Go to previous messageGo to next message
messages@element14.co
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Would a normal sink by any chance classify as grounded? I have vague memroies of it being such Also, thank you so much! You've enlightened me greatly and it is greatly appriciated!Original article at http://www.element14.com/community/message/120649?tstart=0#120649.

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Re: Low voltage but no ground [message #156393 is a reply to message #156286] Wed, 16 July 2014 19:15 Go to previous messageGo to next message
messages@element14.co
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I assume you mean a kitchen sink. This is probably not the best choice. There is too much plastic being used in the plumbing now days. If you see copper pipe and you can trace it back to where it goes into the ground and is still copper, then perhaps. The next challenge is to get a good connection to the copper pipe. I do not know where you live and what the codes are. If there is an electrical ground in your home then all the properly wired outlets will have a ground connection. Most appliances with a three wire plug will have their outer metal structures connected to the home electrical ground.JohnOriginal article at http://www.element14.com/community/message/120666?tstart=0#120666.

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Re: Low voltage but no ground [message #156394 is a reply to message #156286] Wed, 16 July 2014 19:35 Go to previous messageGo to next message
messages@element14.co
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thank you, you've answered everything and more Original article at http://www.element14.com/community/message/120654?tstart=0#120654.

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Re: Low voltage but no ground [message #156400 is a reply to message #156286] Thu, 17 July 2014 05:30 Go to previous messageGo to next message
messages@element14.co
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A quick question, for the resistors, does it matter if it is more than 10k?Original article at http://www.element14.com/community/message/120693?tstart=0#120693.

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Re: Low voltage but no ground [message #156412 is a reply to message #156286] Thu, 17 July 2014 13:53 Go to previous messageGo to next message
messages@element14.co
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You want the resistor to be << than the Zin of the chip.  The RC product is what determines the behavior.  That is an awfully simple debounce circuit, its appropriateness varies by the situation.  John mentions split supplies.  Usually, with op-amp circuits, V+ and V- run the circuit, and the split between them goes to a point in the circuit. I think you are confusing the label for 0V that we use in circuits and call ground, and chassis ground, which has to do with the water pipes.  More moieties than labels in electronics sometimes, it's confusing.Original article at http://www.element14.com/community/message/120725?tstart=0#120725.

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Re: Low voltage but no ground [message #156413 is a reply to message #156286] Thu, 17 July 2014 13:55 Go to previous messageGo to next message
messages@element14.co
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What is Zin here?Original article at http://www.element14.com/community/message/120726?tstart=0#120726.

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Re: Low voltage but no ground [message #156414 is a reply to message #156286] Thu, 17 July 2014 14:21 Go to previous messageGo to next message
messages@element14.co
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That would be dependent on the architecture of your chip, it's on the datasheet.  CMOS, maybe you could go a little higher.  Obsolescent  TTL was hi-Z in the high state and lo-Z in the low state, but it worked out because the drivers were asymmetrical as well.  This is where the convention of having our switches pull low comes from. To say that at a point in a circuit zero current flows is a fairly unambiguous statement.  Charge carriers, if they are about, are as likely to drift one way as the other.  No net motion.  To say that a point in a circuit is at zero volts merely states that it is at equal potential to another point in the circuit that we have chosen to label as zero volts.Original article at http://www.element14.com/community/message/120730?tstart=0#120730.

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Re: Low voltage but no ground [message #156415 is a reply to message #156286] Thu, 17 July 2014 14:27 Go to previous messageGo to next message
messages@element14.co
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Many if not most datasheets are going to discuss input current or input leakage current rather than Zin.  Knowing the PS (power supply) potential allows us to infer Zin.  Sometimes, if the chip can operate over a range of potentials, the information is given in a chart rather than a table.  I really recommend re-reading your data sheet, looking up everything you don't understand, 'til it soaks in.Original article at http://www.element14.com/community/message/120746?tstart=0#120746.

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Re: Low voltage but no ground [message #156416 is a reply to message #156286] Thu, 17 July 2014 14:29 Go to previous messageGo to next message
messages@element14.co
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Discussing things here sure do help alot Original article at http://www.element14.com/community/message/120747?tstart=0#120747.

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Re: Low voltage but no ground [message #156417 is a reply to message #156286] Thu, 17 July 2014 16:33 Go to previous message
messages@element14.co
Messages: 563
Registered: March 2013
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You would also want the external capacitor that John has drawn to be >> than the input capacitance (this will be in the datasheet) of the device, so you won't have to reckon it in (it is in shunt with the external capacitor, so their values sum) to the timing or deal with its potential non-linearities, production spread.Original article at http://www.element14.com/community/message/120755?tstart=0#120755.

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