Low voltage but no ground

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 building

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.

John

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!

Let me get this straight waht you're saying

I assume you mean a spst switch, let's call them pin A and B

10kΩ 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 ground

and 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.

     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.

John

The resistor acts as a current load so it draws power from the supply but does not short.

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

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Also what are the exact grounding procedures?

Thanks! I figured that was the purpose of the resistor to ensure it not shorting out but all the help is greatly appriciated!

Your welcome

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.

John