74LS08 IC is a member of 74XXYY IC series. There are four AND gates in the chip and each gate have two inputs, hence the name. 74LS SN74LS08NSR. ACTIVE. SO. NS. Green (RoHS. & no Sb/Br). CU NIPDAU. LevelC-UNLIM. 0 to 74LS SN74S08D. ACTIVE. Note The ”Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaran- teed The device should not be operated at.

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The chip is used in systems where high speed AND operation is needed.

digital logic – 74LS08 AND gate always outputting high? – Electrical Engineering Stack Exchange

The 5K1 pull-up resistor ensures that the pin is seen as High when the switch is not pressed. With that the drop across resistor R1 will be zero. If you want to absolutely avoid learning the pin out of these push buttons, always connect them in diagonal.

This LED is connected to detect the state of output. In that case, the left button should have a red wire on the lower left pin.

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The four AND gates in the chip mentioned earlier are connected internally as shown in diagram below. The switch between the input pin and Ground will provide a Zero Ohm connection to Ground when the switch is pressed, ensuring that the gate sees the input as a Low. Pressing the buttons does nothing. There are four legs connected together in pair of two.


74LS08 – Quad 2-In AND Gate

Home Questions Tags Users Unanswered. When both buttons are not pressed. The chip is available in different packages and is chosen depending on requirement. By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Sara Heart 1 6. You might be using push buttons that are connected in such a way that the legs are shorted connected together.

Submitted by admin on 6 April In the circuit two transistors are connected in series to form a AND gate.

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TL — Programmable Reference 7l4s08. The description for each pin is given below. In this state the current flow through base of both transistors will be zero.

The chip is basically used where AND logic operation is needed. I am new to electrical engineering still so forgive me if I am making a stupid mistake.

It is 74,s08 popular and is available everywhere.

Because output is nothing but voltage across resistor R1 it will be LOW. Output of the AND gate is the voltage across resistor R1. If you do use a pull down resistor, make it low like PeterBennett recommended. It is currently powered by a 5v 1. Simon Marcoux 1, 2 By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

As you can see the LED is on by default despite neither button being pressed. I think that you were dead on in the first place with your answer SaraHeart.


As AlmostDone said, you need to draw about 1. With the LS you need to sink ajd. Looking at the image I agree. I have tried switching to a 9v battery and nothing changes. The inputs of the 74LS family and other TTL versions source significant current and will appear as a logic High unless firmly pulled to Ground – your k resistors won’t help.

It might be oscillating as well. These two inputs are connected to buttons to change the logic of inputs. After verifying 74sl08 three states, you can tell that we have satisfied the above truth table.

Sign up using Email and Password. When any one of the buttons is pressed. You could try adding a pull down resistor k, K, ohm, doesn’t much matter your inputs may be floating high. Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

Many pins left floating. Both transistors will be ON and voltage across both of them will be zero. If you choose the wrong pair, you end up with an always on switch.

Last modified: April 29, 2020