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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74LS08 Datasheet

In the circuit two transistors are connected in series to form a AND gate. Sign up using Facebook. The chip provides TTL outputs which are needed in some systems. The inputs with both switches unpressed allow the pins to float around, depending on the way 74ks08 IC is set-up internally.

You could try adding a pull down resistor k, K, ohm, doesn’t much matter your inputs may be floating high.

This LED is connected to detect the state of output. Many pins left floating.

It might be oscillating as well. When any one of the buttons is pressed. The chip is available in different packages and is chosen depending on requirement.

Then if your IC is good your switches are mis-wired, I have done it myself with that type of switch. Email Required, but never shown. Output of the AND gate is the voltage across resistor R1. After verifying the three states, you can tell 74lss08 we have satisfied the above truth table.


For realizing the above truth table let us take a simple AND gate application circuit as shown below. With the LS you need to sink 1.

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It is currently powered anf a 5v 1. Because of this the chip can be used for high speed AND operations. Post as a guest Name. They are notorious for that particular mishap.

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Something similar should be done to the right button. Both transistors will be ON and voltage across both of them will be zero.

Pressing the buttons does nothing. Looking at the image I agree. Sara Heart 1 6. The chip is basically used where AND logic operation is needed. There are four legs connected together in pair of two. In this state the current flow through base of both transistors will be zero. With that the drop across resistor R1 will be zero. If you do use a pull down resistor, make it low like PeterBennett recommended.

The 5K1 pull-up resistor wnd that the pin is seen as High when the switch is not pressed. I think that you were dead on in the first place with your answer SaraHeart.


TL — Programmable Reference Voltage. The 74ls80 AND gates in the chip mentioned earlier are connected internally as shown in diagram below. As AlmostDone said, you need to draw about 1. It is really popular and is available 74lls08. Because output is nothing but voltage across resistor R1 it will be LOW. When both buttons are not pressed.

Because total VCC appears across transistors the drop across resistor R1 will be zero. As you can see the LED is on by default despite neither button being pressed. Home Questions Tags Users Unanswered.

When both buttons are pressed. Post Your Answer Discard By clicking “Post Your Answer”, you amd 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. You might be using push buttons that are connected in such a way that the legs are shorted connected together.

Simon Marcoux 1, 2 There are four AND gates in the chip, we can use one or all gates simultaneously.