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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These two inputs are connected to buttons to change the logic of inputs. This LED is connected to detect the state of output.

74LS08 Pinout, Configuration, Equivalents, Circuit & Datasheet

The four AND gates in the chip mentioned earlier are connected internally as shown in diagram below. Home Questions Tags Users Unanswered.

When both buttons are not pressed. Sign up or log in Sign up using Google. Many pins left floating. Both transistors will be ON and voltage across both of them will be zero. As AlmostDone said, you need to draw about 1. Sara Heart 1 6.

At this time the total VCC appears across resistor R1. It might be oscillating as well. The chip is used in systems where high speed AND operation is needed. As you can see the LED is on by default despite neither button being pressed. Because output is nothing but voltage across resistor R1 it will be LOW.

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The inputs with both switches unpressed allow the pins to float around, depending on the way the IC is set-up internally. Email Required, but never shown. 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. By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

TL — Programmable Reference Voltage. With that the drop across resistor R1 will be zero. Output of the AND gate is the voltage across resistor R1.

74LS08 – Quad 2-In AND Gate

Because total VCC appears across transistors the drop across ahd R1 will be zero. And after a google search I havnt come up with anything, usually the videos are terrible 74la08 or they are using a different AND gate. Then if your IC is good your switches are mis-wired, I have done it myself with that type of switch.

For better understanding the internal working let us consider the simplified internal circuit of AND gate as shown below.

Pressing the buttons does nothing. The 5K1 pull-up resistor ensures that the pin is seen as High when the switch is not pressed. If you want to absolutely avoid learning the pin out of these push buttons, always connect them in diagonal. When any one of the buttons is 74sl08.

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Sign up using Email and Password. The inputs on CMOS parts anc with a “C” in the middle source or sink very little current, so K anr or -down will work with them. Because of this the chip can be used for high speed AND operations.


Pull down resistors as suggested in another answermight also a good idea. When both buttons are pressed. 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.

You could try adding a pull down resistor k, K, ohm, doesn’t much matter your inputs may be floating high. For realizing the wnd truth table let us take a simple AND gate application circuit as shown below.

I think that you were dead on in the first place with your answer SaraHeart. If you do use a pull down resistor, make it low like PeterBennett recommended. In that case, the left button should have a red wire on the lower left pin. If you choose the wrong pair, you end up with an always on switch. Submitted by admin on 6 April The chip provides TTL outputs which are needed in some systems.

Something similar should be done to the right button. In this state the current flow through base of both transistors will 74ls8 zero. Post as a guest Name. The two inputs of AND gate are driven out from bases of the two transistors. The description for each pin is given below.

Looking at the image I agree. You might be using push buttons that are connected in such a way that the legs are shorted connected together. Aand Marcoux 1, 2 A few mentioned below.

In the circuit two transistors are connected in series to form a AND gate.