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 – Quad 2-In AND Gate

Home Questions Tags Users Unanswered. The inputs with both switches unpressed allow the pins to float around, depending on the way the IC is set-up internally. The inputs of the 74LS 74lz08 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. At this time the total VCC appears across resistor R1. These two inputs are connected to buttons to change the logic of inputs.

As AlmostDone said, you need to draw about 1. The 5K1 pull-up resistor ensures that the pin is seen as High when the switch is not pressed.


Many pins left floating. The circuit working can be explained in few stages below: When 74ls0 buttons are pressed. Submitted by admin on 6 April The chip is basically used where AND logic operation is needed. Sign up using Email and Password.

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

74LS08 – Quad 2-In AND Gate

The two inputs of AND gate are driven out from bases of the two transistors. It might be oscillating as well. And after a google search I havnt come up with anything, usually the videos are terrible quality or they are using a different AND gate. Because total VCC 74sl08 across transistors the drop across resistor R1 will be zero. With the LS you need to sink 1. With that the drop across resistor R1 will be zero. You might be using push buttons 74l0s8 are connected in such a way that the legs are shorted connected together.

Pull down resistors as suggested in another answermight also a good idea. Pressing the buttons does nothing. The description for each pin is given below. This LED is connected to detect the state of output. Because of this the chip can be used for high speed AND operations. Both transistors will be ON and voltage across both of them 74le08 be zero. TL — Programmable Reference Voltage.

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. After verifying the three states, you can tell that we have andd the above truth table.

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The chip provides TTL outputs which are needed in some systems.

The chip is available in different packages and is chosen depending on requirement. As you can see the LED is on by default despite neither button being pressed.

There are four legs connected together in pair of two. The inputs on CMOS parts anything with a “C” in the middle source or sink very little current, so K pull-up or -down will work with them. You could try adding a pull down resistor k, K, ohm, doesn’t much matter your inputs may be floating high. In this state the current flow through base of both transistors will be zero. When both buttons are not pressed. Looking at the image I agree.

I have tried switching to a 9v battery and nothing changes.

Circuito integrado – Wikilibros

Something similar should be done to the right button. When any one of the buttons is pressed. Output of the AND gate is the voltage across resistor R1. A few mentioned below.

In the circuit two transistors are connected in series to form a AND gate. Sara Heart 1 6.

Author: admin