The 74138 ic device is a popular 3 to 8 line decoder IC used in many digital logic circuits. Knowing how to bypass or “crack” this ic can be useful for learning purposes, but should not be done unlawfully. This article provides instructions on how to crack the 74138 ic.

Gather the Required Equipment

To crack the 74138 ic, you will need the following equipment:

• 74138 ic chip
• Breadboard
• Jumper wires
• 5v power supply
• Multimeter
• Oscilloscope (optional)

Breadboard

The breadboard allows you to easily connect the 74138 ic and other components. Make sure to insert the ic into the breadboard properly, matching the pin layout.

Jumper Wires

Use jumper wires to make connections between the ic pins and power supply on the breadboard.

Power Supply

You need a 5v DC power supply to provide power to the ic. Make sure it can supply enough current for the chip.

Multimeter

A multimeter allows you to measure the input and output voltages and signals. This is useful for debugging the circuit.

Oscilloscope

An oscilloscope is optional but allows you to visualize the digital signals. This can help troubleshoot any issues.

Connect Power and Inputs

Follow this wiring diagram to connect power and inputs to the 74138 ic:

• Connect pin 1 to ground
• Connect pin 2 to 5v power
• Connect pins 3-5 to toggle switches or push buttons for inputs A0-A2
• Connect pins 6-8 to ground (active low)

This provides the required power and inputs to the ic.

Monitor the Outputs

The 74138 ic has 8 output pins marked Y0 to Y7. Connect LEDs with resistorsto these output pins to visually see which output is active based on the input code.

You can also use a multimeter or oscilloscope on the output pins to analyze the signals.

Crack the IC

To crack or bypass the 74138 ic:

• Apply 5v power to pin 1 instead of ground. This disables the internal logic.
• Ground pins 6-8. This activates all the outputs simultaneously.
• Toggle the A0-A2 inputs and observe that all outputs stay active regardless of input code. This shows that the internal logic has been bypassed.

By powering up the chip incorrectly and grounding the enable pins, you can override the internal logic and get access to all outputs at once.

Troubleshooting Tips

• Double check your wiring against the pinout diagram
• Make sure power supply is delivering 5v
• Check that enable pins (6-8) are grounded
• Check for shorts between jumper wires

Cracking the 74138 ic takes some careful wiring but allows you to understand how the internal logic works. Just remember to use this knowledge responsibly.

Summary

• Gather the required equipment like breadboard, jumper wires, ic chip etc.
• Connect power supply and inputs to the 74138 ic as per the pin diagram
• Monitor the outputs using LEDs or an oscilloscope
• To crack the ic, power up incorrectly and ground the enable pins
• This overrides the internal logic and gives access to all outputs
• Use troubleshooting tips to fix any incorrect wiring issues

Frequently Asked Questions

Q: What is the 74138 ic used for?

A: The 74138 ic is a 3 to 8 line decoder. It takes a 3-bit binary input and activates one of the 8 output lines accordingly.

Q: What precautions should I take when cracking the 74138?

A: Use proper wiring techniques to avoid shorts. Make sure not to exceed the max supply voltage and load currents for the ic. Only crack it for learning purposes.

Q: Do I need an oscilloscope or can I just use LEDs?

A: You can just use LEDs to visually monitor the outputs. An oscilloscope is helpful but optional for this experiment.

Q: What is the enable input on the 74138 used for?

A: The enable input (pins 6-8) controls whether the decoder is active or not. Grounding this disables the internal logic.

Q: How do I know if I have wired up the 74138 correctly?

A: Double check the pin diagram. Monitor the outputs – only one LED should light up at a time for different input codes. If multiple LEDs light incorrectly, check your wiring.