Introduction

A 7 segment IC (integrated circuit) is a common component used in electronic devices to display numerical information. It contains 7 LED segments arranged in the shape of an 8 to represent numbers 0-9. Cracking or reverse engineering a 7 segment IC involves understanding its internal structure and logic to recreate its functionality. This can be useful for repairing devices, learning about circuits, or cloning an IC. In this comprehensive guide, we will discuss the steps to crack a 7 segment IC.

Overview of 7 Segment IC

• A 7 segment IC has 8 pins – 7 pins for each LED segment and 1 pin for the common cathode/anode.
• The 7 LEDs are arranged in the shape of number 8 with 2 vertical, 3 horizontal and 2 diagonal segments.
• By lighting up specific LED segments, it can represent numerals from 0 to 9.
• It contains internal circuitry with logic gates and decoders to convert binary inputs into segment selection.
• Common cathode 7 segment IC has the cathode pins of LEDs connected together while common anode has the anode pins connected.
• Additional pins may be present for features like decimal points.

Steps to Crack 7 Segment IC

1. Identify package type and pinouts

• The first step is to identify the package style – whether it is dual in-line or single in-line.
• Next, determine the pinout configuration from the datasheet.
• This gives the mapping between pins and internal segments.
• For common cathode 7 segment:
  • Pin 1-7: individual LED segments a-g
  • Pin 8: common cathode
• For common anode:
  • Pin 1-7: segments
  • Pin 8: common anode

2. Connect test circuit

• Build a test circuit with the 7 segment IC, current limiting resistors and power supply.
• Use ~5-10mA current limiting resistors for each segment.
• Connect common cathode/anode to ground or Vcc respectively.
• Initially, short all non-common pins together and connect to Vcc/ground. This lights up all segments to test.

Test circuit with 7 segment IC

3. Analyze internal segments

Now comes the crucial step of identifying each internal segment within the IC.

• First, connect one segment pin directly to Vcc/ground. The corresponding segment should light up.
• Repeat this for all pins to map pins and segments.
• Alternatively, short all pins except one to light up the segment.
• Mark the internal LED segments a-g in clockwise order on the IC diagram.

4. Determine cathode/anode

• Next, figure out whether the IC has a common cathode or common anode:
  • If shorting a segment to ground lights it up, it is common cathode.
  • If shorting to Vcc lights it up, it is common anode.
• Connect the identified common pin to Vcc for common cathode IC and to ground for common anode.

5. Connect decoder/driver circuitry

Now that the internal segment pins are known, external circuitry can be added to drive the 7 segment IC and display numbers:

• A BCD to 7 segment decoder IC can convert binary inputs to LED segment selection.
• Connect 4-bit BCD input pins to decoder and its outputs to the 7 segment common anode/cathode pins.
• A microcontroller can also be programmed to drive the 7 segment directly.
• 7 GPIO pins of the microcontroller can connect to the 7 segment pins with voltage divider circuits.
• Software loops through number patterns and outputs bit sequence to generate digits.

Example Circuits

Here are some example circuits to use the cracked 7 segment IC in projects:

BCD to 7 segment decoder

This uses 4-bit BCD input to drive a common anode 7 segment through a BCD to 7 segment decoder IC like the 7447.

Microcontroller driven 7 segment

A microcontroller like Arduino can directly drive the 7 segment IC through voltage divider circuits on the output GPIO pins.

Pros and Cons of Cracking 7 Segment IC

Pros:

• Learn internal working of 7 segment ICs
• Repurpose ICs from old devices
• Customize segments for unique projects needs
• No need to buy new ICs

Cons:

• Time consuming process
• Risk of damage to IC
• Requires understanding of circuits and logic
• Not feasible for complex ICs

Frequently Asked Questions

1. How many pins does a common anode 7 segment have?

A common anode 7 segment display has 8 pins. 7 pins for the individual LED segments and 1 pin for the shared anode connection.

2. What tools are required to crack a 7 segment IC?

Basic electronic tools like a digital multimeter, breadboard, jumper wires, resistors, power supply and datasheets are required. A magnifying glass can also help in identifying tiny IC package markings.

3. Is it possible to damage a 7 segment while cracking it?

Yes, it is possible to damage the IC if currents exceed the absolute maximum ratings. Care should be taken to limit the current through each segment to 5-10mA. The common cathode/anode pins should also be at correct voltages.

4. How to identify pin 1 of the IC package?

For dual in-line packages, pin 1 is indicated by a notch or dot at one end of the IC. For single in-line packages, a dot or notch indicates the cathode or anode side. The datasheet also contains the pin diagram.

5. Can a common cathode IC be converted into common anode?

It is generally not possible to convert between common cathode and anode configurations within a 7 segment IC. The internal bonding of LED cathodes or anodes is fixed during IC fabrication. External circuits can be used to drive a cathode IC from an anode output.

Conclusion

Cracking a 7 segment IC involves identifying internal segments, cathode/anode, pinouts and then interfacing it with decoder ICs or microcontrollers. It helps gain insights into IC functionality and reuse old display ICs in custom projects. With an organized approach and necessary precautions, hobbyists can successfully reverse engineer display ICs for unique applications.