Introduction

The CD4511 is a 7-segment display decoder driver that allows you to control 7-segment displays easily with a microcontroller. In this article, we’ll look at how to “crack” or hack the CD4511 chip to get more control over the individual segments.

Understanding the CD4511

The CD4511 takes in 4-bit binary coded decimal (BCD) values and drives the correct segments to display the number. It has 7 outputs, one for each segment (A-G), that can drive LED or incandescent displays directly.

The inputs are:

• BCD value to be displayed (D0-D3)
• Latch enable (LT) – latches the input value when pulsed low
• Blanking input (BI) – disables all segments when high

Hacking the Segment Outputs

To get more control, we need to override the internal BCD to 7-segment decoding. Here are some methods:

Method 1: Override BCD inputs

• Set LT low to constantly latch the BCD inputs
• Override D0-D3 pins with direct segment driving

For example:

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D0 - Segment A D1 - Segment B D2 - Segment C D3 - Segment D

Set the pins high/low to turn segments on/off.

Method 2: Override blanking input

• Set BI high to blank segments
• Override BI with pulse train to strobes segments

Generate pulses to rapidly turn segments on/off. Adjust pulse timing for brightness control.

Method 3: Interrupt supply lines

• Cut trace to segments and inject signals
• Allows complete control over each segment

More invasive, but enables fully independent segment control.

Sample Implementation

Here is an example using an Arduino to override the BCD inputs and control a 7-segment display:

cpp

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// Pins for 7 segment display int segA = 2; int segB = 3; int segC = 4; int segD = 5; void setup() { // Set segment pins as outputs pinMode(segA, OUTPUT); pinMode(segB, OUTPUT); pinMode(segC, OUTPUT); pinMode(segD, OUTPUT); // Override BCD inputs digitalWrite(segA, HIGH); digitalWrite(segB, LOW); digitalWrite(segC, HIGH); digitalWrite(segD, HIGH); } void loop() { // Flash segment B digitalWrite(segB, HIGH); delay(100); digitalWrite(segB, LOW); delay(100); }

This flashes segment B on and off independently. The other segments remain on.

Conclusion

With some simple hacking, the CD4511 chip can be leveraged in creative ways to gain more granular control over 7-segment displays. Overriding the inputs and blanking allows custom patterns and effects to be produced. Understanding how the chip works internally helps tremendously in determining the best way to modify its behavior.

FQA

What are the main ways to hack the CD4511 for more segment control?

The main methods are: overriding the BCD inputs, interrupting the blanking input, and physically cutting traces to intercept the segment supply lines.

What is a good way to create custom flashing effects?

Generating a pulse wave signal to override the blanking input is an easy way to strobe the segments on and off. Varying the pulse timing gives brightness control.

How do you override the BCD inputs?

Set the latch enable low to constantly latch the inputs. Then connect each BCD pin to a microcontroller pin controlling an individual segment.

Is it possible to control each segment completely independently?

Yes, by physically cutting the traces for each segment you can inject new signals and have full individual control.

What is the downside to interrupting the supply lines?

This method is more invasive than the others. It requires splicing wires and some reworking of the PCB. The segment driving capabilities are also reduced.