Use a decoupling capacitor

Oct 13, 2025 by wbrum.org 87 views

Introduction

When building complex electronic projects, such as a split flap clock with four 28BYJ-48 stepper motors, one of the most frustrating issues to encounter is cross-talk between components. In this article, we will delve into the weird cross-talk issues that can arise when using the ULN2003 and 28BYJ-48 stepper motors, and explore possible solutions to mitigate these problems.

Background

A split flap clock is a type of display that uses a series of flaps to display time and other information. Each flap is typically driven by a stepper motor, which allows for precise control over the movement of the flap. In this project, we are using four 28BYJ-48 stepper motors, each connected to a ULN2003 driver IC. The ULN2003 is a high-current Darlington transistor array that can drive a wide range of loads, making it an ideal choice for driving stepper motors.

The Problem

At first glance, the setup seems straightforward: each motor is connected to a ULN2003 driver IC, which is then connected to the ESP32 microcontroller. However, as soon as we start running the motors, we notice a strange phenomenon: the motors seem to be "talking" to each other. When one motor is running, it causes the other motors to behave erratically, as if they are being driven by an external signal.

Symptoms

The symptoms of this cross-talk issue are varied and can be quite frustrating to diagnose. Some of the common symptoms include:

Motor jitter: When one motor is running, the other motors may start to jitter or oscillate, even if they are not being driven.
Motor skipping: In some cases, the motors may skip steps or move erratically, as if they are being driven by an external signal.
Motor stall: When the cross-talk issue is severe, the motors may stall or become stuck, requiring a manual reset.

Possible Causes

So, what could be causing this weird cross-talk issue? After some investigation, we have identified several possible causes:

Electrical noise: One of the most common causes of cross-talk is electrical noise, which can be generated by the motors, the ULN2003 driver ICs, or even the ESP32 microcontroller.
Grounding issues: If the grounding of the motors, the ULN2003 driver ICs, or the ESP32 microcontroller is not proper, it can cause cross-talk between the components.
Capacitive coupling: Capacitive coupling can occur when two components are connected through a common ground or power supply, allowing electrical signals to be transmitted between them.

Solutions

So, how can we mitigate these cross-talk issues? Here are some possible solutions:

Use a decoupling capacitor: Adding a decoupling capacitor between the power supply and the ULN2003 driver IC can help to filter out electrical noise and reduce cross-talk.
Use a common ground: Ensuring that all components, including the motors, the ULN2003 driver ICs, and the ESP32 microcontroller, are connected to a common ground can help to reduce cross-talk.
Use a shielded cable: Using a shielded cable to connect the motors to the ULN2003 driver ICs can help to reduce capacitive coupling and electrical noise.
Use a motor driver with built-in noise reduction: Some motor drivers, such as the DRV8825, have built-in noise reduction features that can help to mitigate cross-talk issues.

Implementation

To implement these solutions, we can make the following changes to our PCB design:

Add a decoupling capacitor: We can add a decoupling capacitor between the power supply and the ULN2003 driver IC to filter out electrical noise.
Use a common ground: We can ensure that all components, including the motors, the ULN2003 driver ICs, and the ESP32 microcontroller, are connected to a common ground.
Use a shielded cable: We can use a shielded cable to connect the motors to the ULN2003 driver ICs to reduce capacitive coupling and electrical noise.
Use a motor driver with built-in noise reduction: We can replace the ULN2003 driver ICs with motor drivers that have built-in noise reduction features.

Conclusion

In conclusion, cross-talk issues between the ULN2003 and 28BYJ-48 stepper motors can be a frustrating problem to diagnose and solve. However, by understanding the possible causes of this issue and implementing the solutions outlined above, we can mitigate these problems and ensure that our split flap clock project runs smoothly and accurately.

Future Work

In the future, we plan to explore other possible causes of cross-talk issues, such as electromagnetic interference (EMI) and radio-frequency interference (RFI). We also plan to investigate the use of other motor drivers and noise reduction techniques to further improve the performance of our split flap clock project.

References

[1] ULN2003 datasheet
[2] 28BYJ-48 stepper motor datasheet
[3] ESP32 datasheet
[4] DRV8825 datasheet

Appendix

A. ULN2003 Pinout

Pin	Function
1	VCC
2	GND
3	IN1
4	IN2
5	IN3
6	IN4

B. 28BYJ-48 Stepper Motor Pinout

Pin	Function
1	VCC
2	GND
3	A
4	B
5	C
6	D

C. ESP32 Pinout

Pin	Function
1	VCC
2	GND
3	TX
4	RX
5	SCL
6	SDA

D. DRV8825 Pinout

Pin	Function
1	VCC
2	GND
3	SCL
4	SDA
5	STEP
6	DIR

Introduction

In our previous article, we explored the weird cross-talk issues that can arise when using the ULN2003 and 28BYJ-48 stepper motors in a split flap clock project. We discussed possible causes of this issue, including electrical noise, grounding issues, and capacitive coupling. We also outlined solutions to mitigate these problems, such as using a decoupling capacitor, a common ground, a shielded cable, and a motor driver with built-in noise reduction.

Q&A

Q: What is cross-talk, and why is it a problem in my split flap clock project?

A: Cross-talk is the phenomenon where electrical signals are transmitted between components through a common ground or power supply, causing erratic behavior in the motors. This can lead to motor jitter, skipping, or stalling, which can be frustrating to diagnose and solve.

Q: What are the possible causes of cross-talk issues in my split flap clock project?

A: The possible causes of cross-talk issues include electrical noise, grounding issues, and capacitive coupling. Electrical noise can be generated by the motors, the ULN2003 driver ICs, or even the ESP32 microcontroller. Grounding issues can occur if the grounding of the motors, the ULN2003 driver ICs, or the ESP32 microcontroller is not proper. Capacitive coupling can occur when two components are connected through a common ground or power supply, allowing electrical signals to be transmitted between them.

Q: How can I mitigate cross-talk issues in my split flap clock project?

A: To mitigate cross-talk issues, you can use a decoupling capacitor, a common ground, a shielded cable, or a motor driver with built-in noise reduction. Adding a decoupling capacitor between the power supply and the ULN2003 driver IC can help to filter out electrical noise. Ensuring that all components, including the motors, the ULN2003 driver ICs, and the ESP32 microcontroller, are connected to a common ground can help to reduce cross-talk. Using a shielded cable to connect the motors to the ULN2003 driver ICs can help to reduce capacitive coupling and electrical noise. Finally, using a motor driver with built-in noise reduction can help to mitigate cross-talk issues.

Q: What are some common symptoms of cross-talk issues in my split flap clock project?

A: Some common symptoms of cross-talk issues include motor jitter, skipping, or stalling. Motor jitter can cause the motors to oscillate or vibrate, while motor skipping can cause the motors to move erratically or skip steps. Motor stalling can cause the motors to become stuck or unable to move.

Q: How can I diagnose cross-talk issues in my split flap clock project?

A: To diagnose cross-talk issues, you can use a multimeter to measure the voltage and current at various points in the circuit. You can also use a logic analyzer to monitor the signals at the ESP32 microcontroller and the ULN2003 driver ICs. Additionally, you can use a oscilloscope to visualize the electrical signals and identify any anomalies.

Q: What are some best practices for designing a split flap clock project to minimize cross-talk issues?

A: Some best practices for designing a split flap clock project to minimize cross-talk issues include using a common ground, using a shielded cable, and using a motor driver with built-in noise reduction. Additionally, you can use a decoupling capacitor to filter out electrical noise, and ensure that all components are properly grounded.

Conclusion

In conclusion, cross-talk issues can be a frustrating problem to diagnose and solve in a split flap clock project. However, by understanding the possible causes of this issue and implementing the solutions outlined above, you can mitigate these problems and ensure that your project runs smoothly and accurately.

Additional Resources

[1] ULN2003 datasheet
[2] 28BYJ-48 stepper motor datasheet
[3] ESP32 datasheet
[4] DRV8825 datasheet
[5] Decoupling capacitor datasheet
[6] Shielded cable datasheet
[7] Motor driver with built-in noise reduction datasheet