# The Spark Gap - Episode 20

- Show: [The Spark Gap](https://hardwarepodcasts.com/podcast/the-spark-gap)
- Published: 2014-10-29
- Length: 30m
- Page: https://hardwarepodcasts.com/podcast/the-spark-gap/2014-10-29-the-spark-gap-episode-20
- Listen: https://thesparkgap.net/the-spark-gap-episode-20

## Summary

Hosts Carl and Corey discuss lessons learned from discarding old PCBs, focusing on GPIO expanders, interconnect design, and power protection. They argue against using GPIO expanders due to weak drive strengths and timing gotchas, recommending larger microcontrollers instead. They detail the risks of non-symmetric daughter card connectors and the necessity of robust input power protection to prevent damage from incorrect adapters.

## Chapters

- [0:00](https://hardwarepodcasts.com/podcast/the-spark-gap/2014-10-29-the-spark-gap-episode-20#t=0) Introduction: Discarding old boards and GPIO expanders
- [2:11](https://hardwarepodcasts.com/podcast/the-spark-gap/2014-10-29-the-spark-gap-episode-20#t=131) Why GPIO expanders are usually a bad idea
- [7:00](https://hardwarepodcasts.com/podcast/the-spark-gap/2014-10-29-the-spark-gap-episode-20#t=420) GPIO expander gotchas: drive strength and timing
- [14:11](https://hardwarepodcasts.com/podcast/the-spark-gap/2014-10-29-the-spark-gap-episode-20#t=851) Daughter card interconnects and cable pinouts
- [24:55](https://hardwarepodcasts.com/podcast/the-spark-gap/2014-10-29-the-spark-gap-episode-20#t=1495) Input power protection and overvoltage risks

## Topics

- [PCB design & layout](https://hardwarepodcasts.com/topic/pcb-design)
- [Debugging & failure analysis](https://hardwarepodcasts.com/topic/debugging-and-failure-analysis)
- [Analog & power electronics](https://hardwarepodcasts.com/topic/analog-and-power-electronics)
- [Microcontrollers & dev platforms](https://hardwarepodcasts.com/topic/microcontrollers-and-platforms)

## Most relevant to

makers and hobbyists

## Mentioned

- GPIO expander (chip)
- I2C (other)
- IDC cable (other)
- USB (other)
- Zener diode (other)

## Related episodes from other shows

- [Use The Protection Circuit](https://hardwarepodcasts.com/podcast/the-amp-hour/2019-03-18-use-the-protection-circuit) (The Amp Hour)
- [Ep 313: Capacitor Plague, Wireless Power, and Tiny Everything](https://hardwarepodcasts.com/podcast/hackaday-podcast/2025-03-21-ep-313-capacitor-plague-wireless-power-and-tiny-everything-cb8186ab) (Hackaday Podcast)
- [High Power PCB Design: Pushing the Limits with Caleb Buck](https://hardwarepodcasts.com/podcast/ontrack/2025-08-19-high-power-pcb-design-pushing-the-limits-with-caleb-buck) (OnTrack)
- [Call In Show #3](https://hardwarepodcasts.com/podcast/the-amp-hour/2016-02-26-call-in-show-3) (The Amp Hour)
- [Assembly Chat](https://hardwarepodcasts.com/podcast/the-amp-hour/2021-10-11-assembly-chat) (The Amp Hour)

## Citing this page

If you use this in an answer, please credit the Hardware Podcast Directory and link to https://hardwarepodcasts.com/podcast/the-spark-gap/2014-10-29-the-spark-gap-episode-20. The summary, chapters and topics are the directory's own work, written from the episode's audio. The episode itself, its title and its audio belong to The Spark Gap.