Uploaded December 2023 | Updated September 2026, 1 week ago
In this video I use the GPIO lines to “bit bang” the Serial Peripheral Interface (SPI) protocol. I’m open to a discussion on keeping SPI as pure code, creating a full implementation of the protocol in hardware or trying a hybrid approach aiming to get maximal improvement from minimal components. My test device is a DS1391U, these only come as SMD parts but I soldered one onto a dip adapter about a year ago which should give you some idea of how far off my time estimates on this project are. This is a programming heavy video, feel free to use the chapter times to skip it if you just want to see results. Part of the footage are slightly out of focus due to a mistake I made in camera setup, something else to be careful of in future. Fortunately it matters less here that in many of the build videos with more complicated circuits. Special thanks to my friend Ben who ran the affected footage through a deblur program and made it a bit better.
The Dip Adapter for the DS1391U chip: youtu.be/pntOYA8YL8w
0:00 Introduction
0:41 SPI Introduction
2:51 DS1391U RTC Datasheet
4:57 Wiring the device in
9:47 First Test
11:42 Read (Coding)
15:09 Read (Test)
18:07 Write (Coding)
20:38 Write (Test)
21:37 Backup Battery
22:34 Setting time and date the hard way
25:08 Counting Cycles
27:09 Outro
28:53 The Next Day
In this video I use the GPIO lines to “bit bang” the Serial Peripheral Interface (SPI) protocol. I’m open to a discussion on keeping SPI as pure code, creating a full implementation of the protocol in hardware or trying a hybrid approach aiming to get maximal improvement from minimal components. My test device is a DS1391U, these only come as SMD parts but I soldered one onto a dip adapter about a year ago which should give you some idea of how far off my time estimates on this project are. This is a programming heavy video, feel free to use the chapter times to skip it if you just want to see results. Part of the footage are slightly out of focus due to a mistake I made in camera setup, something else to be careful of in future. Fortunately it matters less here that in many of the build videos with more complicated circuits. Special thanks to my friend Ben who ran the affected footage through a deblur program and made it a bit better.
The Dip Adapter for the DS1391U chip: youtu.be/pntOYA8YL8w
0:00 Introduction
0:41 SPI Introduction
2:51 DS1391U RTC Datasheet
4:57 Wiring the device in
9:47 First Test
11:42 Read (Coding)
15:09 Read (Test)
18:07 Write (Coding)
20:38 Write (Test)
21:37 Backup Battery
22:34 Setting time and date the hard way
25:08 Counting Cycles
27:09 Outro
28:53 The Next Day
