RTC-SHIM (mini-HAT), a DS3231 battery driven real-time clock for Raspberry Pi.
"How did it come to this?" you may ask. The answer is simple. I was pissed off by the fact the several Pis I have all have the same issue. They lose time information when they switched off and need Internet to set proper time again. The obvious reason for this is lack of RTC chip and backup battery to count time when main CPU of Pi is off. This is how it's done in all modern PCs and notebooks (and Macs too). I've searched Internet and found no solution which suits my needs.
- The RTC board should be mounted on 40-pin connector of Raspberry Pi (like 2, 3, 4, zero have).
- The board should be mechanically and electrically compatible with all modern Pis (3+, 4, zero WH).
- The board should be mounted inside or outside the Pi's case.
- There should be possible to put some Pi HAT (Hardware Attached on Top) on top of the board (like LCD display, LoRa, LEDs array or 3G/4G modem HATs).
- The board should be obviously small enough to fit in case of Pi.
- The board should have a battery holder or/and a common notebook BIOS battery connector.
- The board should be easy to setup under Pi's Linux (like Raspbian or Ubuntu).
- The board should be cheap to buy or/and easy to manufacture by (my) hand at home.
And gradually I came with few designs presented here.
Raspberry Pi 40-pin RTC-SHIM mini-HAT.
Preview:
Features:
- DS3231 RTC chip
- double footprint for larger and smaller versions of the chip
- CR1220 3V battery
- locked Pi headers
- double set of Pi headers (for inside and outside mount)
- I2C0/I2C1 bus selection
- can be used as SHIM (no headers) or HAT (with headers)
- optional external notebook BIOS battery connector
CAM files are available.
Raspberry Pi RTC-mini-flip-SHIM micro-HAT.
Preview:
Features:
- DS3231 RTC chip
- double footprint for larger and smaller versions of the chip
- CR1220 3V battery
- locked Pi headers
- double mount on Pi headers (for inside and outside mount)
- very small size
- fits on 26- and 40-pin Pi headers
- optional external notebook BIOS battery connector (both side mount possible)
CAM files are available.
Raspberry Pi zero 40-pin RTC-zero-SHIM mini-HAT.
Preview:
Features:
- DS3231 RTC chip
- double footprint for larger and smaller versions of the chip
- CR2032/CR1220 3V battery
- locked Pi headers
- Pi zero board style
- I2C0/I2C1 bus selection
- can be used as SHIM (no headers) or HAT (with headers)
- optional external notebook BIOS battery connector
CAM files are available.
Bill Of Materials is currently available only for LCSC Electronic Components Distributor, which is probably cheapest anyway.
| Designator | Part/Value | Package/Footprint | LCSC # |
|---|---|---|---|
| BAT1 | CR1220-2 | SMD | C70381 |
| BAT2 | BS-8-1 | SMD | C70378 |
| C1** | Cap. 100nF | 0402 | C1525 |
| C2** | Cap. 1uF | 0603 | C15849 |
| IC1* | DS3231SN#T&R | SOIC-16_300mil | C9866 |
| IC2* | DS3231MZ+TRL | SOIC-8_150mil | C107410 |
| LIPO1, LIPO2 | A1251WV-2P | Through Hole,P=1.25mm | C225090 |
| R1, R2** | Res. 10K | 0402 | C25744 |
*) Only one of chips should be installed, either IC1 or IC2. **) These passive components are optional but it's recommended to install them.
- pinout.xyz - a brilliant resource on topic of Pi's pinout and HATs.
- raspberrypi/hats - Pi's HAT specification.
- RPI_RTC_Module_SKU:EP-0016 - some RTC schematics and setup info.
- Raspberry Pi RTC: Adding a Real Time Clock - RTC setup info.
Your contributions as code, resources, or finances are welcome! Please contact me directly via email at andriy.golovnya@gmail.com or through my GitHub profile.
If you'd like to make a financial contribution, you can donate via PayPal or Ko-Fi. Your support is greatly appreciated.
Thanks in advance!
