Shop OBEX P1 Docs P2 Docs Learn Events
DS1307 connections to the propeller — Parallax Forums

DS1307 connections to the propeller

El PaisaEl Paisa Posts: 375
edited 2007-03-17 17:08 in Propeller 1
I have a Sparkfun RTC module that would like to connect to the demoboard.
Shall I connect the module to the +5V and use resistors in series with SDA and SCL or connect the module to the +3.3V?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-03-17 16:32
    The DS1307 requires a 5V supply, so you can't run it at 3.3V. The SCL signal is an input to the DS1307 and the SDA is an open-drain pin, so strictly speaking, you shouldn't need a series resistor on either. I would still use a 100 ohm series resistor strictly for protection against faults (accidentally connecting to +5V). This would limit any fault current to 20ma (5V-3V = 2V through 100 ohms = 20ma). Your pullup for SDA should be to +3.3V
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-03-17 17:08
    As a note, the DS1302 will run at 3.3V…With a 3V lithium coil cell battery for the backup it still functions normally without power as well. That’s my preferred RTC and easy to implement with a lot of example code and documentation available.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
Sign In or Register to comment.