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I have DS1307 small SMD parts so I can't simply leave out the resistors easily to make it work with 3.3V by default as with adafruit kit tutorial. How could I connect this device to my Raspberry Pi correctly? I assume I could add a resistor but I am not sure to what pins as this is I2C device.

Also what is the likelihood I damage either raspberry pi or rtc module by connecting it as is at 5V? Would it function properly?

Here's the front of the RTC:

DS1307 front

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  • since when PCB parts become "non-removable"? do you have a soldering iron?
    – lenik
    Jan 2, 2014 at 11:57
  • What I meat it's not a kit like adafruit RTC and it's not even easily removable because parts are so tiny. If you know what you are doing then of course they are easily removable. Question edited.
    – DominicM
    Jan 2, 2014 at 16:52

2 Answers 2

Reset to default
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R2 looks to be connected to the SDA pin. I guess R1 would be connected to SCL, and R3 to SQW. But you could just unsolder all three of them. You don't need those, as the Pi already has 1.8K resistors on the I2C lines.

SCL is just an input on the RTC and the SDA is an open drain, so all it does is pull the line to ground, so the RTC chip will never put 5V on any of those 2 pins. Minimal signal voltage required on the SCL and SDA lines is 2.2V so well below the 3.3V the Pi. So all should work fine once those resistors are removed.

(PS eBay has better RTC modules, for half the price)

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  • Thanks for the ebay tip, for a change ebay is better thought it's not quite half the price. Raspberry specific ones are actually quite expensive. Please see image in edit and let me know if your answer of removing all resistors is still true.
    – DominicM
    Jan 2, 2014 at 16:48
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    Definitely R1 and R2. You can clearly see the VCC trace on the left of them (coming in via the underside). I was talking about similar RTC modules going from $2,-. Though on those it's less easy to find the appropriate resistors to remove :-). You could however go with a slightly more expensive DS3231 module. Those will operate just fine on 3.3V, and they are also more accurate as an extra bonus. Starting at ±$4 (ebay.com/itm/…)
    – Gerben
    Jan 2, 2014 at 20:21
  • So if I remove R1 and R2 it will be safe to connect to the Pi? Also should I just remove or remove and solder a connection where resistor was? Problem with DS3231 is that it is difficult to set it up on the Pi at least in comparison to DS1307.
    – DominicM
    Jan 2, 2014 at 21:11
  • Only remove them! Going of the info on the adafruit page and in the datasheet, it is safe to connect it to the Pi.
    – Gerben
    Jan 3, 2014 at 14:27
  • Seems to have worked but now having issues with software end of it, not sure if it's hardware related or not. Any idea of the cause?: raspberrypi.stackexchange.com/questions/12724/…
    – DominicM
    Jan 4, 2014 at 17:04
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Connecting directly will damage the Pi.

It is possible to use a level translator (you will find many examples), but this seems overkill for this application.

What do you mean by "non removable parts". It is always possible to cut the resistor leads, or in extreme (e.g. for SMD) crush the resistor with a pair of pliers.

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  • Would it outright kill the Pi or damage some parts or it? Yes, I meant SMD but the issue is that it has 3 resistors and adafruit RTC has only 2 so it different design and I don't have enough experience to reverse engineer it.
    – DominicM
    Jan 2, 2014 at 3:08
  • This is the device I am talking about: dx.com/p/…
    – DominicM
    Jan 2, 2014 at 3:09
  • Connecting 5v to the Pi will most likely damage the GPIO pins, and possibly the whole SOC. I can't tell by looking at the image, but the link claims "Control interface level is 5V or 3.3V"
    – Milliways
    Jan 2, 2014 at 3:31
  • I noticed that too but I wouldn't trust the description at dx.com :) If I posted hi-res image of the front of the pcb would you be able to confirm?
    – DominicM
    Jan 2, 2014 at 12:31
  • I can't see how they could supply 3.3V with only 3 resistors on the PCB. Don't trust that.
    – Gerben
    Jan 2, 2014 at 15:51

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