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Hard wire RTC?

toddh86

I'm looking for advice on best way to proceed with a small pi project I'm making.

 

Overview

I'm making a countdown timer to my wifes due date for our first child. To achieve this I'm using an old RaspPi Model B and a WaveShare SpotPear 4Inch RPiLCD (A) and a 3D printed case with a python script to perform the  countdown.

I have it all working OK except for that I need to make it stand alone as she works in an office where she will not be able to connect it to a network (wired or wireless) so I purchased a RTC to add into the Pi to give it a proper clock.

 

Issue comes when constructing the 3 components. The screen and the RTC both use the GPIO pins, with the screen taking all of the pins (I doubt all pins are required by the screen but the connector takes up all pins) and the RTC taking up 10 (2x5) whichi I doubt it uses all.

 

My question is, can I reloate the RTC elsewhere to other parts of the board? Is there a better product for doing this? I have uploaded pictures of all the components as well, all help is welcome and appreciated!

 

Cheeers,

 

Todd

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  • 0

    Hi Todd,

     

    Most of these small TFT screens for the Pi use 'SPI' (Serial Peripheral Interface), which is a serial interface that only uses a handful of pins. The RTC most likely uses a different interface called I2C (Inter-Integrated Circuit), and the Pi has different pins allocated for SPI and I2C, so there isn't usually any clash at all (the LCD screen _may_ also use I2C, but there is no clash with adding additional devices to the I2C bus, it is designed for that, so again no issue).

     

    So, long story short, electrically there should be no issue with connecting them both up. However, physically you have the problem that they won't fit, since the screen plugs on top of all the pins. Your only simple solution is to see what pins are used on the RTC board, and manually patch wires (using a soldering iron) between the RTC board and the LCD board, such that when the LCD board is plugged onto the Pi, then the correct RTC connections are made too. There are not really other simple alternatives here unfortunately, Still, it is an easy thing to do (requires soldering iron and thin solder and wire of course). Unfortunately I'm not aware of a TFT board with built-in RTC.

     

    Finally, there _may_ be one or two other input/output pins used by the RTC, so you'd need to verify that they do not clash. It is likely the RTC will run without them connected, if you find there is a clash.

    You can refer to the diagram below for a list of the pin assignments. The I2C pins are labelled SDA and SCL (data and clock pins respectively).

     

    I hope that helps!

     

    image

Reply
  • 0

    Hi Todd,

     

    Most of these small TFT screens for the Pi use 'SPI' (Serial Peripheral Interface), which is a serial interface that only uses a handful of pins. The RTC most likely uses a different interface called I2C (Inter-Integrated Circuit), and the Pi has different pins allocated for SPI and I2C, so there isn't usually any clash at all (the LCD screen _may_ also use I2C, but there is no clash with adding additional devices to the I2C bus, it is designed for that, so again no issue).

     

    So, long story short, electrically there should be no issue with connecting them both up. However, physically you have the problem that they won't fit, since the screen plugs on top of all the pins. Your only simple solution is to see what pins are used on the RTC board, and manually patch wires (using a soldering iron) between the RTC board and the LCD board, such that when the LCD board is plugged onto the Pi, then the correct RTC connections are made too. There are not really other simple alternatives here unfortunately, Still, it is an easy thing to do (requires soldering iron and thin solder and wire of course). Unfortunately I'm not aware of a TFT board with built-in RTC.

     

    Finally, there _may_ be one or two other input/output pins used by the RTC, so you'd need to verify that they do not clash. It is likely the RTC will run without them connected, if you find there is a clash.

    You can refer to the diagram below for a list of the pin assignments. The I2C pins are labelled SDA and SCL (data and clock pins respectively).

     

    I hope that helps!

     

    image

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