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I have a touchscreen that uses the following GPIO pins on my B+:

PIN NO.     SYMBOL  DESCRIPTION
1, 17   3.3V    Power positive (3.3V power input)
2, 4    5V  Power positive (5V power input)
3, 5, 7, 8, 10, 12, 13, 15, 16  NC  NC
6, 9, 14, 20, 25    GND     Ground
11  TP_IRQ  Touch Panel interrupt, low level while the Touch Panel detects touching
18  LCD_RS  Instruction/Data Register selection
19  LCD_SI / TP_SI  SPI data input of LCD/Touch Panel
21  TP_SO   SPI data output of Touch Panel
22  RST     Reset
23  LCD_SCK / TP_SCK    SPI clock of LCD/Touch Panel
24  LCD_CS  LCD chip selection, low active
26  TP_CS   Touch Panel chip selection, low active

See here for better formatting. My goal is to keep the screen and make the Make FM Pirate Radio Transmitter. However, it uses GPIO pin 4 for the transmitter, which is being used by the screen. So, my question is, are there any pins left that I can use for the transmitter because I know not all pins can do the same things. Or, can I use the same pin for two different tasks(I don't think you can but am not sure)? I would like to keep the same performance as would be had on pin four.

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1 Answer 1

Reset to default
2

Pin 4 is 5V supply, so you can use this for your transmitter as well as for your display - BUT note that this will draw additional current. You'd need to see if the rPi can supply sufficient current to both.

CORRECTION: The article says "Pin 4" but you can see clearly that they mean GPIO 4 (which is physically pin 7). As per your Display wiring, this pin is not used (I assume NC = No Connection). You could see if you could bend the antenna around the display and use it the way it was intended in the tool. I looked at the source and at the original PiFM wiki and it clearly says this FM transmitter trick works only with GPIO 4, so there is no way you could go into the source of the PiFM code and change the port to one of your free GPIO pins unfortunately.

ONE note of warning: This antenna can broadcast on already assigned frequencies, and even if you set it to an unused frequency it has harmonics that interfere with assigned frequencies. So be careful or else government agencies might come knocking ....

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  • If that is the case then how does this Transmitter work? It modulates the power supply pin?
    – NULL
    Commented May 22, 2015 at 1:12
  • Also, to avoid difficult hardware maneuvering I would like if possible to use a pin not shared by the screen.
    – NULL
    Commented May 22, 2015 at 1:13
  • 1
    I was wrong - I couldn't read the full PiFM article on my work computer as the Next button and links didn't work, but at home I had a chance to review it in its entirety. They do not mean the physical pin 4, but GPIO Pin 4 (physical pin 7). I have updated my answer.
    – Phil B.
    Commented May 22, 2015 at 1:33
  • You are certainly right!! Thanks for the info. I'll be carefull...hopefully:)
    – NULL
    Commented May 22, 2015 at 1:35

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