OnOff shim compatible with WaveShare 4in rPi LCD (A)?


#1

Hi there,

am just taking the first few steps along the path of pi tinkering and am working on a small project which is intended as a gift for a friend and i’d like to wire in a power button so they have control over when it is switched on as it’ll be enclosed in a case making plugging/unplugging difficult unless from the wall outlet.

currently I am using a small 4in lcd display from waveshare to output from the pi and this will be built into casing too.

doing some reading on the onoff shim i gather it uses pins 7 (bcm 4) and 11 (bcm 17) and there is potential for weird things to happen if other inputs/outputs are using those pins as well.

the specs for my display (from here: https://www.waveshare.com/product/4inch-rpi-lcd-a.htm) are as follows:

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

which looks like pin 11 (BCM 17) clashes with their touch panel interrupt, is that correct?

if so, the screen will be behind glass anyways so will not be touchable so do you guys think i may get away with it?

thanks in advance :)


#2

The Pi can be booted up by momentarily shorting the two RUN pins. I do this on my KODI Pi. I do the shutdown from the menu, but don’t unplug the power supply. When I want it to boot up again I just push a button (switch) I have wired up to the RUN pins. It’s a normally open momentary contact switch. Like a doorbell button.

The downside is you can’t use it to shut down. And you don’t want to press it while the Pi is running. It will force a reboot.

Just throwing out options.


#3

ooh thanks for that, that’s useful to know as well.