I've been reading about how to use the GPIO to toggle a button on a thing I've taken apart.
It's like this: Amazon
I watched a video of a guy using an opto-coupler, what are the basics here? I'm kind of new to circuitry.
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2Are you asking for advice on how to control the button, or on how to use an opto-coupler? Have you tried Google for the latter? What did you find and what did it leave unanswered? – Mark Smith Jun 22 '19 at 6:51
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Ah, this is neat. Suppose you have 3 Rpi's and you wish to select which Rpi to display on the one and only one HDMI monitor, using Rpi GPIO pin to "press" the button, instead of using the human hand to press the button. To do this you need to (1) open the box, (2) find the two contact points of the button, (3) check the nature of the switch, (4) if it is a mechanical switch, you can use a cheapy Rpi GPIO controlled 5V relay to do the switching. So you can now do both manual and Rpi software select. (5). /to continue, ... – tlfong01 Jun 22 '19 at 8:45
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(5) I have such a switch, with 5V power inputt. That means the button controls a 5V high low signal. This is a bit complicated. If the button is a "pull up" type, then you can use one GPIO pin, step up 3V3 logical signal to 5V, and connect to the button pull up resistor contact point, and that is it. WARNING: mess things at your own risk: I don't guarantee your HDMI mon will not explode! :) PS1 - If the button circuit is not pull up type, but sort of push/pull type, then sorry I can't help, because my broken English can't do. PS2- I am only guessing. I have NOT tried it myself! – tlfong01 Jun 22 '19 at 9:01
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Thank you all for your answers and edits! Much appreciated. Will read through when I get the time. – Quinn Finney Jun 22 '19 at 18:07
Question
How can Rpi GPIO toggle the HMDI selection button?
Short Answer
Yes, if your HDMI selector button is connected to a pull down resistor, and pressing the button pulls input signal at resistor to ground, releasing button pulls resistor to 5V.
What you need to do is to extract two wires from the button contacts, one is 5V logic input signal, the other wire is ground.
Since Rpi GPIO logic level is 3V3, so you need to use a level converter, such as the 2N2222 transistor pull up circuit, to pull Rpi GPIO 3V3 signal to 5V, then input to the HDMI button selector input. You can read more details of the wiring in the long answer below.
Long Answer
Suppose you have 3 Rpi's and you wish to select which Rpi to display on the one and only one HDMI monitor, using Rpi GPIO pin to "press" the button, instead of using the human hand to press the button. To do this you need to:
open the box,
find the two contact points of the button,
check the nature of the switch,
if it is a mechanical switch, you can use a cheap Rpi GPIO controlled 5V relay to do the switching. So you can now do both manual and Rpi software select.
I have such a switch, with 5V power input. That means the button controls a 5V high low signal. This is a bit complicated. If the button is a "pull up" type, then you can use one GPIO pin, step up 3V3 logical signal to 5V, and connect to the button pull up resistor contact point, and that is it.
WARNING: mess around things at your own risk: I don't guarantee your HDMI mon will not explode! :)
Update 2019jun22hkt2023
My cheapy US$7 HDMI splitter actually IR remote control
HDMI Switch 3 Port Video Splitter 3 In 1 Out IR Remote Control - US$7
So I think it is much safer and easier to DIY a Rpi GPIO IR remote controller, than to mess around with the electronic button circuit.
References
Raspberry Pi Zero Universal Remote Instructable – bbtinkerer, instructables 2018
AliExpress Universal TV Remote Control US$2.34
TSAL6200e IR LED Datasheet – Vishay
TSOP38238 IR Receiver – Vishay
HobbyElectronics HX1838 Infrared Remote Control Module and Receiver - £5.4
TaoBao HX1838 Infrared Remote Control Module and Receiver - ¥2
Appendices
Appendix A - Rpi GPIO controlled IR Universal Remote
Appendix B - HDMI selector button connection
Update 2019jul08hkt2114
Appendix C - IR Modules
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Thank you for the detailed answer I will ask some questions when I get the time!! – Quinn Finney Jun 22 '19 at 18:08
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Do you wire the GPIO to the IR remote controller, or would you use an IR reader to read what it is sending and replicate it? That solution sounds much better and would also allow actual control of 1 2 or 3 instead of toggling between. – Quinn Finney Jun 22 '19 at 21:04
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@Quinn Finney, I have added a reference section with universal remote.stuff. You might like to skim through them to get a rough idea of how things work. The first reference uses RpiZero to DIY a remote is OK for newbies. – tlfong01 Jun 23 '19 at 1:28
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1) substitute a relay for the button press - that way you don't need to worry about voltages, common grounds, pull ups, or pull downs. Eg https://www.instructables.com/id/Control-Any-Remote-From-a-Raspberry-Pi-and-Amazon-/ 2) Or find an HDMI switcher with a computer input, for example the ATEN HDMI switcher has an RS232 input.
The button on the HDMI switcher you're using is a toggle which cycles round the inputs. unless you also read back the LED to know which one is selected, you're likely to miss a keypress, get out of synch, and not know which input you have switched to.
